[mythtv-users] HELP: What is meaning of "NVP: Video is 16.2157 frames ahead of audio, doubling video frame interval to slow down."

Jeffrey J. Kosowsky mythtv-users at kosowsky.org
Fri Dec 5 20:44:08 UTC 2008

Mitch Gore wrote at about 14:19:45 -0600 on Friday, December 5, 2008:
 > On Fri, Dec 5, 2008 at 2:17 PM, Jeffrey J. Kosowsky
 > <mythtv-users at kosowsky.org> wrote:
 > > I believe this is the cause of the problems I am experiencing with
 > > slow video, and halting sound.
 > >
 > > Specifically:
 > > - HD video is good quality & smooth but slow.
 > > - Sound is normal quality and speed/frequency, but stops every few
 > >  seconds (though no sound is missing).
 > > It seems like sound is stopping every couple of seconds to wait for
 > > the slow video to catch up.
 > >
 > > This would be consistent with the error message that I get with each
 > > audio pause:
 > >          WriteAudio: buffer underrun
 > >
 > > However, this symptom seems like the OPPOSITE of the message that I
 > > get when I turn on "-v playback":
 > >        Video is N.nnnn frames ahead of audio, doubling video frame
 > >        interval to slow down.
 > >
 > > where N ranges from about 8 to 16 frames -- which would be consistent
 > > with approximately the length of the audio pauses.
 > >
 > > So my questions are:
 > > - Is this a video problem or an audio problem?
 > > - Is this a cpu or graphics card speed problem?
 > > - What do I need to do to troubleshoot & fix?
 > >
 > > Note: I have a 2.8GHz P4 (old) with a new GeForce 6200 card.
 > > Mythfrontend uses about 40-45% of CPU.
 > > X uses about 4-6% (using XvMC)
 > > Mythbackend uses about 15%
 > > Pulseaudio uses about 8%.
 > >
 > > _______________________________________________
 > > mythtv-users mailing list
 > > mythtv-users at mythtv.org
 > > http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
 > >
 > Did you try enabling extra audio buffering in tv playback general settings?

Yes - it didn't help at all.

And I don't think it should since this is not a 1-time buffering
problem - but rather seems to be a continual one whereby the sound is
waiting for the "slow" video to catch up.

i.e. observationally, it seems like the sound plays at normal speed
until it gets too far AHEAD (say 1/3 - 1/2 second) of the slower video
then it pauses to wait for the video to "catch up". But then it
immediately continues to get ahead of the video again and the cycle

So I don't think any amount of buffering will help.
I need to understand why the video is playing "slow" and what I can do
to speed it up (I tried with/without XvMC and with/without

I know my CPU is old but it is not getting 100% usage -- and in fact,
on my old Nvidia 4600 card the total CPU usage was higher even if with
analog TV.

Also, I still don't understand the error message: 
	  Video is 16.2157 frames ahead of audio, doubling video frame
	  interval to slow down.
Since it seems like the video is BEHIND -- hence the slow-mo video and
the pause in audio while waiting for video to catch up.

Interestingly, in mplayer, the sound and video play smoothly (under
XvMC) though the audio gets gradually further ahead of the video. This
despite the fact that mplayer is only using 35-40% of CPU, X using
10-15% and pulseaudio 5-8% -- so total CPU usage is about 60%.

It seems like the problem is worse now with the new 6200 card than
with my old 4600 card (without XvMC) when total CPU usage was closer
to 100%.

I tried both the 96.43.07 and the 173.14.12 atrpms drivers.

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