This adds both av1C and AV1 sequence header OBU parsing, which is used by MediaChangeMonitor to determine whether a new decoder is needed when the codec configuration changes during playback.
AV1 codec strings from MediaCapabilities, HTMLVideoElement.canPlayType and MediaSource.isTypeSupported will be converted to av1C format with a sequence header attached and passed to decoders to initialize them, allowing better detection of codec support in software or hardware to be implemented.
Differential Revision: https://phabricator.services.mozilla.com/D141720
Zaggy1024