/*!
 * Copyright (c) 2026-present, Vanilagy and contributors
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/.
 */

import { buildAacAudioSpecificConfig, parseAacAudioSpecificConfig } from '../shared/aac-misc';
import {
	AUDIO_CODECS,
	AudioCodec,
	MediaCodec,
	parsePcmCodec,
	PCM_AUDIO_CODECS,
	PcmAudioCodec,
	SUBTITLE_CODECS,
	SubtitleCodec,
	VIDEO_CODECS,
	VideoCodec,
} from './codec';
import { OutputAudioTrack, OutputSubtitleTrack, OutputTrack, OutputVideoTrack } from './output';
import {
	assert,
	assertNever,
	binarySearchLessOrEqual,
	CallSerializer,
	clamp,
	clearIntervalUnthrottled,
	floorToDivisor,
	last,
	promiseWithResolvers,
	roundToDivisor,
	setInt24,
	setIntervalUnthrottled,
	setUint24,
	toUint8Array,
	UnthrottledTimerHandle,
} from './misc';
import { Muxer } from './muxer';
import { SubtitleParser } from './subtitles';
import { toAlaw, toUlaw } from './pcm';
import {
	CustomVideoEncoder,
	CustomAudioEncoder,
	customVideoEncoders,
	customAudioEncoders,
} from './custom-coder';
import { EncodedPacket, EncodedPacketSideData, PacketType } from './packet';
import {
	AudioSample,
	audioSampleToInterleavedFormat,
	toInterleavedAudioFormat,
	VideoSample,
	VideoSamplePixelFormat,
} from './sample';
import {
	AudioEncodingConfig,
	buildAudioEncoderConfig,
	buildVideoEncoderConfig,
	validateAudioEncodingConfig,
	validateVideoEncodingConfig,
	VideoEncodingConfig,
} from './encode';
import { AudioResampler } from './resample';
import { determineVideoPacketType } from './codec-data';

/**
 * Base class for media sources. Media sources are used to add media samples to an output file.
 * @group Media sources
 * @public
 */
export abstract class MediaSource {
	/** @internal */
	abstract readonly _codec: MediaCodec;
	/** @internal */
	_connectedTrack: OutputTrack | null = null;
	/** @internal */
	_closingPromise: Promise<void> | null = null;
	/** @internal */
	_closed = false;

	/** @internal */
	_ensureValidAdd() {
		if (!this._connectedTrack) {
			throw new Error('Source is not connected to an output track.');
		}

		if (this._connectedTrack.output.state === 'canceled') {
			throw new Error('Output has been canceled.');
		}

		if (this._connectedTrack.output.state === 'finalizing' || this._connectedTrack.output.state === 'finalized') {
			throw new Error('Output has been finalized.');
		}

		if (this._connectedTrack.output.state === 'pending') {
			throw new Error('Output has not started.');
		}

		if (this._closed) {
			throw new Error('Source is closed.');
		}
	}

	/** @internal */
	async _start() {}
	/** @internal */
	// eslint-disable-next-line @typescript-eslint/no-unused-vars
	async _flushAndClose(forceClose: boolean) {}

	/**
	 * Closes this source. This prevents future samples from being added and signals to the output file that no further
	 * samples will come in for this track. Calling `.close()` is optional but recommended after adding the
	 * last sample - for improved performance and reduced memory usage.
	 */
	close() {
		if (this._closingPromise) {
			return;
		}

		const connectedTrack = this._connectedTrack;

		if (!connectedTrack) {
			throw new Error('Cannot call close without connecting the source to an output track.');
		}

		if (connectedTrack.output.state === 'pending') {
			throw new Error('Cannot call close before output has been started.');
		}

		this._closingPromise = (async () => {
			await this._flushAndClose(false);

			this._closed = true;

			if (connectedTrack.output.state === 'finalizing' || connectedTrack.output.state === 'finalized') {
				return;
			}

			connectedTrack.output._muxer.onTrackClose(connectedTrack);
		})();
	}

	/** @internal */
	async _flushOrWaitForOngoingClose(forceClose: boolean) {
		return this._closingPromise ??= (async () => {
			await this._flushAndClose(forceClose);
			this._closed = true;
		})();
	}
}

/**
 * Base class for video sources - sources for video tracks.
 * @group Media sources
 * @public
 */
export abstract class VideoSource extends MediaSource {
	/** @internal */
	override _connectedTrack: OutputVideoTrack | null = null;
	/** @internal */
	override readonly _codec: VideoCodec;

	/** Internal constructor. */
	constructor(codec: VideoCodec) {
		super();

		if (!VIDEO_CODECS.includes(codec)) {
			throw new TypeError(`Invalid video codec '${codec}'. Must be one of: ${VIDEO_CODECS.join(', ')}.`);
		}

		this._codec = codec;
	}
}

const maybeEnsureIsKeyPacket = (track: OutputVideoTrack, packet: EncodedPacket) => {
	if (track.metadata.hasOnlyKeyPackets && packet.type !== 'key') {
		throw new Error('Cannot add non-key packets to a hasOnlyKeyPackets video track.');
	}
};

/**
 * The most basic video source; can be used to directly pipe encoded packets into the output file.
 * @group Media sources
 * @public
 */
export class EncodedVideoPacketSource extends VideoSource {
	/** Creates a new {@link EncodedVideoPacketSource} whose packets are encoded using `codec`. */
	constructor(codec: VideoCodec) {
		super(codec);
	}

	/**
	 * Adds an encoded packet to the output video track. Packets must be added in *decode order*, while a packet's
	 * timestamp must be its *presentation timestamp*. B-frames are handled automatically.
	 *
	 * @param meta - Additional metadata from the encoder. You should pass this for the first call, including a valid
	 * decoder config.
	 *
	 * @returns A Promise that resolves once the output is ready to receive more samples. You should await this Promise
	 * to respect writer and encoder backpressure.
	 */
	add(packet: EncodedPacket, meta?: EncodedVideoChunkMetadata) {
		if (!(packet instanceof EncodedPacket)) {
			throw new TypeError('packet must be an EncodedPacket.');
		}
		if (packet.isMetadataOnly) {
			throw new TypeError('Metadata-only packets cannot be added.');
		}
		if (meta !== undefined && (!meta || typeof meta !== 'object')) {
			throw new TypeError('meta, when provided, must be an object.');
		}

		this._ensureValidAdd();

		maybeEnsureIsKeyPacket(this._connectedTrack!, packet);
		return this._connectedTrack!.output._muxer.addEncodedVideoPacket(this._connectedTrack!, packet, meta);
	}
}

class VideoEncoderWrapper {
	private ensureEncoderPromise: Promise<void> | null = null;
	private encoderInitialized = false;
	private encoder: VideoEncoder | null = null;
	private muxer: Muxer | null = null;
	private lastMultipleOfKeyFrameInterval = -1;
	private emittedEncoderPackets = 0;

	// Tracks the input dimensions of the first frame
	private codedWidth: number | null = null;
	private codedHeight: number | null = null;
	// Tracks the output dimensions of the first frame (used to lock dimensions for fill/contain/cover)
	private outputWidth: number | null = null;
	private outputHeight: number | null = null;

	// Frame rate normalization state
	private frameRateLastSample: VideoSample | null = null;
	private frameRateLastTimestamp: number | null = null;
	private frameRateLastEndTimestamp: number | null = null;

	// VideoEncoder converts everything to microseconds, so we need to do some bookkeeping to restore the original
	// timing information
	private preciseTimings: {
		microsecondTimestamp: number;
		timestamp: number;
		duration: number;
		timestampIsValid: boolean;
		durationIsValid: boolean;
	}[] = [];

	private customEncoder: CustomVideoEncoder | null = null;
	private customEncoderCallSerializer = new CallSerializer();
	private customEncoderQueueSize = 0;

	// Alpha stuff
	private alphaEncoder: VideoEncoder | null = null;
	private splitter: ColorAlphaSplitter | null = null;
	private splitterCreationFailed = false;
	private alphaFrameQueue: (VideoFrame | null)[] = [];

	/**
	 * Encoders typically throw their errors "out of band", meaning asynchronously in some other execution context.
	 * However, we want to surface these errors to the user within the normal control flow, so they don't go uncaught.
	 * So, we keep track of the encoder error and throw it as soon as we get the chance.
	 */
	private error: Error | null = null;

	private lastMuxerPromise: Promise<void> = Promise.resolve();

	constructor(private source: VideoSource, private encodingConfig: VideoEncodingConfig) {}

	async add(videoSample: VideoSample, shouldClose: boolean, encodeOptions?: VideoEncoderEncodeOptions) {
		const originalSample = videoSample;

		try {
			this.checkForEncoderError();
			this.source._ensureValidAdd();

			const config = this.encodingConfig;
			const sizeChangeBehavior = config.sizeChangeBehavior ?? 'deny';
			let isSizeChange = false;

			// Ensure video sample size remains constant or handle the change
			if (this.codedWidth !== null && this.codedHeight !== null) {
				if (videoSample.codedWidth !== this.codedWidth || videoSample.codedHeight !== this.codedHeight) {
					isSizeChange = true;
					if (sizeChangeBehavior === 'deny') {
						throw new Error(
							`Video sample size must remain constant. Expected ${this.codedWidth}x${this.codedHeight},`
							+ ` got ${videoSample.codedWidth}x${videoSample.codedHeight}. To allow the sample size to`
							+ ` change over time, set \`sizeChangeBehavior\` to a value other than 'deny' in the`
							+ ` encoding options.`,
						);
					}
				}
			} else {
				this.codedWidth = videoSample.codedWidth;
				this.codedHeight = videoSample.codedHeight;
			}

			// Determine if we need to apply transformations via canvas
			const hasTransformConfig = config.transform?.width !== undefined
				|| config.transform?.height !== undefined
				|| config.transform?.rotate !== undefined
				|| config.transform?.crop !== undefined
				|| config.transform?.force === true;
			const needsTransform = hasTransformConfig || (isSizeChange && sizeChangeBehavior !== 'passThrough');

			if (needsTransform) {
				let targetWidth = config.transform?.width;
				let targetHeight = config.transform?.height;
				let appliedFit: 'fill' | 'contain' | 'cover' = config.transform?.fit ?? 'fill';

				// If the size changed and behavior is fill/contain/cover, lock to the original output dimensions
				if (isSizeChange && sizeChangeBehavior !== 'passThrough') {
					assert(this.outputWidth);
					assert(this.outputHeight);
					assert(sizeChangeBehavior !== 'deny');

					targetWidth = this.outputWidth!;
					targetHeight = this.outputHeight!;
					appliedFit = sizeChangeBehavior;
				}

				const transformed = await videoSample.transform({
					width: targetWidth,
					height: targetHeight,
					roundDimensionsTo: 2,
					crop: config.transform?.crop,
					rotate: config.transform?.rotate,
					fit: appliedFit,
					alpha: config.alpha,
				});

				// Save the output dimensions of the first frame
				if (this.outputWidth === null || this.outputHeight === null) {
					this.outputWidth = transformed.displayWidth;
					this.outputHeight = transformed.displayHeight;
				}

				if (shouldClose) {
					videoSample.close();
				}

				videoSample = transformed;
				shouldClose = true;
			} else {
				// If no canvas is needed, we still need to record the output dimensions for the first frame
				if (this.outputWidth === null || this.outputHeight === null) {
					this.outputWidth = videoSample.codedWidth;
					this.outputHeight = videoSample.codedHeight;
				}
			}

			const frameRate = config.transform?.frameRate;
			if (frameRate !== undefined) {
				// Apply frame rate normalization
				const originalEndTimestamp = videoSample.timestamp + videoSample.duration;
				const alignedTimestamp = floorToDivisor(videoSample.timestamp, frameRate);

				if (this.frameRateLastSample !== null) {
					if (alignedTimestamp <= this.frameRateLastTimestamp!) {
						// Same frame rate slot, replace stored sample with the newer one
						this.frameRateLastSample.close();
						this.frameRateLastSample = videoSample.clone();
						this.frameRateLastEndTimestamp = originalEndTimestamp;
						return;
					} else {
						// Pad the gap by repeating the previous frame
						await this.padFrameRate(alignedTimestamp, encodeOptions);
					}
				}

				// Clone if the sample is still the user's, to avoid mutating externally-owned data
				if (videoSample === originalSample) {
					videoSample = videoSample.clone();
					shouldClose = true;
				}

				videoSample.setTimestamp(alignedTimestamp);
				videoSample.setDuration(1 / frameRate);

				this.frameRateLastSample?.close();
				this.frameRateLastSample = videoSample.clone();
				this.frameRateLastTimestamp = alignedTimestamp;
				this.frameRateLastEndTimestamp = originalEndTimestamp;
			}

			await this.processAndEncode(videoSample, encodeOptions);
		} finally {
			if (shouldClose) {
				videoSample.close();
			}
		}
	}

	/**
	 * Runs the process function (if any) and encodes the resulting samples.
	 */
	private async processAndEncode(
		videoSample: VideoSample,
		encodeOptions?: VideoEncoderEncodeOptions,
	) {
		const config = this.encodingConfig;
		let samplesToEncode: VideoSample[];

