Clock skewing algorithm

[Tvrtko Ursulin]

Hi Wim, all,

I was just talking with Jan Schmidt on #gstreamer about a curious clock 
skewing observation you might sched some light at.

Essentially I am debugging AV sync issues when streaming video from v4l2src 
and audio from alsasrc. To narrow it down I went on to test purely audio 
pipeline in the form of "alsasrc ! audio/x-raw-int,rate=48000 ! queue min-
threshold-time=2000000000 ! alsasink".

What happens occasionally is that audio gets choppy and then stops completely. 
I have captured logs of one such incident, pulled out some information from 
clock skewing and plotted it with gnuplot for which I am attaching two plots.

On the full plot you can see that after the second large skew spike average 
skew calculation seems to go wrong and starts oscillating between positive and 
negative values. On the zoomed in view you can see that there is no negative 
skew values, while average keeps oscillating. However on the first occurence of 
such large spike it seems to keep the average correct.

Basically I have two question here. First is whether wrong average skew is 
expected to have negative effects on audio, including stopping completely, and 
then secondly whether it looks like a bug in average skew calculation which 
should be investigated deeper?

Regards,

Tvrtko
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