| 1 | # Playlist Loader
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| 2 |
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| 3 | ## Purpose
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| 4 |
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| 5 | The [PlaylistLoader][pl] (PL) is responsible for requesting m3u8s, parsing them and keeping track of the media "playlists" associated with the manifest. The [PL] is used with a [SegmentLoader] to load ts or fmp4 fragments from an HLS source.
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| 6 |
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| 7 | ## Basic Responsibilities
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| 8 |
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| 9 | 1. To request an m3u8.
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| 10 | 2. To parse a m3u8 into a format [videojs-http-streaming][vhs] can understand.
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| 11 | 3. To allow selection of a specific media stream.
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| 12 | 4. To refresh a live master m3u8 for changes.
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| 13 |
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| 14 | ## Design
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| 15 |
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| 16 | ### States
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| 17 |
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| 18 | 
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| 19 |
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| 20 | - `HAVE_NOTHING` the state before the m3u8 is received and parsed.
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| 21 | - `HAVE_MASTER` the state before a media manifest is parsed and setup but after the master manifest has been parsed and setup.
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| 22 | - `HAVE_METADATA` the state after a media stream is setup.
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| 23 | - `SWITCHING_MEDIA` the intermediary state we go though while changing to a newly selected media playlist
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| 24 | - `HAVE_CURRENT_METADATA` a temporary state after requesting a refresh of the live manifest and before receiving the update
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| 25 |
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| 26 | ### API
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| 27 |
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| 28 | - `load()` this will either start or kick the loader during playback.
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| 29 | - `start()` this will start the [PL] and request the m3u8.
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| 30 | - `media()` this will return the currently active media stream or set a new active media stream.
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| 31 |
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| 32 | ### Events
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| 33 |
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| 34 | - `loadedplaylist` signals the setup of a master playlist, representing the HLS source as a whole, from the m3u8; or a media playlist, representing a media stream.
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| 35 | - `loadedmetadata` signals initial setup of a media stream.
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| 36 | - `playlistunchanged` signals that no changes have been made to a m3u8.
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| 37 | - `mediaupdatetimeout` signals that a live m3u8 and media stream must be refreshed.
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| 38 | - `mediachanging` signals that the currently active media stream is going to be changed.
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| 39 | - `mediachange` signals that the new media stream has been updated.
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| 40 |
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| 41 | ### Interaction with Other Modules
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| 42 |
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| 43 | 
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| 44 |
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| 45 | [pl]: ../src/playlist-loader.js
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| 46 | [sl]: ../src/segment-loader.js
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| 47 | [vhs]: intro.md
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