		// Apply the user-defined process function, if any
		if (config.transform?.process) {
			let processed = config.transform.process(videoSample);
			if (processed instanceof Promise) {
				processed = await processed;
			}

			if (processed === null) {
				return;
			}

			if (!Array.isArray(processed)) {
				processed = [processed];
			}

			samplesToEncode = processed.map((x) => {
				if (x instanceof VideoSample) {
					return x;
				}

				if (typeof VideoFrame !== 'undefined' && x instanceof VideoFrame) {
					return new VideoSample(x);
				}

				return new VideoSample(x as CanvasImageSource, {
					timestamp: videoSample.timestamp,
					duration: videoSample.duration,
				});
			});
		} else {
			samplesToEncode = [videoSample];
		}

		try {
			for (const sampleToEncode of samplesToEncode) {
				if (!this.encoderInitialized) {
					if (!this.ensureEncoderPromise) {
						this.ensureEncoder(sampleToEncode);
					}

					// No, this "if" statement is not useless. Sometimes, the above call to
					// `ensureEncoder` might have synchronously completed and the encoder is
					// already initialized. In this case, we don't need to await the promise
					// anymore. This also fixes nasty async race condition bugs when multiple
					// code paths are calling this method: It's important that the call that
					// initialized the encoder go through this code first.
					if (!this.encoderInitialized) {
						await this.ensureEncoderPromise;
					}
				}
				assert(this.encoderInitialized);

				const keyFrameInterval = this.encodingConfig.keyFrameInterval ?? 2;
				const multipleOfKeyFrameInterval = Math.floor(sampleToEncode.timestamp / keyFrameInterval);

				// Ensure a key frame every keyFrameInterval seconds. It is important that all video tracks
				// follow the same "key frame" rhythm, because aligned key frames are required to start new
				// fragments in ISOBMFF or clusters in Matroska (or at least desirable).
				const finalEncodeOptions = {
					...encodeOptions,
					keyFrame: encodeOptions?.keyFrame
						|| keyFrameInterval === 0
						|| multipleOfKeyFrameInterval !== this.lastMultipleOfKeyFrameInterval,
				};
				this.lastMultipleOfKeyFrameInterval = multipleOfKeyFrameInterval;

				if (this.customEncoder) {
					this.customEncoderQueueSize++;

					// We clone the sample so it cannot be closed on us from the outside before it reaches the encoder
					const clonedSample = sampleToEncode.clone();

					const promise = this.customEncoderCallSerializer
						.call(() => this.customEncoder!.encode(clonedSample, finalEncodeOptions))
						.then(() => this.customEncoderQueueSize--)
						.catch((error: Error) => this.error ??= error)
						.finally(() => {
							clonedSample.close();
						});

					if (this.customEncoderQueueSize >= 4) {
						await promise;
					}
				} else {
					assert(this.encoder);

					const videoFrame = sampleToEncode.toVideoFrame();

					const preciseTimingIndex = binarySearchLessOrEqual(
						this.preciseTimings,
						videoFrame.timestamp,
						x => x.microsecondTimestamp,
					);
					const existingEntry = preciseTimingIndex !== -1
						? this.preciseTimings[preciseTimingIndex]
						: null;
					if (existingEntry && existingEntry.microsecondTimestamp === videoFrame.timestamp) {
						if (existingEntry.timestamp !== sampleToEncode.timestamp) {
							// Mapping isn't unique, can't use the timestamp
							existingEntry.timestampIsValid = false;
						}
						if (existingEntry.duration !== sampleToEncode.duration) {
							// Mapping isn't unique, can't use the duration
							existingEntry.durationIsValid = false;
						}
					} else {
						this.preciseTimings.splice(preciseTimingIndex + 1, 0, {
							microsecondTimestamp: videoFrame.timestamp,
							timestamp: sampleToEncode.timestamp,
							duration: sampleToEncode.duration,
							timestampIsValid: true,
							durationIsValid: true,
						});

						// Make sure it doesn't grow indefinitely
						if (this.preciseTimings.length > 128) {
							this.preciseTimings.shift();
						}
					}

					if (!this.alphaEncoder) {
						// No alpha encoder, simple case
						this.encoder.encode(videoFrame, finalEncodeOptions);
						videoFrame.close();
					} else {
						// We're expected to encode alpha as well
						const frameDefinitelyHasNoAlpha = !!videoFrame.format && !videoFrame.format.includes('A');

						if (frameDefinitelyHasNoAlpha || this.splitterCreationFailed) {
							this.alphaFrameQueue.push(null);
							this.encoder.encode(videoFrame, finalEncodeOptions);
							videoFrame.close();
						} else {
							const width = videoFrame.displayWidth;
							const height = videoFrame.displayHeight;

							if (!this.splitter) {
								this.splitter = new ColorAlphaSplitter(width, height);
							}

							// The splitter takes ownership, so no need to close the frames ourselves
							const { colorFrame, alphaFrame } = await this.splitter.update(videoFrame);

							this.alphaFrameQueue.push(alphaFrame);
							this.encoder.encode(colorFrame, finalEncodeOptions);
							colorFrame.close();
						}
					}

					// We need to do this after sending the frame to the encoder as the frame otherwise might be closed
					if (this.encoder.encodeQueueSize >= 4) {
						await new Promise(resolve =>
							this.encoder!.addEventListener('dequeue', resolve, { once: true }),
						);
					}
				}

				await this.lastMuxerPromise; // Allow the writer to apply backpressure
			}
		} finally {
			for (const sample of samplesToEncode) {
				if (sample !== videoSample) {
					sample.close();
				}
			}
		}
	}

	/** Repeats the last frame rate sample to fill the gap up to the given timestamp. */
	private async padFrameRate(until: number, encodeOptions?: VideoEncoderEncodeOptions) {
		const frameRate = this.encodingConfig.transform!.frameRate!;
		assert(this.frameRateLastSample);

		const frameDifference = Math.round((until - this.frameRateLastTimestamp!) * frameRate);

		for (let i = 1; i < frameDifference; i++) {
			const sample = this.frameRateLastSample.clone();
			sample.setTimestamp(this.frameRateLastTimestamp! + i / frameRate);
			sample.setDuration(1 / frameRate);
			await this.processAndEncode(sample, encodeOptions);
			sample.close();
		}
	}

	private ensureEncoder(videoSample: VideoSample) {
		this.ensureEncoderPromise = (async () => {
			const encoderConfig = buildVideoEncoderConfig({
				...this.encodingConfig,
				width: videoSample.codedWidth,
				height: videoSample.codedHeight,
				squarePixelWidth: videoSample.squarePixelWidth,
				squarePixelHeight: videoSample.squarePixelHeight,
				framerate: this.source._connectedTrack?.metadata.frameRate,
			});
			this.encodingConfig.onEncoderConfig?.(encoderConfig);

			const MatchingCustomEncoder = customVideoEncoders.find(x => x.supports(
				this.encodingConfig.codec,
				encoderConfig,
			));

			if (MatchingCustomEncoder) {
				// @ts-expect-error "Can't create instance of abstract class 🤓"
				this.customEncoder = new MatchingCustomEncoder() as CustomVideoEncoder;
				// @ts-expect-error It's technically readonly
				this.customEncoder.codec = this.encodingConfig.codec;
				// @ts-expect-error It's technically readonly
				this.customEncoder.config = encoderConfig;
				// @ts-expect-error It's technically readonly
				this.customEncoder.onPacket = (packet, meta) => {
					if (!(packet instanceof EncodedPacket)) {
						throw new TypeError('The first argument passed to onPacket must be an EncodedPacket.');
					}
					if (meta !== undefined && (!meta || typeof meta !== 'object')) {
						throw new TypeError('The second argument passed to onPacket must be an object or undefined.');
					}

					maybeEnsureIsKeyPacket(this.source._connectedTrack!, packet);

					this.encodingConfig.onEncodedPacket?.(packet, meta);
					this.lastMuxerPromise
						= this.muxer!.addEncodedVideoPacket(this.source._connectedTrack!, packet, meta)
							.catch((error) => {
								this.error ??= error;
							});
				};

				await this.customEncoder.init();
			} else {
				if (typeof VideoEncoder === 'undefined') {
					throw new Error('VideoEncoder is not supported by this browser.');
				}

				encoderConfig.alpha = 'discard'; // Since we handle alpha ourselves

				if (this.encodingConfig.alpha === 'keep') {
					// Encoding alpha requires using two parallel encoders, so we need to make sure they stay in sync
					// and that neither of them drops frames. Setting latencyMode to 'quality' achieves this, because
					// "User Agents MUST not drop frames to achieve the target bitrate and/or framerate."
					encoderConfig.latencyMode = 'quality';
				}

				const hasOddDimension = encoderConfig.width % 2 === 1 || encoderConfig.height % 2 === 1;
				if (
					hasOddDimension
					&& (this.encodingConfig.codec === 'avc' || this.encodingConfig.codec === 'hevc')
				) {
					// Throw a special error for this case as it gets hit often
					throw new Error(
						`The dimensions ${encoderConfig.width}x${encoderConfig.height} are not supported for codec`
						+ ` '${this.encodingConfig.codec}'; both width and height must be even numbers. Make sure to`
						+ ` round your dimensions to the nearest even number.`,
					);
				}

				const support = await VideoEncoder.isConfigSupported(encoderConfig);
				if (!support.supported) {
					throw new Error(
						`This specific encoder configuration (${encoderConfig.codec}, ${encoderConfig.bitrate} bps,`
						+ ` ${encoderConfig.width}x${encoderConfig.height}, hardware acceleration:`
						+ ` ${encoderConfig.hardwareAcceleration ?? 'no-preference'}) is not supported by this browser.`
						+ ` Consider using another codec or changing your video parameters.`,
					);
				}

				/** Queue of color chunks waiting for their alpha counterpart. */
				const colorChunkQueue: {
					chunk: EncodedVideoChunk;
					meta: EncodedVideoChunkMetadata | undefined;
				}[] = [];
				/** Each value is the number of encoded alpha chunks at which a null alpha chunk should be added. */
				const nullAlphaChunkQueue: number[] = [];
				let encodedAlphaChunkCount = 0;
				let alphaEncoderQueue = 0;

				const addPacket = (
					colorChunk: EncodedVideoChunk,
					alphaChunk: EncodedVideoChunk | null,
					meta: EncodedVideoChunkMetadata | undefined,
				) => {
					const sideData: EncodedPacketSideData = {};

					if (alphaChunk) {
						const alphaData = new Uint8Array(alphaChunk.byteLength);
						alphaChunk.copyTo(alphaData);

						sideData.alpha = alphaData;
					}

					let packet = EncodedPacket.fromEncodedChunk(colorChunk, sideData);

					// See if there's a relevant timing entry to refine the packet's timing data
					const preciseTimingIndex = binarySearchLessOrEqual(
						this.preciseTimings,
						colorChunk.timestamp,
						x => x.microsecondTimestamp,
					);
					const entry = preciseTimingIndex !== -1
						? this.preciseTimings[preciseTimingIndex]
						: null;

					let actualType: PacketType | null = null;
					if (this.emittedEncoderPackets === 0 && packet.type === 'delta' && meta?.decoderConfig) {
						// https://github.com/Vanilagy/mediabunny/issues/365
						// We expect the first packet to be a key packet. If it's not, let's actually verify that it's
						// not by getting the actual type.
						actualType = determineVideoPacketType(
							this.encodingConfig.codec,
							meta.decoderConfig,
							packet.data,
						);
					}

					// Define the packet
					if ((entry && entry.microsecondTimestamp === colorChunk.timestamp) || actualType !== null) {
						packet = packet.clone({
							timestamp: entry?.timestampIsValid ? entry.timestamp : undefined,
							duration: entry?.durationIsValid ? entry.duration : undefined,
							type: actualType ?? undefined,
						});
					}

					maybeEnsureIsKeyPacket(this.source._connectedTrack!, packet);

					this.encodingConfig.onEncodedPacket?.(packet, meta);
					this.lastMuxerPromise
						= this.muxer!.addEncodedVideoPacket(this.source._connectedTrack!, packet, meta)
							.catch((error) => {
								this.error ??= error;
							});

					this.emittedEncoderPackets++;
				};

				const stack = new Error('Encoding error').stack;

				this.encoder = new VideoEncoder({
					output: (chunk, meta) => {
						if (!this.alphaEncoder) {
							// We're done
							addPacket(chunk, null, meta);
							return;
						}

						const alphaFrame = this.alphaFrameQueue.shift();
						assert(alphaFrame !== undefined);

						if (alphaFrame) {
							this.alphaEncoder.encode(alphaFrame, {
								// Crucial: The alpha frame is forced to be a key frame whenever the color frame
								// also is. Without this, playback can glitch and even crash in some browsers.
								// This is the reason why the two encoders are wired in series and not in parallel.
								keyFrame: chunk.type === 'key',
							});
							alphaEncoderQueue++;
							alphaFrame.close();
							colorChunkQueue.push({ chunk, meta });
						} else {
							// There was no alpha component for this frame
							if (alphaEncoderQueue === 0) {
								// No pending alpha encodes either, so we're done
								addPacket(chunk, null, meta);
							} else {
								// There are still alpha encodes pending, so we can't add the packet immediately since
								// we'd end up with out-of-order packets. Instead, let's queue a null alpha chunk to be
								// added in the future, after the current encoder workload has completed:
								nullAlphaChunkQueue.push(encodedAlphaChunkCount + alphaEncoderQueue);
								colorChunkQueue.push({ chunk, meta });
							}
						}
					},
					error: (error) => {
						error.stack = stack; // Provide a more useful stack trace, the default one sucks
						this.error ??= error;
					},
				});
				this.encoder.configure(encoderConfig);

				if (this.encodingConfig.alpha === 'keep') {
					const stack = new Error('Encoding error').stack;

