Bug 220103 – [GStreamer] More robust video size handling

• Component: WebKitGTK
• Status: RESOLVED FIXED

[Alicia Boya García]

This patch improves the handling of how video size is detected and
reported to WebKit, fixing several issues:

a) The value returned by calling MediaPlayerPrivateGStreamer
::naturalSize() should not change during a given main thread tick,
since this can potentially be read several times from the rendering
code. This caused the elusive racy crash on `ASSERTION FAILED:
!intrinsicSizeChanged || !view().frameView().layoutContext().isInRenderTreeLayout()`
that has been appearing randomly in many layout tests for a very long time.

b) Video rotation used to be handled via bus messages, but this is
also racy, since the handling of bus messages in the main thread is
run on a different priority than other callbacks. This caused a flaky
failure on media/video-orientation.html.

c) In MSE, appending a second initialization segment with a different
video size triggered a video resize on append, before any frames with
the new size has been played.

This patch fixes these three issues: Only the first initialization
segment will trigger a video resize (this is done so we have a video
size on HAVE_METADATA, as the MSE spec expects), but otherwise video
size is emitted on caps changes on the sink. In the case of regular
playback this is delayed until the first frame arrives so that we have
a guarantee that any rotation tag events have traversed the pipeline
(the data flow through a GStreamer pipeline is done in this order:
CAPS event, optional TAG events and then buffers). Video size changes
are done by posting a task to the main thread, which ensures the value
doesn't change during a main thread tick.

The patch also relinquishes usage of MainThreadNotifier so that
successions of quick video size changes (e.g. in a test case) still
trigger the expected events instead of being potentially coalesced.

Since this patch for the most part fixes race conditions that are not
covered in TestExpectations, it doesn't introduce changes in
TestExpectations.

Note: This patch is not enough to fix imported/w3c/web-platform-tests/media-source/mediasource-config-change-*-framesize tests.
That requires further non-trivial fixes regarding how MSE flushes are
handled.

Note: This patch does not fix framesize WebRTC tests. These seem to be
a consequence of notifying the user too early of the frame size and/or
ready state, before any frame is readable, which is a problem
unrelated to these fixes.

[Alicia Boya García]

Created attachment 416692 [details]
Patch

[EWS]

Committed r271128: <https://trac.webkit.org/changeset/271128>

All reviewed patches have been landed. Closing bug and clearing flags on attachment 416692 [details].