[Bug 754230] qtdemux: support sparse time ranges in qtdemux without needing a seek for MSE

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=754230

--- Comment #18 from Enrique Ocaña González <eocanha at igalia.com> ---
Unfortunatelly, the MSE and GStreamer layers don't know when a discontinuity
can happen. The JavaScript in the web page knows (in theory), but that's
completely out of our control.

The use case works like this: JavaScript calls SourceBuffer.append() and
provides raw binary data without any indication of what time it belongs to.
Then, it's job of the "parser"[1] to figure out what timestamps and actual
Samples (roughly equivalent to GstBuffers) are generated by that data. Chromium
ChunkDemuxer[2] & MP4 parser[3] and Apple AVStreamDataParser[4] are able to
"blindly" generate the proper timestamps with the raw data provided in appends,
without any context.


[1] https://w3c.github.io/media-source/#sourcebuffer-segment-parser-loop
[2]
https://chromium.googlesource.com/chromium/src/media/+/master/filters/chunk_demuxer.cc
[3]
https://chromium.googlesource.com/chromium/src/media/+/master/formats/mp4/mp4_stream_parser.cc
[4]
https://github.com/WebKit/webkit/blob/master/Source/WebCore/platform/graphics/avfoundation/objc/SourceBufferPrivateAVFObjC.mm#L775

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