					// We need to encode alpha as well, which we do with a separate encoder
					this.alphaEncoder = new VideoEncoder({
						// We ignore the alpha chunk's metadata
						// eslint-disable-next-line @typescript-eslint/no-unused-vars
						output: (chunk, meta) => {
							alphaEncoderQueue--;

							// There has to be a color chunk because the encoders are wired in series
							const colorChunk = colorChunkQueue.shift();
							assert(colorChunk !== undefined);

							addPacket(colorChunk.chunk, chunk, colorChunk.meta);

							// See if there are any null alpha chunks queued up
							encodedAlphaChunkCount++;
							while (
								nullAlphaChunkQueue.length > 0
								&& nullAlphaChunkQueue[0] === encodedAlphaChunkCount
							) {
								nullAlphaChunkQueue.shift();
								const colorChunk = colorChunkQueue.shift();
								assert(colorChunk !== undefined);

								addPacket(colorChunk.chunk, null, colorChunk.meta);
							}
						},
						error: (error) => {
							error.stack = stack; // Provide a more useful stack trace
							this.error ??= error;
						},
					});
					this.alphaEncoder.configure(encoderConfig);
				}
			}

			assert(this.source._connectedTrack);
			this.muxer = this.source._connectedTrack.output._muxer;

			this.encoderInitialized = true;
		})();
	}

	async flushAndClose(forceClose: boolean) {
		if (!forceClose) {
			this.checkForEncoderError();
		}

		// Final frame rate padding: fill remaining frames up to the last sample's original end timestamp
		if (!forceClose && this.frameRateLastSample) {
			const frameRate = this.encodingConfig.transform!.frameRate!;
			const alignedEnd = floorToDivisor(this.frameRateLastEndTimestamp!, frameRate);
			await this.padFrameRate(alignedEnd);
		}

		this.frameRateLastSample?.close();
		this.frameRateLastSample = null;

		if (this.customEncoder) {
			if (!forceClose) {
				void this.customEncoderCallSerializer.call(() => this.customEncoder!.flush());
			}

			await this.customEncoderCallSerializer.call(() => this.customEncoder!.close());
		} else if (this.encoder) {
			if (!forceClose) {
				// These are wired in series, therefore they must also be flushed in series
				await this.encoder.flush();
				await this.alphaEncoder?.flush();
			}

			if (this.encoder.state !== 'closed') {
				this.encoder.close();
			}
			if (this.alphaEncoder && this.alphaEncoder.state !== 'closed') {
				this.alphaEncoder.close();
			}

			this.alphaFrameQueue.forEach(x => x?.close());

			this.splitter?.close();
		}

		if (!forceClose) {
			this.checkForEncoderError();
		}
	}

	getQueueSize() {
		if (this.customEncoder) {
			return this.customEncoderQueueSize;
		} else {
			// Because the color and alpha encoders are wired in series, there's no need to also include the alpha
			// encoder's queue size here
			return this.encoder?.encodeQueueSize ?? 0;
		}
	}

	checkForEncoderError() {
		if (this.error) {
			throw this.error;
		}
	}
}

let splitterGpuUnavailable = false;

/** Utility class for splitting a composite frame into separate color and alpha components. */
export class ColorAlphaSplitter {
	static forceCpu = true;

	canvas: OffscreenCanvas | HTMLCanvasElement | null = null;

	private gl: WebGL2RenderingContext | null = null;
	private colorProgram: WebGLProgram | null = null;
	private alphaProgram: WebGLProgram | null = null;
	private vao: WebGLVertexArrayObject | null = null;
	private sourceTexture: WebGLTexture | null = null;
	private alphaResolutionLocation: WebGLUniformLocation | null = null;

	private worker: Worker | null = null;
	private pendingRequests = new Map<
		number,
		ReturnType<typeof promiseWithResolvers<{ colorFrame: VideoFrame; alphaFrame: VideoFrame }>>
	>();

	private nextRequestId = 0;

	constructor(initialWidth: number, initialHeight: number) {
		const canMakeCanvas = typeof OffscreenCanvas !== 'undefined'
			// eslint-disable-next-line @typescript-eslint/no-deprecated
			|| (typeof document !== 'undefined' && typeof document.createElement === 'function');

		if (!ColorAlphaSplitter.forceCpu && canMakeCanvas && !splitterGpuUnavailable) {
			// Try the GPU path. If anything goes wrong, we silently fall back to the CPU path.
			try {
				if (typeof OffscreenCanvas !== 'undefined') {
					this.canvas = new OffscreenCanvas(initialWidth, initialHeight);
				} else {
					this.canvas = document.createElement('canvas');
					this.canvas.width = initialWidth;
					this.canvas.height = initialHeight;
				}

				const gl = this.canvas.getContext('webgl2', {
					alpha: true, // Needed due to the YUV thing we do for alpha
				}) as unknown as WebGL2RenderingContext | null; // Casting because of some TypeScript weirdness
				if (!gl) {
					throw new Error('Couldn\'t acquire WebGL 2 context.');
				}

				this.gl = gl;

				this.colorProgram = this.createColorProgram();
				this.alphaProgram = this.createAlphaProgram();
				this.vao = this.createVAO();
				this.sourceTexture = this.createTexture();

				this.alphaResolutionLocation = this.gl.getUniformLocation(this.alphaProgram, 'u_resolution')!;

				this.gl.useProgram(this.colorProgram);
				this.gl.uniform1i(this.gl.getUniformLocation(this.colorProgram, 'u_sourceTexture'), 0);

				this.gl.useProgram(this.alphaProgram);
				this.gl.uniform1i(this.gl.getUniformLocation(this.alphaProgram, 'u_sourceTexture'), 0);
			} catch (error) {
				this.gl = null;
				this.canvas = null;
				splitterGpuUnavailable = true;
				console.warn('Falling back to CPU for color/alpha splitting.', error);
			}
		}
	}

	async update(sourceFrame: VideoFrame) {
		if (this.gl) {
			return this.updateGpu(sourceFrame);
		} else {
			return this.updateCpu(sourceFrame);
		}
	}

	private updateGpu(sourceFrame: VideoFrame) {
		assert(this.gl);
		assert(this.canvas);

		if (sourceFrame.displayWidth !== this.canvas.width || sourceFrame.displayHeight !== this.canvas.height) {
			this.canvas.width = sourceFrame.displayWidth;
			this.canvas.height = sourceFrame.displayHeight;
		}

		this.gl.activeTexture(this.gl.TEXTURE0);
		this.gl.bindTexture(this.gl.TEXTURE_2D, this.sourceTexture);
		this.gl.texImage2D(this.gl.TEXTURE_2D, 0, this.gl.RGBA, this.gl.RGBA, this.gl.UNSIGNED_BYTE, sourceFrame);

		const colorFrame = this.runColorProgram(sourceFrame);
		const alphaFrame = this.runAlphaProgram(sourceFrame);

		sourceFrame.close();

		return { colorFrame, alphaFrame };
	}

	private createVertexShader(): WebGLShader {
		assert(this.gl);

		return this.createShader(this.gl.VERTEX_SHADER, `#version 300 es
			in vec2 a_position;
			in vec2 a_texCoord;
			out vec2 v_texCoord;
			
			void main() {
				gl_Position = vec4(a_position, 0.0, 1.0);
				v_texCoord = a_texCoord;
			}
		`);
	}

	private createColorProgram(): WebGLProgram {
		assert(this.gl);

		const vertexShader = this.createVertexShader();

		// This shader is simple, simply copy the color information while setting alpha to 1
		const fragmentShader = this.createShader(this.gl.FRAGMENT_SHADER, `#version 300 es
			precision highp float;
			
			uniform sampler2D u_sourceTexture;
			in vec2 v_texCoord;
			out vec4 fragColor;
			
			void main() {
				vec4 source = texture(u_sourceTexture, v_texCoord);
				fragColor = vec4(source.rgb, 1.0);
			}
		`);

		const program = this.gl.createProgram();
		this.gl.attachShader(program, vertexShader);
		this.gl.attachShader(program, fragmentShader);
		this.gl.linkProgram(program);

		return program;
	}

	private createAlphaProgram(): WebGLProgram {
		assert(this.gl);

		const vertexShader = this.createVertexShader();

		// This shader's more complex. The main reason is that this shader writes data in I420 (yuv420) pixel format
		// instead of regular RGBA. In other words, we use the shader to write out I420 data into an RGBA canvas, which
		// we then later read out with JavaScript. The reason being that browsers weirdly encode canvases and mess up
		// the color spaces, and the only way to have full control over the color space is by outputting YUV data
		// directly (avoiding the RGB conversion). Doing this conversion in JS is painfully slow, so let's utlize the
		// GPU since we're already calling it anyway.
		const fragmentShader = this.createShader(this.gl.FRAGMENT_SHADER, `#version 300 es
			precision highp float;
			
			uniform sampler2D u_sourceTexture;
			uniform vec2 u_resolution; // The width and height of the canvas
			in vec2 v_texCoord;
			out vec4 fragColor;

			// This function determines the value for a single byte in the YUV stream
			float getByteValue(float byteOffset) {
				float width = u_resolution.x;
				float height = u_resolution.y;

				float yPlaneSize = width * height;

				if (byteOffset < yPlaneSize) {
					// This byte is in the luma plane. Find the corresponding pixel coordinates to sample from
					float y = floor(byteOffset / width);
					float x = mod(byteOffset, width);
					
					// Add 0.5 to sample the center of the texel
					vec2 sampleCoord = (vec2(x, y) + 0.5) / u_resolution;
					
					// The luma value is the alpha from the source texture
					return texture(u_sourceTexture, sampleCoord).a;
				} else {
					// Write a fixed value for chroma and beyond
					return 128.0 / 255.0;
				}
			}
			
			void main() {
				// Each fragment writes 4 bytes (R, G, B, A)
				float pixelIndex = floor(gl_FragCoord.y) * u_resolution.x + floor(gl_FragCoord.x);
				float baseByteOffset = pixelIndex * 4.0;

				vec4 result;
				for (int i = 0; i < 4; i++) {
					float currentByteOffset = baseByteOffset + float(i);
					result[i] = getByteValue(currentByteOffset);
				}
				
				fragColor = result;
			}
		`);

		const program = this.gl.createProgram();
		this.gl.attachShader(program, vertexShader);
		this.gl.attachShader(program, fragmentShader);
		this.gl.linkProgram(program);

		return program;
	}

	private createShader(type: number, source: string): WebGLShader {
		assert(this.gl);

		const shader = this.gl.createShader(type)!;
		this.gl.shaderSource(shader, source);
		this.gl.compileShader(shader);
		if (!this.gl.getShaderParameter(shader, this.gl.COMPILE_STATUS)) {
			console.error('Shader compile error:', this.gl.getShaderInfoLog(shader));
		}
		return shader;
	}

	private createVAO(): WebGLVertexArrayObject {
		assert(this.gl);
		assert(this.colorProgram);

		const vao = this.gl.createVertexArray();
		this.gl.bindVertexArray(vao);

		const vertices = new Float32Array([
			-1, -1, 0, 1,
			1, -1, 1, 1,
			-1, 1, 0, 0,
			1, 1, 1, 0,
		]);

		const buffer = this.gl.createBuffer();
		this.gl.bindBuffer(this.gl.ARRAY_BUFFER, buffer);
		this.gl.bufferData(this.gl.ARRAY_BUFFER, vertices, this.gl.STATIC_DRAW);

		const positionLocation = this.gl.getAttribLocation(this.colorProgram, 'a_position');
		const texCoordLocation = this.gl.getAttribLocation(this.colorProgram, 'a_texCoord');

		this.gl.enableVertexAttribArray(positionLocation);
		this.gl.vertexAttribPointer(positionLocation, 2, this.gl.FLOAT, false, 16, 0);

		this.gl.enableVertexAttribArray(texCoordLocation);
		this.gl.vertexAttribPointer(texCoordLocation, 2, this.gl.FLOAT, false, 16, 8);

		return vao;
	}

	private createTexture(): WebGLTexture {
		assert(this.gl);

		const texture = this.gl.createTexture();

		this.gl.bindTexture(this.gl.TEXTURE_2D, texture);
		this.gl.texParameteri(this.gl.TEXTURE_2D, this.gl.TEXTURE_WRAP_S, this.gl.CLAMP_TO_EDGE);
		this.gl.texParameteri(this.gl.TEXTURE_2D, this.gl.TEXTURE_WRAP_T, this.gl.CLAMP_TO_EDGE);
		this.gl.texParameteri(this.gl.TEXTURE_2D, this.gl.TEXTURE_MIN_FILTER, this.gl.LINEAR);
		this.gl.texParameteri(this.gl.TEXTURE_2D, this.gl.TEXTURE_MAG_FILTER, this.gl.LINEAR);

		return texture;
	}

	private runColorProgram(sourceFrame: VideoFrame) {
		assert(this.gl);
		assert(this.canvas);

		this.gl.useProgram(this.colorProgram);
		this.gl.viewport(0, 0, this.canvas.width, this.canvas.height);
		this.gl.clear(this.gl.COLOR_BUFFER_BIT);
		this.gl.bindVertexArray(this.vao);
		this.gl.drawArrays(this.gl.TRIANGLE_STRIP, 0, 4);

		return new VideoFrame(this.canvas, {
			timestamp: sourceFrame.timestamp,
			duration: sourceFrame.duration ?? undefined,
			alpha: 'discard',
		});
	}

	private runAlphaProgram(sourceFrame: VideoFrame) {
		assert(this.gl);
		assert(this.canvas);

		this.gl.useProgram(this.alphaProgram);
		this.gl.uniform2f(this.alphaResolutionLocation, this.canvas.width, this.canvas.height);

		this.gl.viewport(0, 0, this.canvas.width, this.canvas.height);
		this.gl.clear(this.gl.COLOR_BUFFER_BIT);
		this.gl.bindVertexArray(this.vao);
		this.gl.drawArrays(this.gl.TRIANGLE_STRIP, 0, 4);

		const { width, height } = this.canvas;

		const chromaSamples = Math.ceil(width / 2) * Math.ceil(height / 2);
		const yuvSize = width * height + chromaSamples * 2;
		const requiredHeight = Math.ceil(yuvSize / (width * 4));

		let yuv = new Uint8Array(4 * width * requiredHeight);
		this.gl.readPixels(0, 0, width, requiredHeight, this.gl.RGBA, this.gl.UNSIGNED_BYTE, yuv);
		yuv = yuv.subarray(0, yuvSize);

		assert(yuv[width * height] === 128); // Where chroma data starts
		assert(yuv[yuv.length - 1] === 128); // Assert the YUV data has been fully written

