Maximum AV sync possible with gstreamer 1.8.0 in L4T 24.2 at 23.976 FPS

[Sebastian Dröge]

On Sun, 2016-11-13 at 22:14 -0800, dawnpaul wrote:
> We are playing media from MP4 file. We used nveglglessink as video sink. We
> also tried fpsdisplaysink. In both case the AV sync issue has similar
> results. We used alsasink as audio sink and avdec_aac as audio decoder. We
> probed the video and audio timestamps at each stage of pipeline and observed
> that time difference between first audio and video  timestamp after the
> video decoder has delay approximately equal to one frame. The difference is
> in time at which the print is coming in gst-debug. The issue is more
> frequent in UHD than FHD. So could we confirm that issue is with video
> decoder since it is the most intensive task in the pipeline. Could we try to
> query the decoder latency dynamically and adjust the pipeline latency in a
> non live source. What could be the best method to figure out where is the
> issue. Issue appears only in some sessions. Approximately once in 5
> sessions.

In non-live pipelines the latency does not matter as everything pre-
rolls to the sink first before output actually starts.

My best guess from your description is that the problem is inside the
video sink, and frames are being sent to OpenGL exactly at the time
when they should be displayed but that often causes them to only be
displayed on the next VSYNC (i.e. one frame too late then).

Solving this requires feedback from the driver to know when VSYNC is
happening and then based on that schedule the frames accordingly.

-- 
Sebastian Dröge, Centricular Ltd · http://www.centricular.com
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