Bug 162813 – YouTube stalls when seeking beyond buffered range

• Status: RESOLVED
• Resolution: FIXED
• Component: Media

[Jer Noble]

YouTube stalls when seeking beyond buffered range

[Jer Noble]

Created attachment 290403 [details]
Patch

[Build Bot]

Comment on attachment 290403 [details]
Patch

Attachment 290403 [details] did not pass mac-ews (mac):
Output: http://webkit-queues.webkit.org/results/2178590

New failing tests:
media/media-source/media-source-fudge-factor.html
imported/w3c/web-platform-tests/media-source/mediasource-config-change-mp4-v-framerate.html

[Build Bot]

Created attachment 290407 [details]
Archive of layout-test-results from ews101 for mac-yosemite

The attached test failures were seen while running run-webkit-tests on the mac-ews.
Bot: ews101  Port: mac-yosemite  Platform: Mac OS X 10.10.5

[Build Bot]

Comment on attachment 290403 [details]
Patch

Attachment 290403 [details] did not pass mac-wk2-ews (mac-wk2):
Output: http://webkit-queues.webkit.org/results/2178609

New failing tests:
media/media-source/media-source-fudge-factor.html
imported/w3c/web-platform-tests/media-source/mediasource-config-change-mp4-v-framerate.html

[Build Bot]

Created attachment 290408 [details]
Archive of layout-test-results from ews107 for mac-yosemite-wk2

The attached test failures were seen while running run-webkit-tests on the mac-wk2-ews.
Bot: ews107  Port: mac-yosemite-wk2  Platform: Mac OS X 10.10.5

[Build Bot]

Comment on attachment 290403 [details]
Patch

Attachment 290403 [details] did not pass mac-debug-ews (mac):
Output: http://webkit-queues.webkit.org/results/2178598

New failing tests:
media/media-source/media-source-fudge-factor.html

[Build Bot]

Created attachment 290409 [details]
Archive of layout-test-results from ews114 for mac-yosemite

The attached test failures were seen while running run-webkit-tests on the mac-debug-ews.
Bot: ews114  Port: mac-yosemite  Platform: Mac OS X 10.10.5

[Alex Christensen]

Do we have no test infrastructure that serves a video in predictable chunks with predictable wait times between chunks?  We ought to.

[Jer Noble]

Obsoleted my initial patch. I've uncovered the underlying cause of the seek problem. When seeking, we have to feed the decoder a series of non-displaying samples, starting with an I-frame, in order for the sample representing the seek time to be decoded and displayed.  When we seek to the end of a very long GOP [1], we may have to enqueue hundreds of samples. E.g., for a 10-second GOP of 30 FPS video, we could have to enqueue 299 samples in order to decode the 300th.

When this happens, if we try to enqueue all 300 (e.g.) samples at once, AVSampleBufferDisplayLayer will fail silently, and do so in such a way as that the AVSampleBufferRenderSynchronizer will fail (again, silently) to seek correctly when asked.

The solution is to feed the non-displaying samples into the AVSampleBufferDisplayLayer one at a time until the AVSampleBufferDisplayLayer says it's full, just the same way we do for normal (displaying) samples.

[1] https://en.wikipedia.org/wiki/Group_of_pictures

[Jer Noble]

More diagnosis: after we ask the AVSampleBufferRenderSynchronizer to seek to the new time, it will internally set its own time back to what it was previously. It does this because the only displayable video and audio frames have presentation times back at the original currentTime.

The solution is to make sure to flush both audio renderers and display layers before seeking. I've been trying for the last few days to make a reproducible test case, but I've failed to come up with one which exhibits the issue. I'll file a separate bug to improve testability in this area. :(

[Jer Noble]

Created attachment 291993 [details]
Patch

[Jer Noble]

Created attachment 292223 [details]
Patch

[WebKit Commit Bot]

Comment on attachment 292223 [details]
Patch

Clearing flags on attachment: 292223

Committed r207694: <http://trac.webkit.org/changeset/207694>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.

[Jon Lee]

*** Bug 160569 has been marked as a duplicate of this bug. ***