		// Defining this separately because TypeScript doesn't know `transfer` and I can't be bothered to do declaration
		// merging right now
		const init = {
			format: 'I420' as const,
			codedWidth: width,
			codedHeight: height,
			timestamp: sourceFrame.timestamp,
			duration: sourceFrame.duration ?? undefined,
			transfer: [yuv.buffer],
		};
		return new VideoFrame(yuv, init);
	}

	private updateCpu(sourceFrame: VideoFrame): Promise<{ colorFrame: VideoFrame; alphaFrame: VideoFrame }> {
		if (!this.worker) {
			const blob = new Blob(
				[`(${colorAlphaSplitterWorkerCode.toString()})()`],
				{ type: 'application/javascript' },
			);
			const url = URL.createObjectURL(blob);
			this.worker = new Worker(url);
			URL.revokeObjectURL(url);

			this.worker.addEventListener('message', (event: MessageEvent<ColorAlphaSplitterWorkerResponse>) => {
				const data = event.data;
				const pending = this.pendingRequests.get(data.id);
				if (!pending) {
					return;
				}
				this.pendingRequests.delete(data.id);

				if ('error' in data) {
					pending.reject(new Error(data.error));
				} else {
					pending.resolve({ colorFrame: data.colorFrame, alphaFrame: data.alphaFrame });
				}
			});

			this.worker.addEventListener('error', (event) => {
				const error = new Error(event.message || 'Color/alpha splitter worker error.');
				for (const pending of this.pendingRequests.values()) {
					pending.reject(error);
				}
				this.pendingRequests.clear();
			});
		}

		const id = this.nextRequestId++;
		const pending = promiseWithResolvers<{ colorFrame: VideoFrame; alphaFrame: VideoFrame }>();
		this.pendingRequests.set(id, pending);
		this.worker.postMessage({ id, sourceFrame }, { transfer: [sourceFrame] });
		return pending.promise;
	}

	close() {
		this.gl?.getExtension('WEBGL_lose_context')?.loseContext();
		this.gl = null;
		this.canvas = null;

		this.worker?.terminate();
		this.worker = null;
		const error = new Error('Color/alpha splitter closed.');
		for (const pending of this.pendingRequests.values()) {
			pending.reject(error);
		}
		this.pendingRequests.clear();
	}
}

type ColorAlphaSplitterWorkerRequest = {
	id: number;
	sourceFrame: VideoFrame;
};

type ColorAlphaSplitterWorkerResponse =
	| { id: number; colorFrame: VideoFrame; alphaFrame: VideoFrame }
	| { id: number; error: string };

const colorAlphaSplitterWorkerCode = () => {
	// Reused across frames as long as the size matches, since consecutive frames usually share dimensions.
	let cpuSourceBuffer: Uint8Array | null = null;

	// Serialize execution internally so concurrent requests don't race on the shared cpuSourceBuffer.
	let chain: Promise<void> = Promise.resolve();
	self.addEventListener('message', (event: MessageEvent<ColorAlphaSplitterWorkerRequest>) => {
		const { id, sourceFrame } = event.data;
		chain = chain.then(async () => {
			try {
				const { colorFrame, alphaFrame } = await split(sourceFrame);
				self.postMessage({ id, colorFrame, alphaFrame }, { transfer: [colorFrame, alphaFrame] });
			} catch (error) {
				self.postMessage({ id, error: (error as Error).message });
			} finally {
				sourceFrame.close();
			}
		});
	});

	const split = async (sourceFrame: VideoFrame) => {
		const format = sourceFrame.format as VideoSamplePixelFormat | null;
		if (!format) {
			throw new Error('CPU color/alpha splitting requires a known VideoFrame format.');
		}

		const width = sourceFrame.codedWidth;
		const height = sourceFrame.codedHeight;
		const sourceSize = sourceFrame.allocationSize();

		if (!cpuSourceBuffer || cpuSourceBuffer.byteLength !== sourceSize) {
			cpuSourceBuffer = new Uint8Array(sourceSize);
		}
		await sourceFrame.copyTo(cpuSourceBuffer);

		if (format === 'RGBA' || format === 'BGRA') {
			return splitInterleavedRgba(cpuSourceBuffer, width, height, format, sourceFrame);
		} else if (
			format === 'I420A' || format === 'I420AP10' || format === 'I420AP12'
			|| format === 'I422A' || format === 'I422AP10' || format === 'I422AP12'
			|| format === 'I444A' || format === 'I444AP10' || format === 'I444AP12'
		) {
			return splitPlanarYuvA(cpuSourceBuffer, width, height, format, sourceFrame);
		}

		throw new Error(`CPU color/alpha splitting does not support format '${format}'.`);
	};

	const splitInterleavedRgba = (
		source: Uint8Array,
		width: number,
		height: number,
		format: 'RGBA' | 'BGRA',
		sourceFrame: VideoFrame,
	) => {
		const pixelCount = width * height;
		const chromaW = Math.ceil(width / 2);
		const chromaH = Math.ceil(height / 2);
		const alphaSize = pixelCount + chromaW * chromaH * 2;

		// Encode alpha as I420: Y = source A bytes, UV = 128
		const alphaBuffer = new Uint8Array(alphaSize);
		for (let i = 0, j = 3; i < pixelCount; i++, j += 4) {
			alphaBuffer[i] = source[j]!;
		}
		alphaBuffer.fill(128, pixelCount);

		// Hand the source buffer straight to VideoFrame as RGBX/BGRX so the A bytes are ignored
		const colorFrame = new VideoFrame(source, {
			format: format === 'RGBA' ? 'RGBX' : 'BGRX',
			codedWidth: width,
			codedHeight: height,
			timestamp: sourceFrame.timestamp,
			duration: sourceFrame.duration ?? undefined,
			// No transfer!
		});
		const alphaInit = {
			format: 'I420' as const,
			codedWidth: width,
			codedHeight: height,
			timestamp: sourceFrame.timestamp,
			duration: sourceFrame.duration ?? undefined,
			transfer: [alphaBuffer.buffer],
		};
		const alphaFrame = new VideoFrame(alphaBuffer, alphaInit);
		return { colorFrame, alphaFrame };
	};

	const splitPlanarYuvA = (
		source: Uint8Array,
		width: number,
		height: number,
		format:
			| 'I420A' | 'I420AP10' | 'I420AP12'
			| 'I422A' | 'I422AP10' | 'I422AP12'
			| 'I444A' | 'I444AP10' | 'I444AP12',
		sourceFrame: VideoFrame,
	) => {
		const is10 = format.includes('P10');
		const is12 = format.includes('P12');
		const bytesPerSample = (is10 || is12) ? 2 : 1;

		let chromaW: number;
		let chromaH: number;
		if (format.startsWith('I420')) {
			chromaW = Math.ceil(width / 2);
			chromaH = Math.ceil(height / 2);
		} else if (format.startsWith('I422')) {
			chromaW = Math.ceil(width / 2);
			chromaH = height;
		} else {
			chromaW = width;
			chromaH = height;
		}

		const ySamples = width * height;
		const uvSamples = chromaW * chromaH;
		const yBytes = ySamples * bytesPerSample;
		const uvBytes = uvSamples * bytesPerSample;
		const aBytes = ySamples * bytesPerSample;

		const colorBytes = yBytes + uvBytes * 2;
		const colorFormat = format.replace('A', '') as VideoPixelFormat;

		const alphaChromaW = Math.ceil(width / 2);
		const alphaChromaH = Math.ceil(height / 2);
		const alphaUvSamples = alphaChromaW * alphaChromaH;
		const alphaUvBytes = alphaUvSamples * bytesPerSample;
		const alphaSize = aBytes + 2 * alphaUvBytes;
		const alphaBuffer = new Uint8Array(alphaSize);

		const aPlaneStart = colorBytes;
		alphaBuffer.set(source.subarray(aPlaneStart, aPlaneStart + aBytes), 0);

		// Fill UV planes with the neutral chroma value
		const uvOffset = aBytes;
		const neutralChroma = is10 ? 512 : (is12 ? 2048 : 128);

		if (bytesPerSample === 1) {
			alphaBuffer.fill(neutralChroma, uvOffset);
		} else {
			const uvView = new Uint16Array(alphaBuffer.buffer, uvOffset, 2 * alphaUvSamples);
			uvView.fill(neutralChroma);
		}

		const alphaFormat = (is10 ? 'I420P10' : (is12 ? 'I420P12' : 'I420')) as VideoPixelFormat;

		// Color frame is simply a prefix of the combined bytes
		const colorFrame = new VideoFrame(source.subarray(0, colorBytes), {
			format: colorFormat,
			codedWidth: width,
			codedHeight: height,
			timestamp: sourceFrame.timestamp,
			duration: sourceFrame.duration ?? undefined,
		});
		const alphaInit = {
			format: alphaFormat,
			codedWidth: width,
			codedHeight: height,
			timestamp: sourceFrame.timestamp,
			duration: sourceFrame.duration ?? undefined,
			transfer: [alphaBuffer.buffer],
		};
		const alphaFrame = new VideoFrame(alphaBuffer, alphaInit);
		return { colorFrame, alphaFrame };
	};
};

/**
 * This source can be used to add raw, unencoded video samples (frames) to an output video track. These frames will
 * automatically be encoded and then piped into the output.
 * @group Media sources
 * @public
 */
export class VideoSampleSource extends VideoSource {
	/** @internal */
	private _encoder: VideoEncoderWrapper;

	/**
	 * Creates a new {@link VideoSampleSource} whose samples are encoded according to the specified
	 * {@link VideoEncodingConfig}.
	 */
	constructor(encodingConfig: VideoEncodingConfig) {
		validateVideoEncodingConfig(encodingConfig);

		super(encodingConfig.codec);
		this._encoder = new VideoEncoderWrapper(this, encodingConfig);
	}

	/**
	 * Encodes a video sample (frame) and then adds it to the output.
	 *
	 * @returns A Promise that resolves once the output is ready to receive more samples. You should await this Promise
	 * to respect writer and encoder backpressure.
	 */
	add(videoSample: VideoSample, encodeOptions?: VideoEncoderEncodeOptions) {
		if (!(videoSample instanceof VideoSample)) {
			throw new TypeError('videoSample must be a VideoSample.');
		}

		return this._encoder.add(videoSample, false, encodeOptions);
	}

	/** @internal */
	override _flushAndClose(forceClose: boolean) {
		return this._encoder.flushAndClose(forceClose);
	}
}

/**
 * This source can be used to add video frames to the output track from a fixed canvas element. Since canvases are often
 * used for rendering, this source provides a convenient wrapper around {@link VideoSampleSource}.
 * @group Media sources
 * @public
 */
export class CanvasSource extends VideoSource {
	/** @internal */
	private _encoder: VideoEncoderWrapper;
	/** @internal */
	private _canvas: HTMLCanvasElement | OffscreenCanvas;

	/**
	 * Creates a new {@link CanvasSource} from a canvas element or `OffscreenCanvas` whose samples are encoded
	 * according to the specified {@link VideoEncodingConfig}.
	 */
	constructor(canvas: HTMLCanvasElement | OffscreenCanvas, encodingConfig: VideoEncodingConfig) {
		if (
			!(typeof HTMLCanvasElement !== 'undefined' && canvas instanceof HTMLCanvasElement)
			&& !(typeof OffscreenCanvas !== 'undefined' && canvas instanceof OffscreenCanvas)
		) {
			throw new TypeError('canvas must be an HTMLCanvasElement or OffscreenCanvas.');
		}
		validateVideoEncodingConfig(encodingConfig);

		super(encodingConfig.codec);
		this._encoder = new VideoEncoderWrapper(this, encodingConfig);
		this._canvas = canvas;
	}

