The first second of a VOD asset was not played on Shaka player

[hoimingw]

We tested a VOD asset on Shaka player, and found that the first second of video was not played. i.e. The playback was started from the 2nd second. After investigation, it was caused by the incorrect value of video.currentTime assigned by Shaka player.

MPD information:
<AdaptationSet mimeType="video/mp4" startWithSAP="1" segmentAlignment="true"> <SegmentTemplate timescale="10000000" presentationTimeOffset="0" media="$RepresentationID$/Segment-$Time$.m4v" initialization="$RepresentationID$/init.m4i"> <SegmentTimeline> <S t="9927777" d="20000000" r="256"/> <S t="5149927777" d="6800000"/> </SegmentTimeline> </SegmentTemplate> <Representation width="384" height="216" frameRate="25" codecs="avc1.4d400d" scanType="progressive" id="stream_0" bandwidth="280000"/> </AdaptationSet> <AdaptationSet mimeType="audio/mp4" startWithSAP="1" lang="rus" segmentAlignment="true"> <SegmentTemplate timescale="10000000" presentationTimeOffset="0" media="$RepresentationID$/Segment-$Time$.m4a" initialization="$RepresentationID$/init.m4i"> <SegmentTimeline> <S t="0" d="30720000"/> <S t="30720000" d="20480000"/> <S t="51200000" d="19200000"/> <S t="70400000" d="20480000"/>...

Shaka player set the currentTime of the video element to 9927777, which was the first PTS of the video stream, while the "Base media decode time" for the first video segment was 9527777. As a result, the timestampCorrection obtained (shaka.media.SourceBufferManager.prototype.fetch) for video and audio streams were -0.0400007 and 0, respectively.

However, Shaka player calculated the global timestampCorrection by choosing the maximum timestampCorrection among all streams, and then use the global timestampCorrection (value = 0) to call beginPlayback_, and thus the playback was started from 9927777 instead of 9527777 which had skipped the first IDR frame, and then resulted in the first second of video was not played.

After manually setting the global timestampCorrection to -0.0400007, all video were played successfully.

[joeyparrish]

@hoimingw, can you please give us some more details? What version of Shaka are you using? Are you using shaka-player-demo.appspot.com or running from source?

[tdrews]

We have completely done away with the timestamp correction mechanism in Shaka v2. What type of behavior do you see from the master branch?

[hoimingw]

@joeyparrish , sorry for my late response. I was testing the issue with self-hosting Shaka player v1.6.5.

[hoimingw]

@tdrews , Thanks for your information, we will test it on v2.

[tdrews]

Hi, any luck with Shaka v2?

[hoimingw]

The issue is blocked by #348, the fix should have been committed to master but not officially released yet. We will test with the master branch though.
Thanks,

[hoimingw]

Test with Shaka player 2.0.0-beta2 (2016-05-04), the problem still exist. (The first second of video is missing).

[joeyparrish]

Can you provide us with a manifest URL to reproduce the issue?

[hoimingw]

Hi joeyparrish,

I don't want to post our test content to public, may I have your email address so that I can share the content with you?

Thanks,

[joeyparrish]

My email address can be found in CONTRIBUTORS. Please send to Joey Parrish and Timothy Drews.

[hoimingw]

Hi Joey,
The link to the test asset has been sent to you and Timothy.
Thanks,

[tdrews]

@kqyang has determined that this is a bug in Chrome itself:
see https://bugs.chromium.org/p/chromium/issues/detail?id=398130

[hoimingw]

Hi Tim,
Great thanks for your help!
Hoi Ming