[Bug 22148] Request that we reconsider adding jitter to video quality metrics

https://www.w3.org/Bugs/Public/show_bug.cgi?id=22148

Jerry Smith <jdsmith@microsoft.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|FIXED                       |---

--- Comment #3 from Jerry Smith <jdsmith@microsoft.com> ---
VideoPlaybackQuality playbackJitter was recently incorporated as a video
quality metric.  I believe it was still being discussed with others in the
working group, and that unresolved issues were raised about it on the last MSE
call.  We believe a revision may be needed to accommodate feedback from other
members.

This feedback agreed that jitter would be a useful measure of video rendering
stress, but wasn't ideal because it is an instantaneous measurement that does
not reflect AV sync issues.  Persistent video async might show up as a jitter
spike, but then show no more indication of a problem on the current metric. 
This makes it difficult for an app to detect accumulated latency that could
eventually lead to dropped frames.  A preferred measure would represent the
accumulated total frame delays, so that this persistent latency condition would
be more directly detectable.

In response to this feedback, we are proposing VideoPlaybackQuality
totalFrameDelay as an improved jitter metric, one that reflects both
instantaneous jitter and accumulated latency.  It would continue to accumulate
total delays for the duration of a media session.  The app would be responsible
for keeping a record of its value when the video representation is shifted, so
that total delays for the currently rendering content quality could be
calculated.  We believe this revised measure addresses the feedback we've
received on the previous metric.

interface VideoPlaybackQuality {
    readonly    attribute DOMHighResTimeStamp creationTime;
    readonly    attribute unsigned long       totalVideoFrames;
    readonly    attribute unsigned long       droppedVideoFrames;
    readonly    attribute unsigned long       corruptedVideoFrames;
    readonly    attribute double       totalFrameDelay;  // =====> to replace
PlaybackJitter
};

DEFINITION - 

Given:
                Li represents the lateness of the frame i.  The value is
positive if the frame is late.  The value is set to “0” if the frame is
(available from decoder) ahead of rendering time.

Then:
totalFrameDelay = sum( Li )

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Received on Sunday, 9 June 2013 14:18:26 UTC