	/**
	 * Captures the current canvas state as a video sample (frame), encodes it and adds it to the output.
	 *
	 * @param timestamp - The timestamp of the sample, in seconds.
	 * @param duration - The duration of the sample, in seconds.
	 *
	 * @returns A Promise that resolves once the output is ready to receive more samples. You should await this Promise
	 * to respect writer and encoder backpressure.
	 */
	add(timestamp: number, duration = 0, encodeOptions?: VideoEncoderEncodeOptions) {
		if (!Number.isFinite(timestamp) || timestamp < 0) {
			throw new TypeError('timestamp must be a non-negative number.');
		}
		if (!Number.isFinite(duration) || duration < 0) {
			throw new TypeError('duration must be a non-negative number.');
		}

		const sample = new VideoSample(this._canvas, { timestamp, duration });
		return this._encoder.add(sample, true, encodeOptions);
	}

	/** @internal */
	override _flushAndClose(forceClose: boolean) {
		return this._encoder.flushAndClose(forceClose);
	}
}

/**
 * Options for {@link MediaStreamVideoTrackSource}.
 * @group Media sources
 * @public
 */
export type MediaStreamVideoTrackSourceOptions = {
	/**
	 * The frame rate at which the underlying video track is sampled. Defaults to the frame rate specified in the
	 * track's [`MediaTrackSettings`](https://developer.mozilla.org/en-US/docs/Web/API/MediaTrackSettings). Set to
	 * `null` to only add a frame whenever the underlying track pushes one - this minimizes frame count but can
	 * lead to wildly irregular FPS.
	 */
	frameRate?: number | null;
	/**
	 * Controls the basis (zero point) for video frame timestamps.
	 *
	 * When set to `'synced-zero'`, timestamps will be relative to the first chunk of media from a `MediaStreamTrack`
	 * added to the {@link Output}.
	 *
	 * When set to `'zero'`, timestamps will be relative to the first video frame emitted by this source.
	 *
	 * When set to `'unix'`, timestamps will be relative to the Unix epoch, so clearly associated with a distinct point
	 * in time. Here, pausing via {@link MediaStreamVideoTrackSource.pause} will also create gaps in timestamps. Be sure
	 * to pair this mode with {@link BaseTrackMetadata.isRelativeToUnixEpoch}.
	 *
	 * Defaults to `'synced-zero'`.
	 */
	timestampBase?: 'synced-zero' | 'zero' | 'unix';
};

/**
 * Video source that encodes the frames of a
 * [`MediaStreamVideoTrack`](https://developer.mozilla.org/en-US/docs/Web/API/MediaStreamTrack) and pipes them into the
 * output. This is useful for capturing live or real-time data such as webcams or screen captures. Frames will
 * automatically start being captured once the connected {@link Output} is started, and will keep being captured until
 * the {@link Output} is finalized or this source is closed.
 * @group Media sources
 * @public
 */
export class MediaStreamVideoTrackSource extends VideoSource {
	/** @internal */
	private _options: MediaStreamVideoTrackSourceOptions;
	/** @internal */
	private _encoder: VideoEncoderWrapper;
	/** @internal */
	private _abortController: AbortController | null = null;
	/** @internal */
	private _track: MediaStreamVideoTrack;
	/** @internal */
	private _workerTrackId: number | null = null;
	/** @internal */
	private _workerListener: ((event: MessageEvent) => void) | null = null;
	/** @internal */
	private _promiseWithResolvers = promiseWithResolvers();
	/** @internal */
	private _errorPromiseAccessed = false;
	/** @internal */
	private _paused = false;
	/** @internal */
	private _lastVideoFrame: VideoFrame | null = null;
	/** @internal */
	private _timerHandle: UnthrottledTimerHandle | null = null;
	/** @internal */
	private _videoElement: HTMLVideoElement | null = null;

	/** A promise that rejects upon any error within this source. This promise never resolves. */
	get errorPromise() {
		this._errorPromiseAccessed = true;
		return this._promiseWithResolvers.promise;
	}

	/** Whether this source is currently paused as a result of calling `.pause()`. */
	get paused() {
		return this._paused;
	}

	/**
	 * Creates a new {@link MediaStreamVideoTrackSource} from a
	 * [`MediaStreamVideoTrack`](https://developer.mozilla.org/en-US/docs/Web/API/MediaStreamTrack), which will pull
	 * video samples from the stream in real time and encode them according to {@link VideoEncodingConfig}.
	 */
	constructor(
		track: MediaStreamVideoTrack,
		encodingConfig: VideoEncodingConfig,
		options: MediaStreamVideoTrackSourceOptions = {},
	) {
		if (!(track instanceof MediaStreamTrack) || track.kind !== 'video') {
			throw new TypeError('track must be a video MediaStreamTrack.');
		}
		validateVideoEncodingConfig(encodingConfig);
		if (typeof options !== 'object' || !options) {
			throw new TypeError('options must be an object.');
		}
		if (options.frameRate != null && (typeof options.frameRate !== 'number' || options.frameRate <= 0)) {
			throw new TypeError('options.frameRate, when provided, must be either a positive number or null.');
		}
		if (
			options.timestampBase !== undefined
			&& options.timestampBase !== 'synced-zero'
			&& options.timestampBase !== 'zero'
			&& options.timestampBase !== 'unix'
		) {
			throw new TypeError(
				'options.timestampBase, when provided, must be one of \'synced-zero\', \'zero\', or \'unix\'.',
			);
		}

		encodingConfig = {
			...encodingConfig,
			latencyMode: 'realtime',
		};

		super(encodingConfig.codec);

		this._options = options;
		this._encoder = new VideoEncoderWrapper(this, encodingConfig);
		this._track = track;
	}

	/** @internal */
	override async _start() {
		if (!this._errorPromiseAccessed) {
			console.warn(
				'Make sure not to ignore the `errorPromise` field on MediaStreamVideoTrackSource, so that any internal'
				+ ' errors get bubbled up properly.',
			);
		}

		const frameRate = this._options.frameRate !== undefined
			? this._options.frameRate
			: (this._track.getSettings().frameRate ?? null);

		this._abortController = new AbortController();

		let firstVideoFrameTimestamp: number | null = null;
		let lastFrameTime: number | null = null;
		let frameCount = 0;
		let errored = false;
		let lastSampleTimestamp: number | null = null;
		let timestampOffset = 0;

		const tick = () => {
			assert(frameRate !== null);

			if (!this._lastVideoFrame) {
				return;
			}

			assert(lastFrameTime !== null);
			assert(firstVideoFrameTimestamp !== null);

			const now = performance.now();

			// Add as many frames as warranted by the elapsed time.
			// > instead of >= intentionally because tick() is called before the _lastVideoFrame is changed
			while (now - lastFrameTime > 1000 / frameRate) {
				lastFrameTime += 1000 / frameRate;
				const timestamp = firstVideoFrameTimestamp + frameCount / frameRate;

				const frame = new VideoFrame(this._videoElement ?? this._lastVideoFrame, {
					timestamp: 1e6 * timestamp,
					duration: 1e6 / frameRate,
				});

				addVideoFrame(frame, now);
			}
		};

		if (frameRate !== null) {
			this._timerHandle = setIntervalUnthrottled(tick, 4); // Run it at 250 Hz
		}

		const onVideoFrame = (videoFrame: VideoFrame) => {
			if (frameRate === null) {
				addVideoFrame(videoFrame);
			} else {
				const now = performance.now();

				if (!this._lastVideoFrame) {
					addVideoFrame(videoFrame.clone(), now);
					lastFrameTime = now;
					this._lastVideoFrame = videoFrame;
				} else {
					tick();
					this._lastVideoFrame?.close();
					this._lastVideoFrame = videoFrame;
				}
			}
		};

		const addVideoFrame = (videoFrame: VideoFrame, now = performance.now()) => {
			if (errored) {
				videoFrame.close();
				return;
			}

			frameCount++;
			const currentTimestamp = videoFrame.timestamp / 1e6;

			if (this._paused) {
				const frameSeen = firstVideoFrameTimestamp !== null;
				if (frameSeen) {
					if (lastSampleTimestamp !== null && this._options.timestampBase !== 'unix') {
						// In addition to dropping this frame, let's also keep track of the time we have lost due to the
						// pause. Doing it like this instead of simply keeping track of the paused time is better since
						// it retains the frame rate of the underlying source.
						const timeDelta = currentTimestamp - lastSampleTimestamp;
						timestampOffset -= timeDelta;
					}
					lastSampleTimestamp = currentTimestamp;
				}

				videoFrame.close();
				return;
			}

			if (firstVideoFrameTimestamp === null) {
				firstVideoFrameTimestamp = currentTimestamp;

				let target: number;
				const timestampBase = this._options.timestampBase ?? 'synced-zero';
				if (timestampBase === 'unix') {
					target = Date.now() / 1000;
				} else if (timestampBase === 'zero') {
					target = 0;
				} else {
					const output = this._connectedTrack!.output;
					if (output._firstMediaStreamTimestamp === null) {
						output._firstMediaStreamTimestamp = now / 1000;
						target = 0;
					} else {
						target = now / 1000 - output._firstMediaStreamTimestamp;
					}
				}

				timestampOffset = target - firstVideoFrameTimestamp;
			}

			lastSampleTimestamp = currentTimestamp;

			if (this._encoder.getQueueSize() >= 8) {
				// Drop frames if the encoder is overloaded
				videoFrame.close();
				return;
			}

			const sample = new VideoSample(videoFrame, {
				timestamp: currentTimestamp + timestampOffset,
			});

			void this._encoder.add(sample, true)
				.catch((error) => {
					errored = true;

					this._abortController?.abort();
					this._promiseWithResolvers.reject(error);

					if (this._workerTrackId !== null) {
						// Tell the worker to stop the track
						sendMessageToMediaStreamTrackProcessorWorker({
							type: 'stopTrack',
							trackId: this._workerTrackId,
						});
					}
				});
		};

		if (typeof MediaStreamTrackProcessor !== 'undefined') {
			// We can do it here directly, perfect
			const processor = new MediaStreamTrackProcessor({ track: this._track });
			const consumer = new WritableStream<VideoFrame>({ write: onVideoFrame });

			processor.readable.pipeTo(consumer, {
				signal: this._abortController.signal,
			}).catch((error) => {
				// Handle AbortError silently
				if (error instanceof DOMException && error.name === 'AbortError') return;

				this._promiseWithResolvers.reject(error);
			});
		} else {
			// It might still be supported in a worker, so let's check that
			const supportedInWorker = await mediaStreamTrackProcessorIsSupportedInWorker();

			if (supportedInWorker) {
				this._workerTrackId = nextMediaStreamTrackProcessorWorkerId++;

				sendMessageToMediaStreamTrackProcessorWorker({
					type: 'videoTrack',
					trackId: this._workerTrackId,
					track: this._track,
				});

				this._workerListener = (event: MessageEvent) => {
					const message = event.data as MediaStreamTrackProcessorWorkerMessage;

					if (message.type === 'videoFrame' && message.trackId === this._workerTrackId) {
						onVideoFrame(message.videoFrame);
					} else if (message.type === 'error' && message.trackId === this._workerTrackId) {
						this._promiseWithResolvers.reject(message.error);
					}
				};

				mediaStreamTrackProcessorWorker!.addEventListener('message', this._workerListener);
			} else if (frameRate !== null) {
				// No MediaStreamTrackProcessor support at all (e.g. Firefox), but we have a frame rate, so we can
				// manually sample from a hidden <video> element instead.
				const video = document.createElement('video');
				video.style.position = 'fixed';
				video.style.left = '-10000px';
				video.style.top = '-10000px';
				video.style.width = '1px';
				video.style.height = '1px';
				video.style.opacity = '0';
				video.style.pointerEvents = 'none';
				video.muted = true;
				video.srcObject = new MediaStream([this._track]);
				document.body.appendChild(video);
				this._videoElement = video;

				video.addEventListener('loadeddata', () => {
					if (errored || !this._videoElement) {
						return;
					}

					// This will be the first frame
					const frame = new VideoFrame(video, {
						timestamp: 1000 * performance.now(),
					});
					onVideoFrame(frame);
					frame.close();
				}, { once: true });

				void video.play().catch((error) => {
					errored = true;
					this._promiseWithResolvers.reject(error);
				});
			} else {
				throw new Error(
					'When no explicit frame rate is set, MediaStreamTrackProcessor is required; but it\'s not supported'
					+ ' by this browser.',
				);
			}
		}
	}

	/**
	 * Pauses the capture of video frames - any video frames emitted by the underlying media stream will be ignored
	 * while paused. This does *not* close the underlying `MediaStreamVideoTrack`, it just ignores its output.
	 */
	pause() {
		this._paused = true;
	}

	/** Resumes the capture of video frames after being paused. */
	resume() {
		this._paused = false;
	}

	/** @internal */
	override async _flushAndClose(forceClose: boolean) {
		if (this._abortController) {
			this._abortController.abort();
			this._abortController = null;
		}

		if (this._timerHandle) {
			clearIntervalUnthrottled(this._timerHandle);
		}
		this._lastVideoFrame?.close();

		if (this._videoElement) {
			this._videoElement.srcObject = null;
			this._videoElement.remove();
			this._videoElement = null;
		}

		if (this._workerTrackId !== null) {
			assert(this._workerListener);

			sendMessageToMediaStreamTrackProcessorWorker({
				type: 'stopTrack',
				trackId: this._workerTrackId,
			});

