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

[Sebastian Dröge]

On Thu, 2016-11-10 at 02:28 -0800, dawnpaul wrote:
> We are doing a gstreamer application which requires AV sync of less than +/-
> 3 ms between audio and video. We use jetson TX1, gstreamer 1.8.0 and
> L4T24.2. Should support 23.976 FPS. We use Sync meter to measure the
> difference between an audio beep and a flash. The observations are at UHD
> 23.976 the sync meter reading is around +1 ms and remain constant sometimes.
> For other session the offset is observed to be around 43 ms which is
> equivalent to one video frame. We tried to print the audio and video
> timestamp using gst_pad_add_probe() and compare. But could not figure out
> the issue.Could we achieve this avsync tolerance with gstreamer. Is there
> another method to debug the issue.

Getting such accurate synchronization between audio and video requires
all parts of the pipeline to work correctly, and to correctly report
their latency (in case of a live pipeline).

Especially also the video sink (and the API used by it) needs to be
able to correctly schedule frames (otherwise you get +/- 1 frame),
which is not easily possible with most APIs. Which sink do you use?

For audio, the driver needs to correctly and accurately report its
latency. Depending on the driver, those values reported can be rather
random.

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