Thanks for filing this, Sergey.

Note that MSE v1 spec will probably have TrackDefaults marked at-risk, and decision about whether TrackDefaults remains in the spec will be made while the spec is transitioning through W3C's "PR" -> "REC" phases.

I think we should anticipate doing the right thing (keep TrackDefaults in our impl), and hope other implementors catch up with this feature that's been in the spec quite a while now. Worst case, we might eventually need to deprecate the TrackDefaults feature.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/efae0344beeff450bbd5c9d1bff69c3d5d6f7104

commit efae0344beeff450bbd5c9d1bff69c3d5d6f7104
Author: servolk <servolk@chromium.org>
Date: Thu Jun 30 21:12:43 2016

Implement InitSegmentReceived algorithm in blink

This CL begins moving MSE init segment received algorithm implementation
to blink level, so that it could be shared across different
implementations (e.g. between Chrome and Opera). The old init segment
algorithm is in MediaSourceState::OnNewConfigs, and for now it needs to
be kept, since it does other important things that must be done on the
Chromium media pipeline level atm (e.g. creating track buffers and
demuxer streams).

BUG= 620881 

Review-Url: https://codereview.chromium.org/1678523003
Cr-Commit-Position: refs/heads/master@{#403286}

[modify] https://crrev.com/efae0344beeff450bbd5c9d1bff69c3d5d6f7104/media/blink/websourcebuffer_impl.cc
[modify] https://crrev.com/efae0344beeff450bbd5c9d1bff69c3d5d6f7104/third_party/WebKit/LayoutTests/http/tests/media/media-source/mediasource-avtracks.html
[add] https://crrev.com/efae0344beeff450bbd5c9d1bff69c3d5d6f7104/third_party/WebKit/LayoutTests/http/tests/media/media-source/mediasource-initsegmentreceived-alg.html
[modify] https://crrev.com/efae0344beeff450bbd5c9d1bff69c3d5d6f7104/third_party/WebKit/LayoutTests/http/tests/media/resources/media-source/webm/test.webm
[modify] https://crrev.com/efae0344beeff450bbd5c9d1bff69c3d5d6f7104/third_party/WebKit/Source/modules/mediasource/SourceBuffer.cpp
[modify] https://crrev.com/efae0344beeff450bbd5c9d1bff69c3d5d6f7104/third_party/WebKit/Source/modules/mediasource/SourceBuffer.h
[modify] https://crrev.com/efae0344beeff450bbd5c9d1bff69c3d5d6f7104/third_party/WebKit/Source/modules/mediasource/TrackDefault.cpp
[modify] https://crrev.com/efae0344beeff450bbd5c9d1bff69c3d5d6f7104/third_party/WebKit/Source/modules/mediasource/TrackDefault.h
[modify] https://crrev.com/efae0344beeff450bbd5c9d1bff69c3d5d6f7104/third_party/WebKit/public/platform/WebSourceBufferClient.h

Moving this nonessential bug to the next milestone.

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