			// Wait for the worker to stop the track
			await new Promise<void>((resolve) => {
				const listener = (event: MessageEvent) => {
					const message = event.data as MediaStreamTrackProcessorWorkerMessage;

					if (message.type === 'trackStopped' && message.trackId === this._workerTrackId) {
						assert(this._workerListener);
						mediaStreamTrackProcessorWorker!.removeEventListener('message', this._workerListener);
						mediaStreamTrackProcessorWorker!.removeEventListener('message', listener);

						resolve();
					}
				};

				mediaStreamTrackProcessorWorker!.addEventListener('message', listener);
			});
		}

		await this._encoder.flushAndClose(forceClose);
	}
}

/**
 * Base class for audio sources - sources for audio tracks.
 * @group Media sources
 * @public
 */
export abstract class AudioSource extends MediaSource {
	/** @internal */
	override _connectedTrack: OutputAudioTrack | null = null;
	/** @internal */
	override readonly _codec: AudioCodec;

	/** Internal constructor. */
	constructor(codec: AudioCodec) {
		super();

		if (!AUDIO_CODECS.includes(codec)) {
			throw new TypeError(`Invalid audio codec '${codec}'. Must be one of: ${AUDIO_CODECS.join(', ')}.`);
		}

		this._codec = codec;
	}
}

/**
 * The most basic audio source; can be used to directly pipe encoded packets into the output file.
 * @group Media sources
 * @public
 */
export class EncodedAudioPacketSource extends AudioSource {
	/** Creates a new {@link EncodedAudioPacketSource} whose packets are encoded using `codec`. */
	constructor(codec: AudioCodec) {
		super(codec);
	}

	/**
	 * Adds an encoded packet to the output audio track. Packets must be added in *decode order*.
	 *
	 * @param meta - Additional metadata from the encoder. You should pass this for the first call, including a valid
	 * decoder config.
	 *
	 * @returns A Promise that resolves once the output is ready to receive more samples. You should await this Promise
	 * to respect writer and encoder backpressure.
	 */
	add(packet: EncodedPacket, meta?: EncodedAudioChunkMetadata) {
		if (!(packet instanceof EncodedPacket)) {
			throw new TypeError('packet must be an EncodedPacket.');
		}
		if (packet.isMetadataOnly) {
			throw new TypeError('Metadata-only packets cannot be added.');
		}
		if (meta !== undefined && (!meta || typeof meta !== 'object')) {
			throw new TypeError('meta, when provided, must be an object.');
		}

		this._ensureValidAdd();
		return this._connectedTrack!.output._muxer.addEncodedAudioPacket(this._connectedTrack!, packet, meta);
	}
}

class AudioEncoderWrapper {
	private ensureEncoderPromise: Promise<void> | null = null;
	private encoderInitialized = false;
	private encoder: AudioEncoder | null = null;
	private muxer: Muxer | null = null;
	private lastNumberOfChannels: number | null = null;
	private lastSampleRate: number | null = null;

	private isPcmEncoder = false;
	private outputSampleSize: number | null = null;
	private writeOutputValue: ((view: DataView, byteOffset: number, value: number) => void) | null = null;

	private customEncoder: CustomAudioEncoder | null = null;
	private customEncoderCallSerializer = new CallSerializer();
	private customEncoderQueueSize = 0;

	private lastEndSampleIndex: number | null = null;

	private resampler: AudioResampler | null = null;

	/**
	 * Encoders typically throw their errors "out of band", meaning asynchronously in some other execution context.
	 * However, we want to surface these errors to the user within the normal control flow, so they don't go uncaught.
	 * So, we keep track of the encoder error and throw it as soon as we get the chance.
	 */
	private error: Error | null = null;
	private lastMuxerPromise: Promise<void> = Promise.resolve();

	constructor(private source: AudioSource, private encodingConfig: AudioEncodingConfig) {}

	async add(audioSample: AudioSample, shouldClose: boolean) {
		try {
			this.checkForEncoderError();
			this.source._ensureValidAdd();

			// Ensure audio parameters remain constant
			if (this.lastNumberOfChannels !== null && this.lastSampleRate !== null) {
				if (
					audioSample.numberOfChannels !== this.lastNumberOfChannels
					|| audioSample.sampleRate !== this.lastSampleRate
				) {
					throw new Error(
						`Audio parameters must remain constant. Expected ${this.lastNumberOfChannels} channels at`
						+ ` ${this.lastSampleRate} Hz, got ${audioSample.numberOfChannels} channels at`
						+ ` ${audioSample.sampleRate} Hz.`,
					);
				}
			} else {
				this.lastNumberOfChannels = audioSample.numberOfChannels;
				this.lastSampleRate = audioSample.sampleRate;
			}

			const config = this.encodingConfig;
			const needsResample = config.transform?.numberOfChannels !== undefined
				|| config.transform?.sampleRate !== undefined;

			if (needsResample) {
				if (!this.resampler) {
					// Initialize the resampler on first sample
					this.resampler = new AudioResampler({
						targetNumberOfChannels: config.transform!.numberOfChannels
							?? audioSample.numberOfChannels,
						targetSampleRate: config.transform!.sampleRate
							?? audioSample.sampleRate,
						startTime: audioSample.timestamp,
						endTime: Infinity,
						onSample: async (sample) => {
							await this.processAndEncode(sample, true);
						},
					});
				}

				await this.resampler.add(audioSample);
			} else {
				await this.processAndEncode(audioSample, shouldClose);
			}
		} finally {
			if (shouldClose) {
				audioSample.close();
			}
		}
	}

	/**
	 * Runs the process function (if any) and encodes the resulting samples.
	 */
	private async processAndEncode(audioSample: AudioSample, shouldClose: boolean) {
		const config = this.encodingConfig;

		if (
			config.transform?.sampleFormat !== undefined
			&& toInterleavedAudioFormat(audioSample.format) !== config.transform.sampleFormat
		) {
			// Do a sample format conversion
			const newSample = audioSampleToInterleavedFormat(audioSample, config.transform.sampleFormat);

			if (shouldClose) {
				audioSample.close();
			}

			audioSample = newSample;
			shouldClose = true;
		}

		if (config.transform?.process) {
			let processed = config.transform.process(audioSample);
			if (processed instanceof Promise) {
				processed = await processed;
			}

			if (processed === null) {
				return;
			}

			if (!Array.isArray(processed)) {
				processed = [processed];
			}

			for (const sample of processed) {
				if (!(sample instanceof AudioSample)) {
					throw new TypeError(
						'The audio process function must return an AudioSample, null, or an array of AudioSamples.',
					);
				}
				await this.encodeSample(sample, true);
			}

			if (shouldClose) {
				audioSample.close();
			}
		} else {
			await this.encodeSample(audioSample, shouldClose);
		}
	}

	/**
	 * Encodes a single audio sample, handling encoder init, gap padding, and backpressure.
	 */
	private async encodeSample(audioSample: AudioSample, shouldClose: boolean) {
		try {
			if (!this.encoderInitialized) {
				if (!this.ensureEncoderPromise) {
					this.ensureEncoder(audioSample);
				}

				// No, this "if" statement is not useless. Sometimes, the above call to `ensureEncoder` might have
				// synchronously completed and the encoder is already initialized. In this case, we don't need to await
				// the promise anymore. This also fixes nasty async race condition bugs when multiple code paths are
				// calling this method: It's important that the call that initialized the encoder go through this
				// code first.
				if (!this.encoderInitialized) {
					await this.ensureEncoderPromise;
				}
			}
			assert(this.encoderInitialized);

			// Handle padding of gaps with silence to avoid audio drift over time, like in
			// https://github.com/Vanilagy/mediabunny/issues/176
			// TODO An open question is how encoders deal with the first AudioData having a non-zero timestamp, and with
			// AudioDatas that have an overlapping timestamp range.
			{
				const startSampleIndex = Math.round(
					audioSample.timestamp * audioSample.sampleRate,
				);
				const endSampleIndex = Math.round(
					(audioSample.timestamp + audioSample.duration) * audioSample.sampleRate,
				);

				if (this.lastEndSampleIndex === null) {
					this.lastEndSampleIndex = endSampleIndex;
				} else {
					const sampleDiff = startSampleIndex - this.lastEndSampleIndex;

					if (sampleDiff >= 64) {
						// The gap is big enough, let's add a correction sample
						const fillSample = new AudioSample({
							data: new Float32Array(sampleDiff * audioSample.numberOfChannels),
							format: 'f32-planar',
							sampleRate: audioSample.sampleRate,
							numberOfChannels: audioSample.numberOfChannels,
							numberOfFrames: sampleDiff,
							timestamp: this.lastEndSampleIndex / audioSample.sampleRate,
						});

						await this.encodeSample(fillSample, true); // Recursive call
					}

					this.lastEndSampleIndex += audioSample.numberOfFrames;
				}
			}

			if (this.customEncoder) {
				this.customEncoderQueueSize++;

				// We clone the sample so it cannot be closed on us from the outside before it reaches the encoder
				const clonedSample = audioSample.clone();

				const promise = this.customEncoderCallSerializer
					.call(() => this.customEncoder!.encode(clonedSample))
					.then(() => this.customEncoderQueueSize--)
					.catch((error: Error) => this.error ??= error)
					.finally(() => {
						clonedSample.close();
					});

				if (this.customEncoderQueueSize >= 4) {
					await promise;
				}

				await this.lastMuxerPromise; // Allow the writer to apply backpressure
			} else if (this.isPcmEncoder) {
				await this.doPcmEncoding(audioSample, shouldClose);
			} else {
				assert(this.encoder);
				const audioData = audioSample.toAudioData();
				this.encoder.encode(audioData);
				audioData.close();

				if (shouldClose) {
					audioSample.close();
				}

				if (this.encoder.encodeQueueSize >= 4) {
					await new Promise(resolve => this.encoder!.addEventListener('dequeue', resolve, { once: true }));
				}

				await this.lastMuxerPromise; // Allow the writer to apply backpressure
			}
		} finally {
			if (shouldClose) {
				audioSample.close();
			}
		}
	}

	private async doPcmEncoding(audioSample: AudioSample, shouldClose: boolean) {
		assert(this.outputSampleSize);
		assert(this.writeOutputValue);

		// Need to extract data from the audio data before we close it
		const { numberOfChannels, numberOfFrames, sampleRate, timestamp } = audioSample;

		const CHUNK_SIZE = 2048;
		const outputs: {
			frameCount: number;
			view: DataView;
		}[] = [];

		// Prepare all of the output buffers, each being bounded by CHUNK_SIZE so we don't generate huge packets
		for (let frame = 0; frame < numberOfFrames; frame += CHUNK_SIZE) {
			const frameCount = Math.min(CHUNK_SIZE, audioSample.numberOfFrames - frame);
			const outputSize = frameCount * numberOfChannels * this.outputSampleSize;
			const outputBuffer = new ArrayBuffer(outputSize);
			const outputView = new DataView(outputBuffer);

			outputs.push({ frameCount, view: outputView });
		}

		const allocationSize = audioSample.allocationSize(({ planeIndex: 0, format: 'f32-planar' }));
		const floats = new Float32Array(allocationSize / Float32Array.BYTES_PER_ELEMENT);

		for (let i = 0; i < numberOfChannels; i++) {
			audioSample.copyTo(floats, { planeIndex: i, format: 'f32-planar' });

			for (let j = 0; j < outputs.length; j++) {
				const { frameCount, view } = outputs[j]!;

				for (let k = 0; k < frameCount; k++) {
					this.writeOutputValue(
						view,
						(k * numberOfChannels + i) * this.outputSampleSize,
						floats[j * CHUNK_SIZE + k]!,
					);
				}
			}
		}

		if (shouldClose) {
			audioSample.close();
		}

		const meta: EncodedAudioChunkMetadata = {
			decoderConfig: {
				codec: this.encodingConfig.codec,
				numberOfChannels,
				sampleRate,
			},
		};

		for (let i = 0; i < outputs.length; i++) {
			const { frameCount, view } = outputs[i]!;
			const outputBuffer = view.buffer;
			const startFrame = i * CHUNK_SIZE;

			const packet = new EncodedPacket(
				new Uint8Array(outputBuffer),
				'key',
				timestamp + startFrame / sampleRate,
				frameCount / sampleRate,
			);

			this.encodingConfig.onEncodedPacket?.(packet, meta);
			await this.muxer!.addEncodedAudioPacket(this.source._connectedTrack!, packet, meta); // With backpressure
		}
	}

	private ensureEncoder(audioSample: AudioSample) {
		this.ensureEncoderPromise = (async () => {
			const { numberOfChannels, sampleRate } = audioSample;

			const encoderConfig = buildAudioEncoderConfig({
				numberOfChannels,
				sampleRate,
				...this.encodingConfig,
			});
			this.encodingConfig.onEncoderConfig?.(encoderConfig);

			const MatchingCustomEncoder = customAudioEncoders.find(x => x.supports(
				this.encodingConfig.codec,
				encoderConfig,
			));

