Playlist Loader

Purpose

The PlaylistLoader (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.

Basic Responsibilities

To request an m3u8.
To parse a m3u8 into a format videojs-http-streaming can understand.
To allow selection of a specific media stream.
To refresh a live m3u8 for changes.

Design

States

HAVE_NOTHING the state before the m3u8 is received and parsed.
HAVE_MAIN_MANIFEST the state before a media manifest is parsed and setup but after the main manifest has been parsed and setup.
HAVE_METADATA the state after a media stream is setup.
SWITCHING_MEDIA the intermediary state we go though while changing to a newly selected media playlist
HAVE_CURRENT_METADATA a temporary state after requesting a refresh of the live manifest and before receiving the update

API

load() this will either start or kick the loader during playback.
start() this will start the PL and request the m3u8.
media() this will return the currently active media stream or set a new active media stream.

Events

loadedplaylist signals the setup of a main playlist, representing the HLS source as a whole, from the m3u8; or a media playlist, representing a media stream.
loadedmetadata signals initial setup of a media stream.
playlistunchanged signals that no changes have been made to a m3u8.
mediaupdatetimeout signals that a live m3u8 and media stream must be refreshed.
mediachanging signals that the currently active media stream is going to be changed.
mediachange signals that the new media stream has been updated.

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