[mythtv-users] Playback problem -- random short pauses

Kenneth Emerson kenneth.emerson at gmail.com
Thu Mar 24 15:03:28 UTC 2011

I have been following several of the threads on this list (and the commit
list) that have talked about "stuttering" during playback.  I don't believe
that these issues are describing what I am seeing on my system.  My symptoms
seem to have started happening about two months ago but I cannot pinpoint
the time to some specific change in either my FE/BE combination or the
version of mythTV.  I keep both my OS (Ubuntu 10.04 32 bit) and mythTV
(24-fixes currently v0.24-227-gccd73be) up to date.  My version of NVIDIA
driver is 260.19.21.  My system is based on an Intel Q6600 quad core 2.4GHz
cpu.  The video being watched is primarily either 720p or 1080i material.  I
don't believe I have ever seen the problem on 480 material, but that data
set may be too small to matter.

The specific problem I see during playback is a random, short pause with
either missing frames or missing audio; hard to tell which.  The pause is
very short (less than 2 seconds) but long enough to miss 1-3 words of the
dialog.  The video is not damaged since I can back up and replay the same
segment without any interruption.  These pauses are random and occur
anywhere from none in an hour-long show to four or five times in that
period.  It is not related to the scheduler starting/stopping other
recordings as I check my watch every time one occurs.  I do see a slight
stutter, occasionally, when I know there are other recordings
stopping/starting and that is a different and less annoying symptom.  I also
limit the number of simultaneous jobs to two and I hold off commflagging
until after the recordings have finished.  There appears to be nothing of
interest in the frontend log.  I occasionally see "ALSA, Error: WriteAudio:
buffer underrun" messages, but these do not seem to correlate to the pauses.

I am looking for any ideas on how to proceed to troubleshoot this problem.
 The WAF is not plummeting, but I do get the occasional, exasperated
question "Why does it do that?" which, unfortunately, I cannot answer
but desperately want to be able to.

-- Ken E.
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