			if (MatchingCustomEncoder) {
				// @ts-expect-error "Can't create instance of abstract class 🤓"
				this.customEncoder = new MatchingCustomEncoder() as CustomAudioEncoder;
				// @ts-expect-error It's technically readonly
				this.customEncoder.codec = this.encodingConfig.codec;
				// @ts-expect-error It's technically readonly
				this.customEncoder.config = encoderConfig;
				// @ts-expect-error It's technically readonly
				this.customEncoder.onPacket = (packet, meta) => {
					if (!(packet instanceof EncodedPacket)) {
						throw new TypeError('The first argument passed to onPacket must be an EncodedPacket.');
					}
					if (meta !== undefined && (!meta || typeof meta !== 'object')) {
						throw new TypeError('The second argument passed to onPacket must be an object or undefined.');
					}

					this.encodingConfig.onEncodedPacket?.(packet, meta);
					this.lastMuxerPromise
						= this.muxer!.addEncodedAudioPacket(this.source._connectedTrack!, packet, meta)
							.catch((error) => {
								this.error ??= error;
							});
				};

				await this.customEncoder.init();
			} else if ((PCM_AUDIO_CODECS as readonly string[]).includes(this.encodingConfig.codec)) {
				this.initPcmEncoder();
			} else {
				if (typeof AudioEncoder === 'undefined') {
					throw new Error('AudioEncoder is not supported by this browser.');
				}

				const support = await AudioEncoder.isConfigSupported(encoderConfig);
				if (!support.supported) {
					throw new Error(
						`This specific encoder configuration (${encoderConfig.codec}, ${encoderConfig.bitrate} bps,`
						+ ` ${encoderConfig.numberOfChannels} channels, ${encoderConfig.sampleRate} Hz) is not`
						+ ` supported by this browser. Consider using another codec or changing your audio parameters.`,
					);
				}

				const stack = new Error('Encoding error').stack;

				this.encoder = new AudioEncoder({
					output: (chunk, meta) => {
						// WebKit emits an invalid description for AAC (https://bugs.webkit.org/show_bug.cgi?id=302253),
						// which we try to detect here. If detected, we'll provide our own description instead, derived
						// from the codec string and audio parameters.
						if (this.encodingConfig.codec === 'aac' && meta?.decoderConfig) {
							let needsDescriptionOverwrite = false;
							if (!meta.decoderConfig.description || meta.decoderConfig.description.byteLength < 2) {
								needsDescriptionOverwrite = true;
							} else {
								const audioSpecificConfig = parseAacAudioSpecificConfig(
									toUint8Array(meta.decoderConfig.description),
								);

								needsDescriptionOverwrite = audioSpecificConfig.objectType === 0;
							}

							if (needsDescriptionOverwrite) {
								const objectType = Number(last(encoderConfig.codec.split('.')));

								meta.decoderConfig.description = buildAacAudioSpecificConfig({
									objectType,
									numberOfChannels: meta.decoderConfig.numberOfChannels,
									sampleRate: meta.decoderConfig.sampleRate,
								});
							}
						}

						let packet = EncodedPacket.fromEncodedChunk(chunk);

						// Snap the timing information to the sample rate to recover information lost in microsecond
						// conversion
						packet = packet.clone({
							timestamp: roundToDivisor(packet.timestamp, encoderConfig.sampleRate),
							duration: chunk.duration != null
								? roundToDivisor(packet.duration, encoderConfig.sampleRate)
								: undefined,
						});

						this.encodingConfig.onEncodedPacket?.(packet, meta);
						this.lastMuxerPromise
							= this.muxer!.addEncodedAudioPacket(this.source._connectedTrack!, packet, meta)
								.catch((error) => {
									this.error ??= error;
								});
					},
					error: (error) => {
						error.stack = stack; // Provide a more useful stack trace
						this.error ??= error;
					},
				});
				this.encoder.configure(encoderConfig);
			}

			assert(this.source._connectedTrack);
			this.muxer = this.source._connectedTrack.output._muxer;

			this.encoderInitialized = true;
		})();
	}

	private initPcmEncoder() {
		this.isPcmEncoder = true;

		const codec = this.encodingConfig.codec as PcmAudioCodec;
		const { dataType, sampleSize, littleEndian } = parsePcmCodec(codec);

		this.outputSampleSize = sampleSize;

		// All these functions receive a float sample as input and map it into the desired format

		switch (sampleSize) {
			case 1: {
				if (dataType === 'unsigned') {
					this.writeOutputValue = (view, byteOffset, value) =>
						view.setUint8(byteOffset, clamp((value + 1) * 127.5, 0, 255));
				} else if (dataType === 'signed') {
					this.writeOutputValue = (view, byteOffset, value) => {
						view.setInt8(byteOffset, clamp(Math.round(value * 128), -128, 127));
					};
				} else if (dataType === 'ulaw') {
					this.writeOutputValue = (view, byteOffset, value) => {
						const int16 = clamp(Math.floor(value * 32767), -32768, 32767);
						view.setUint8(byteOffset, toUlaw(int16));
					};
				} else if (dataType === 'alaw') {
					this.writeOutputValue = (view, byteOffset, value) => {
						const int16 = clamp(Math.floor(value * 32767), -32768, 32767);
						view.setUint8(byteOffset, toAlaw(int16));
					};
				} else {
					assert(false);
				}
			}; break;
			case 2: {
				if (dataType === 'unsigned') {
					this.writeOutputValue = (view, byteOffset, value) =>
						view.setUint16(byteOffset, clamp((value + 1) * 32767.5, 0, 65535), littleEndian);
				} else if (dataType === 'signed') {
					this.writeOutputValue = (view, byteOffset, value) =>
						view.setInt16(byteOffset, clamp(Math.round(value * 32767), -32768, 32767), littleEndian);
				} else {
					assert(false);
				}
			}; break;
			case 3: {
				if (dataType === 'unsigned') {
					this.writeOutputValue = (view, byteOffset, value) =>
						setUint24(view, byteOffset, clamp((value + 1) * 8388607.5, 0, 16777215), littleEndian);
				} else if (dataType === 'signed') {
					this.writeOutputValue = (view, byteOffset, value) =>
						setInt24(
							view,
							byteOffset,
							clamp(Math.round(value * 8388607), -8388608, 8388607),
							littleEndian,
						);
				} else {
					assert(false);
				}
			}; break;
			case 4: {
				if (dataType === 'unsigned') {
					this.writeOutputValue = (view, byteOffset, value) =>
						view.setUint32(byteOffset, clamp((value + 1) * 2147483647.5, 0, 4294967295), littleEndian);
				} else if (dataType === 'signed') {
					this.writeOutputValue = (view, byteOffset, value) =>
						view.setInt32(
							byteOffset,
							clamp(Math.round(value * 2147483647), -2147483648, 2147483647),
							littleEndian,
						);
				} else if (dataType === 'float') {
					this.writeOutputValue = (view, byteOffset, value) =>
						view.setFloat32(byteOffset, value, littleEndian);
				} else {
					assert(false);
				}
			}; break;
			case 8: {
				if (dataType === 'float') {
					this.writeOutputValue = (view, byteOffset, value) =>
						view.setFloat64(byteOffset, value, littleEndian);
				} else {
					assert(false);
				}
			}; break;
			default: {
				assertNever(sampleSize);
				assert(false);
			};
		}
	}

	async flushAndClose(forceClose: boolean) {
		if (!forceClose) {
			this.checkForEncoderError();
		}

		// Finalize the resampler to flush any buffered audio
		if (!forceClose && this.resampler) {
			await this.resampler.finalize();
		}
		this.resampler = null;

		if (this.customEncoder) {
			if (!forceClose) {
				void this.customEncoderCallSerializer.call(() => this.customEncoder!.flush());
			}

			await this.customEncoderCallSerializer.call(() => this.customEncoder!.close());
		} else if (this.encoder) {
			if (!forceClose) {
				await this.encoder.flush();
			}

			if (this.encoder.state !== 'closed') {
				this.encoder.close();
			}
		}

		if (!forceClose) {
			this.checkForEncoderError();
		}
	}

	getQueueSize() {
		if (this.customEncoder) {
			return this.customEncoderQueueSize;
		} else if (this.isPcmEncoder) {
			return 0;
		} else {
			return this.encoder?.encodeQueueSize ?? 0;
		}
	}

	checkForEncoderError() {
		if (this.error) {
			throw this.error;
		}
	}
}

/**
 * This source can be used to add raw, unencoded audio samples to an output audio track. These samples will
 * automatically be encoded and then piped into the output.
 * @group Media sources
 * @public
 */
export class AudioSampleSource extends AudioSource {
	/** @internal */
	private _encoder: AudioEncoderWrapper;

	/**
	 * Creates a new {@link AudioSampleSource} whose samples are encoded according to the specified
	 * {@link AudioEncodingConfig}.
	 */
	constructor(encodingConfig: AudioEncodingConfig) {
		validateAudioEncodingConfig(encodingConfig);

		super(encodingConfig.codec);
		this._encoder = new AudioEncoderWrapper(this, encodingConfig);
	}

	/**
	 * Encodes an audio sample and then adds it to the output.
	 *
	 * @returns A Promise that resolves once the output is ready to receive more samples. You should await this Promise
	 * to respect writer and encoder backpressure.
	 */
	add(audioSample: AudioSample) {
		if (!(audioSample instanceof AudioSample)) {
			throw new TypeError('audioSample must be an AudioSample.');
		}

		return this._encoder.add(audioSample, false);
	}

	/** @internal */
	override _flushAndClose(forceClose: boolean) {
		return this._encoder.flushAndClose(forceClose);
	}
}

/**
 * This source can be used to add audio data from an AudioBuffer to the output track. This is useful when working with
 * the Web Audio API.
 * @group Media sources
 * @public
 */
export class AudioBufferSource extends AudioSource {
	/** @internal */
	private _encoder: AudioEncoderWrapper;
	/** @internal */
	private _accumulatedTime = 0;

	/**
	 * Creates a new {@link AudioBufferSource} whose `AudioBuffer` instances are encoded according to the specified
	 * {@link AudioEncodingConfig}.
	 */
	constructor(encodingConfig: AudioEncodingConfig) {
		validateAudioEncodingConfig(encodingConfig);

		super(encodingConfig.codec);
		this._encoder = new AudioEncoderWrapper(this, encodingConfig);
	}

	/**
	 * Converts an AudioBuffer to audio samples, encodes them and adds them to the output. The first AudioBuffer will
	 * be played at timestamp 0, and any subsequent AudioBuffer will have a timestamp equal to the total duration of
	 * all previous AudioBuffers.
	 *
	 * @returns A Promise that resolves once the output is ready to receive more samples. You should await this Promise
	 * to respect writer and encoder backpressure.
	 */
	async add(audioBuffer: AudioBuffer) {
		if (!(audioBuffer instanceof AudioBuffer)) {
			throw new TypeError('audioBuffer must be an AudioBuffer.');
		}

		const iterator = AudioSample._fromAudioBuffer(audioBuffer, this._accumulatedTime);
		this._accumulatedTime += audioBuffer.duration;

		for (const audioSample of iterator) {
			await this._encoder.add(audioSample, true);
		}
	}

	/** @internal */
	override _flushAndClose(forceClose: boolean) {
		return this._encoder.flushAndClose(forceClose);
	}
}

/**
 * Options for {@link MediaStreamAudioTrackSource}.
 * @group Media sources
 * @public
 */
export type MediaStreamAudioTrackSourceOptions = {
	/**
	 * Controls the basis (zero point) for audio sample timestamps.
	 *
	 * When set to `'synced-zero'`, timestamps will be relative to the first chunk of media from a `MediaStreamTrack`
	 * added to the {@link Output}.
	 *
	 * When set to `'zero'`, timestamps will be relative to the first audio sample emitted by this source.
	 *
	 * When set to `'unix'`, timestamps will be relative to the Unix epoch, so clearly associated with a distinct point
	 * in time. Here, pausing via {@link MediaStreamAudioTrackSource.pause} will also create gaps in timestamps. Be sure
	 * to pair this mode with {@link BaseTrackMetadata.isRelativeToUnixEpoch}.
	 *
	 * Defaults to `'synced-zero'`.
	 */
	timestampBase?: 'synced-zero' | 'zero' | 'unix';
};

/**
 * Audio source that encodes the data of a
 * [`MediaStreamAudioTrack`](https://developer.mozilla.org/en-US/docs/Web/API/MediaStreamTrack) and pipes it into the
 * output. This is useful for capturing live or real-time audio such as microphones or audio from other media elements.
 * Audio will automatically start being captured once the connected {@link Output} is started, and will keep being
 * captured until the {@link Output} is finalized or this source is closed.
 * @group Media sources
 * @public
 */
export class MediaStreamAudioTrackSource extends AudioSource {
	/** @internal */
	private _options: MediaStreamAudioTrackSourceOptions;
	/** @internal */
	private _encoder: AudioEncoderWrapper;
	/** @internal */
	private _abortController: AbortController | null = null;
	/** @internal */
	private _track: MediaStreamAudioTrack;
	/** @internal */
	private _audioContext: AudioContext | null = null;
	/** @internal */
	// eslint-disable-next-line @typescript-eslint/no-deprecated
	private _scriptProcessorNode: ScriptProcessorNode | null = null; // Deprecated but goated
	/** @internal */
	private _promiseWithResolvers = promiseWithResolvers();
	/** @internal */
	private _errorPromiseAccessed = false;
	/** @internal */
	private _paused = false;

