--- summary: "Per-channel audio formats, transcoding, and what Auto-TTS sends" title: "Text-to-speech output and Auto-TTS behavior" read_when: - You need the audio format a channel receives - You are debugging voice-note delivery or transcoding - You want to know when Auto-TTS summarizes or truncates a reply --- ## Output formats TTS voice delivery is channel-capability driven. Channel plugins advertise whether voice-style TTS should ask providers for a native `voice-note` target or keep normal `audio-file` synthesis, and whether the channel transcodes non-native output before sending. One-off speech requests from the agent tool and `/tts` commands use the same channel delivery rules as automatic replies. Telegram also advertises captioned final TTS. With `tts.mode: "final"` and Auto-TTS set to `always` (or eligible `inbound` mode), streamed text is held until synthesis finishes and sent as the voice-note caption. Text beyond Telegram's caption limit follows the voice note as a normal text message. If synthesis or a proven pre-send delivery step fails, OpenClaw sends the visible text instead. When that fallback follows an immediate delivery result, it comes before later replies from the same turn. Channels that buffer sends until the turn settles may send the fallback after their buffered replies. `tagged` mode keeps its normal streaming behavior, and text inside a `[[tts:text]]` block remains audio-only. After synthesis, OpenClaw persists batch TTS output in the media store under `tool-speech-synthesis`. The reply uses that stable media path instead of a provider temporary file, and normal media maintenance prunes expired output. Local CLI providers may still use `{{OutputPath}}` as scratch space before OpenClaw imports the completed bytes. See [Media playback](/nodes/media-playback) for inline-player formats and limits. | Target | Format | | ------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------- | | Feishu / Matrix / Telegram / WhatsApp | Voice-note replies prefer **Opus** (`opus_48000_64` from ElevenLabs, `opus` from OpenAI). 48 kHz / 64 kbps balances clarity and size. | | Other channels | **MP3** (`mp3_44100_128` from ElevenLabs, `mp3` from OpenAI). 44.1 kHz / 128 kbps is the default balance for speech. | | Talk / telephony | Provider-native **PCM** (Inworld 22050 Hz, Google 24 kHz), or `ulaw_8000` from Gradium for telephony. | Per-provider notes: - **Feishu / WhatsApp transcoding:** when a voice-note reply lands as MP3/WebM/WAV/M4A or another likely audio file, the channel plugin transcodes it to 48 kHz Ogg/Opus with `ffmpeg` (`libopus`, 64 kbps) before sending the native voice message. WhatsApp sends the result through the Baileys `audio` payload with `ptt: true` and `audio/ogg; codecs=opus`. On transcode failure: Feishu catches the error and falls back to sending the original file as a plain attachment; WhatsApp has no fallback, so the send itself fails rather than posting an incompatible PTT payload. - **MiniMax:** MP3 (`speech-2.8-hd` model, 32 kHz sample rate) for normal audio attachments; transcoded to 48 kHz Opus with `ffmpeg` for channel-advertised voice-note targets. - **Xiaomi MiMo:** MP3 by default, or WAV when configured; transcoded to 48 kHz Opus with `ffmpeg` for channel-advertised voice-note targets. - **Local CLI:** uses the configured `outputFormat`. Voice-note targets are converted to Ogg/Opus and telephony output is converted to raw 16 kHz mono PCM with `ffmpeg`. - **Google Gemini:** returns raw 24 kHz PCM. OpenClaw wraps it as WAV for audio attachments, transcodes it to 48 kHz Opus for voice-note targets, and returns PCM directly for Talk/telephony. - **Gradium:** WAV for audio attachments, Opus for voice-note targets, and `ulaw_8000` at 8 kHz for telephony. - **Inworld:** MP3 for normal audio attachments, native `OGG_OPUS` for voice-note targets, and raw `PCM` at 22050 Hz for Talk/telephony. - **xAI:** MP3 by default; audio-file synthesis may use `mp3`, `wav`, `pcm`, `mulaw`, or `alaw` for both buffered and streaming output. Voice-note targets use MP3 for streaming and buffered fallback because xAI's `pcm`, `mulaw`, and `alaw` outputs are headerless raw audio. Buffered synthesis uses xAI's batch REST `/v1/tts` endpoint; `textToSpeechStream` uses native `wss://api.x.ai/v1/tts`. This is not the realtime voice contract. Native Opus voice-note format is not supported. - **Microsoft:** uses `microsoft.outputFormat` (default `audio-24khz-48kbitrate-mono-mp3`). - The bundled transport accepts an `outputFormat`, but not all formats are available from the service. - Output format values follow Microsoft Speech output formats (including Ogg/WebM Opus). - Telegram `sendVoice` accepts OGG/MP3/M4A; use OpenAI/ElevenLabs if you need guaranteed Opus voice messages. - If the configured Microsoft output format fails, OpenClaw retries with MP3. - When no explicit voice override is set and the default English voice is used, OpenClaw auto-switches to a Chinese neural voice (`zh-CN-XiaoxiaoNeural`, `zh-CN` locale) if the reply text is CJK-dominant. OpenAI and ElevenLabs choose output formats per channel as listed above. An explicit OpenAI `responseFormat` overrides that selection; a format that is not voice-note compatible may be delivered as an audio file or transcoded by a channel that supports conversion. ## Auto-TTS behavior When `tts.auto` is enabled, OpenClaw: - Keeps terminal slash and plugin command replies text-only, including with `auto: "always"`. Explicit speech requests such as `/tts audio` and `/tts latest` still send audio. Commands that continue into an assistant run keep the normal auto-TTS behavior for the assistant's answer. - Skips TTS if the reply already contains structured media. - Skips very short replies (under 10 chars). - Skips replies dominated by fenced code; inline code and surrounding prose remain eligible for speech. - Summarizes long replies when summaries are enabled, using `summaryModel` (or `agents.defaults.model.primary`). Summary model access uses the replying agent's credentials and ownership. - Attaches the generated audio to the reply. - In `mode: "final"`, sends TTS after streamed text completes. Channels without captioned-final support receive an audio-only supplement; Telegram puts text within its caption limit on the voice note and sends overflow as follow-up text. Generated media goes through the same channel media normalization as normal reply attachments. If the reply exceeds `maxLength`, OpenClaw never skips audio outright: - **Summary on** (default) and a summary model is available: summarizes the text to roughly `maxLength` chars, then synthesizes the summary. - **Summary off**, summarization fails, or no API key is available for the summary model: truncates the text to `maxLength` chars and synthesizes the truncated text. ```text Reply -> TTS enabled? no -> send text yes -> has media / short? yes -> send text no -> length > limit? no -> TTS -> attach audio yes -> summary enabled and available? no -> truncate -> TTS -> attach audio yes -> summarize -> TTS -> attach audio ```