[mythtv-users] stuttering problem (doubling video frame interval to slow down)

Bryan Murphy bmurphy1976 at gmail.com
Thu Jul 31 06:07:43 UTC 2008


Hey guys, I've trawled the mailing list archive for this problem.  I've
found a few people talking about it, but no definitive fix.
My Problem:

I've got one channel (our local PBS affiliate) that is giving me grief.
 Every video I record off of it plays back as if it's trapped in slow
motion.  The video is slow, the audio is slow and crackly, and the log is
filled with messages such as the following:

2008-07-30 23:34:00.259 NVP: Video is 3.44581 frames ahead of audio,
                        doubling video frame interval to slow down.
2008-07-30 23:34:00.259 Disabled deinterlacing
2008-07-30 23:34:00.309 NVP: Video is 6.10433 frames ahead of audio,
                        doubling video frame interval to slow down.
2008-07-30 23:34:00.359 NVP: Video is 8.05778 frames ahead of audio,
                        doubling video frame interval to slow down.
2008-07-30 23:34:00.408 NVP: Video is 9.48239 frames ahead of audio,

I've tried as many different combinations of settings as I could think of to
no avail.  Every video I record off of this channel exhibits this problem.

* "Audio Output Device: ALSA:default", jittery audio & video.
* "Audio Output Device: /dev/dsp", smooth video, no audio.  The frontend
complains that /dev/dsp is locked by another process, however, when I fuser
/dev/dsp I see nobody using it.
* "Aggressive Sound Card Buffering: unchecked", no impact.
* "Resolution: 1280x768 @ 60Hz".  Changing resolution has no impact.
* "Enable realtime priority threads: checked", no impact.
* "Extra audio buffering: unchecked", no impact.
* "Use video as timebase: unchecked", no impact.
* "Enable OpenGL vertical sync for timing: checked", no impact.
* "Decoder: Standard", no impact.
* "Video Renderer: xv-blit", no impact.
* "OSD Renderer: softblend", no impact.
* "OSD Fade: unchecked", no impact.
* "Primary Deinterlacer: None"
* "Fallback Deinterlacer: None"
* mythfrontend and mythbacked are chmod u+s
* cat /proc/sys/dev/rtc/max-user-freq = 1024
* "xorg.conf:XvmcUsesTextures = 1", no impact.
* "xorg.conf:NVAGP = 2", no impact.
* "xorg.conf:UseEvents = true", no impact.

I'm currently using OpenGL vsync and according to the mythfrontend output it
appears to be working:

2008-07-30 23:33:59.939 OpenGLVideoSync()
2008-07-30 23:33:59.945 OpenGLVideoSync: x,y -> 800, 600
2008-07-30 23:34:00.173 Using OpenGLVideoSync

I also don't use a deinterlacer because I'm assuming the HD content I'm
recording does not need to be deinterlaced.  I may be wrong, however,
changes to the deinterlacer do not fix this problem and often create new
problems of their own.

Finally, some info about my computer:

* Ubuntu + Medibuntu 8.04
* MythTV TRUNK Build (updated this afternoon)
* Nvidia GeForce FX 5200
* Latest NVIDIA driver
* Pentium 4 3.2GHZ 1GB/ram, 500GB HD + 160GB HD
* PcHDTV 5500
* File Systems: XFS

I've uploaded some additional information.  The first url below is a log of
verbose mythfrontend output during playback of a problematic video.  The
second is a more detailed look at my system, including pci, cpu, and memory
information, as well as a 3 second snapshot iostat output during playback
that clearly shows that I/O and CPU are not an issue.

http://pastebin.com/f36f319b3 (mythfrontend log)
http://pastebin.com/f7fcd0b66 (system information)

Can anybody help?  I've run out of ideas and I don't know where to look
next.

Thanks,
Bryan
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