	/** A promise that rejects upon any error within this source. This promise never resolves. */
	get errorPromise() {
		this._errorPromiseAccessed = true;
		return this._promiseWithResolvers.promise;
	}

	/** Whether this source is currently paused as a result of calling `.pause()`. */
	get paused() {
		return this._paused;
	}

	/**
	 * Creates a new {@link MediaStreamAudioTrackSource} from a `MediaStreamAudioTrack`, which will pull audio samples
	 * from the stream in real time and encode them according to {@link AudioEncodingConfig}.
	 */
	constructor(
		track: MediaStreamAudioTrack,
		encodingConfig: AudioEncodingConfig,
		options: MediaStreamAudioTrackSourceOptions = {},
	) {
		if (!(track instanceof MediaStreamTrack) || track.kind !== 'audio') {
			throw new TypeError('track must be an audio MediaStreamTrack.');
		}
		validateAudioEncodingConfig(encodingConfig);
		if (typeof options !== 'object' || !options) {
			throw new TypeError('options must be an object.');
		}
		if (
			options.timestampBase !== undefined
			&& options.timestampBase !== 'synced-zero'
			&& options.timestampBase !== 'zero'
			&& options.timestampBase !== 'unix'
		) {
			throw new TypeError(
				'options.timestampBase, when provided, must be one of \'synced-zero\', \'zero\', or \'unix\'.',
			);
		}

		super(encodingConfig.codec);
		this._options = options;
		this._encoder = new AudioEncoderWrapper(this, encodingConfig);
		this._track = track;
	}

	/** @internal */
	override async _start() {
		if (!this._errorPromiseAccessed) {
			console.warn(
				'Make sure not to ignore the `errorPromise` field on MediaStreamAudioTrackSource, so that any internal'
				+ ' errors get bubbled up properly.',
			);
		}

		this._abortController = new AbortController();

		let firstAudioDataTimestamp: number | null = null;
		let errored = false;
		let lastSampleTimestamp: number | null = null;
		let timestampOffset = 0;

		const onAudioSample = (audioSample: AudioSample) => {
			if (errored) {
				audioSample.close();
				return;
			}

			const currentTimestamp = audioSample.timestamp;

			if (this._paused) {
				const dataSeen = firstAudioDataTimestamp !== null;
				if (dataSeen) {
					if (lastSampleTimestamp !== null && this._options.timestampBase !== 'unix') {
						// In addition to dropping this sample, let's also keep track of the time we have lost due to
						// the pause. Doing it like this instead of simply keeping track of the paused time is better
						// since it retains the sample rate of the underlying source.
						const timeDelta = currentTimestamp - lastSampleTimestamp;
						timestampOffset -= timeDelta;
					}
					lastSampleTimestamp = currentTimestamp;
				}

				audioSample.close();
				return;
			}

			if (firstAudioDataTimestamp === null) {
				firstAudioDataTimestamp = audioSample.timestamp;

				let target: number;
				const timestampBase = this._options.timestampBase ?? 'synced-zero';
				if (timestampBase === 'unix') {
					target = Date.now() / 1000;
				} else if (timestampBase === 'zero') {
					target = 0;
				} else {
					const output = this._connectedTrack!.output;
					if (output._firstMediaStreamTimestamp === null) {
						output._firstMediaStreamTimestamp = performance.now() / 1000;
						target = 0;
					} else {
						target = performance.now() / 1000 - output._firstMediaStreamTimestamp;
					}
				}

				timestampOffset = target - firstAudioDataTimestamp;
			}

			lastSampleTimestamp = currentTimestamp;

			if (this._encoder.getQueueSize() >= 8) {
				// Drop data if the encoder is overloaded
				audioSample.close();
				return;
			}

			audioSample.setTimestamp(currentTimestamp + timestampOffset);

			void this._encoder.add(audioSample, true)
				.catch((error) => {
					errored = true;

					this._abortController?.abort();
					this._promiseWithResolvers.reject(error);
					void this._audioContext?.suspend();
				});
		};

		if (typeof MediaStreamTrackProcessor !== 'undefined') {
			// Great, MediaStreamTrackProcessor is supported, this is the preferred way of doing things
			const processor = new MediaStreamTrackProcessor({ track: this._track });
			const consumer = new WritableStream<AudioData>({
				write: audioData => onAudioSample(new AudioSample(audioData)),
			});

			processor.readable.pipeTo(consumer, {
				signal: this._abortController.signal,
			}).catch((error) => {
				// Handle AbortError silently
				if (error instanceof DOMException && error.name === 'AbortError') return;

				this._promiseWithResolvers.reject(error);
			});
		} else {
			// Let's fall back to an AudioContext approach

			// eslint-disable-next-line @typescript-eslint/no-explicit-any, @typescript-eslint/no-unsafe-member-access
			const AudioContext = window.AudioContext || (window as any).webkitAudioContext;

			this._audioContext = new AudioContext({ sampleRate: this._track.getSettings().sampleRate });
			const sourceNode = this._audioContext.createMediaStreamSource(new MediaStream([this._track]));
			// eslint-disable-next-line @typescript-eslint/no-deprecated
			this._scriptProcessorNode = this._audioContext.createScriptProcessor(4096);

			if (this._audioContext.state === 'suspended') {
				await this._audioContext.resume();
			}

			sourceNode.connect(this._scriptProcessorNode);
			this._scriptProcessorNode.connect(this._audioContext.destination);

			let totalDuration = 0;

			// eslint-disable-next-line @typescript-eslint/no-deprecated
			this._scriptProcessorNode.onaudioprocess = (event) => {
				// eslint-disable-next-line @typescript-eslint/no-deprecated
				const iterator = AudioSample._fromAudioBuffer(event.inputBuffer, totalDuration);
				// eslint-disable-next-line @typescript-eslint/no-deprecated
				totalDuration += event.inputBuffer.duration;

				for (const audioSample of iterator) {
					onAudioSample(audioSample);
				}
			};
		}
	}

	/**
	 * Pauses the capture of audio data - any audio data emitted by the underlying media stream will be ignored
	 * while paused. This does *not* close the underlying `MediaStreamAudioTrack`, it just ignores its output.
	 */
	pause() {
		this._paused = true;
	}

	/** Resumes the capture of audio data after being paused. */
	resume() {
		this._paused = false;
	}

	/** @internal */
	override async _flushAndClose(forceClose: boolean) {
		if (this._abortController) {
			this._abortController.abort();
			this._abortController = null;
		}

		if (this._audioContext) {
			assert(this._scriptProcessorNode);

			this._scriptProcessorNode.disconnect();
			await this._audioContext.suspend();
		}

		await this._encoder.flushAndClose(forceClose);
	}
}

// === MEDIA STREAM TRACK PROCESSOR WORKER ===

type MediaStreamTrackProcessorWorkerMessage = {
	type: 'support';
	supported: boolean;
} | {
	type: 'videoFrame';
	trackId: number;
	videoFrame: VideoFrame;
} | {
	type: 'trackStopped';
	trackId: number;
} | {
	type: 'error';
	trackId: number;
	error: Error;
};

type MediaStreamTrackProcessorControllerMessage = {
	type: 'videoTrack';
	trackId: number;
	track: MediaStreamVideoTrack;
} | {
	type: 'stopTrack';
	trackId: number;
};

const mediaStreamTrackProcessorWorkerCode = () => {
	const sendMessage = (message: MediaStreamTrackProcessorWorkerMessage, transfer?: Transferable[]) => {
		if (transfer) {
			self.postMessage(message, { transfer });
		} else {
			self.postMessage(message);
		}
	};

	// Immediately send a message to the main thread, letting them know of the support
	sendMessage({
		type: 'support',
		supported: typeof MediaStreamTrackProcessor !== 'undefined',
	});

	const abortControllers = new Map<number, AbortController>();
	const activeTracks = new Map<number, MediaStreamVideoTrack>();

	self.addEventListener('message', (event) => {
		const message = event.data as MediaStreamTrackProcessorControllerMessage;

		switch (message.type) {
			case 'videoTrack': {
				activeTracks.set(message.trackId, message.track);

				const processor = new MediaStreamTrackProcessor({ track: message.track });
				const consumer = new WritableStream<VideoFrame>({
					write: (videoFrame) => {
						if (!activeTracks.has(message.trackId)) {
							videoFrame.close();
							return;
						}

						// Send it to the main thread
						sendMessage({
							type: 'videoFrame',
							trackId: message.trackId,
							videoFrame,
						}, [videoFrame]);
					},
				});

				const abortController = new AbortController();
				abortControllers.set(message.trackId, abortController);

				processor.readable.pipeTo(consumer, {
					signal: abortController.signal,
				}).catch((error: Error) => {
					// Handle AbortError silently
					if (error instanceof DOMException && error.name === 'AbortError') return;

					sendMessage({
						type: 'error',
						trackId: message.trackId,
						error,
					});
				});
			}; break;

			case 'stopTrack': {
				const abortController = abortControllers.get(message.trackId);
				if (abortController) {
					abortController.abort();
					abortControllers.delete(message.trackId);
				}

				const track = activeTracks.get(message.trackId);
				track?.stop();
				activeTracks.delete(message.trackId);

				sendMessage({
					type: 'trackStopped',
					trackId: message.trackId,
				});
			}; break;

			default: assertNever(message);
		}
	});
};

let nextMediaStreamTrackProcessorWorkerId = 0;
let mediaStreamTrackProcessorWorker: Worker | null = null;

const initMediaStreamTrackProcessorWorker = () => {
	const blob = new Blob(
		[`(${mediaStreamTrackProcessorWorkerCode.toString()})()`],
		{ type: 'application/javascript' },
	);
	const url = URL.createObjectURL(blob);

	mediaStreamTrackProcessorWorker = new Worker(url);
};

let mediaStreamTrackProcessorIsSupportedInWorkerCache: boolean | null = null;
const mediaStreamTrackProcessorIsSupportedInWorker = async () => {
	if (mediaStreamTrackProcessorIsSupportedInWorkerCache !== null) {
		return mediaStreamTrackProcessorIsSupportedInWorkerCache;
	}

	if (!mediaStreamTrackProcessorWorker) {
		initMediaStreamTrackProcessorWorker();
	}

	return new Promise<boolean>((resolve) => {
		assert(mediaStreamTrackProcessorWorker);

		const listener = (event: MessageEvent) => {
			const message = event.data as MediaStreamTrackProcessorWorkerMessage;

			if (message.type === 'support') {
				mediaStreamTrackProcessorIsSupportedInWorkerCache = message.supported;
				mediaStreamTrackProcessorWorker!.removeEventListener('message', listener);

				resolve(message.supported);
			}
		};

		mediaStreamTrackProcessorWorker.addEventListener('message', listener);
	});
};

const sendMessageToMediaStreamTrackProcessorWorker = (
	message: MediaStreamTrackProcessorControllerMessage,
	transfer?: Transferable[],
) => {
	assert(mediaStreamTrackProcessorWorker);

	if (transfer) {
		mediaStreamTrackProcessorWorker.postMessage(message, transfer);
	} else {
		mediaStreamTrackProcessorWorker.postMessage(message);
	}
};

/**
 * Base class for subtitle sources - sources for subtitle tracks.
 * @group Media sources
 * @public
 */
export abstract class SubtitleSource extends MediaSource {
	/** @internal */
	override _connectedTrack: OutputSubtitleTrack | null = null;
	/** @internal */
	override readonly _codec: SubtitleCodec;

	/** Internal constructor. */
	constructor(codec: SubtitleCodec) {
		super();

		if (!SUBTITLE_CODECS.includes(codec)) {
			throw new TypeError(`Invalid subtitle codec '${codec}'. Must be one of: ${SUBTITLE_CODECS.join(', ')}.`);
		}

		this._codec = codec;
	}
}

/**
 * This source can be used to add subtitles from a subtitle text file.
 * @group Media sources
 * @public
 */
export class TextSubtitleSource extends SubtitleSource {
	/** @internal */
	private _parser: SubtitleParser;
	/** @internal */
	private _error: Error | null = null;
	/** @internal */
	private _lastMuxerPromise: Promise<void> = Promise.resolve();

	/** Creates a new {@link TextSubtitleSource} where added text chunks are in the specified `codec`. */
	constructor(codec: SubtitleCodec) {
		super(codec);

		this._parser = new SubtitleParser({
			codec,
			output: (cue, metadata) => {
				this._lastMuxerPromise
					= this._connectedTrack!.output._muxer.addSubtitleCue(this._connectedTrack!, cue, metadata)
						.catch((error) => {
							this._error ??= error;
						});
			},
		});
	}

	/**
	 * Parses the subtitle text according to the specified codec and adds it to the output track. You don't have to
	 * add the entire subtitle file at once here; you can provide it in chunks.
	 *
	 * @returns A Promise that resolves once the output is ready to receive more samples. You should await this Promise
	 * to respect writer and encoder backpressure.
	 */
	add(text: string) {
		if (typeof text !== 'string') {
			throw new TypeError('text must be a string.');
		}

		this._checkForError();

		this._ensureValidAdd();
		this._parser.parse(text);

		return this._lastMuxerPromise; // Allow the writer to apply backpressure
	}

	/** @internal */
	_checkForError() {
		if (this._error) {
			throw this._error;
		}
	}

	/** @internal */
	override async _flushAndClose(forceClose: boolean) {
		if (!forceClose) {
			this._checkForError();
		}
	}
}