[mythtv-users] Sound Synchronization Problem In Live TV

Mark Goldberg marklgoldberg at gmail.com
Fri Dec 29 18:19:13 UTC 2006

I've got an unusual sound synchronization problem that seems to occur
after watching live tv from an ATSC tuner after some time. After maybe
a 1/2 hour or so, the sound is slightly out of syncronization and it
gets worse with time. Using the left arrow key to rewind a few seconds
usually fixes it. Stopping live TV and starting again always fixes it
until it drifts out again. It does not happen on recorded shows, and
it does not seem to happen if the show that is being watched is also
being recorded, but I can't be sure of that.

Relevent info:

Mythtv mythtv-0.20-148 from Atrpms for 64 bit fc6.
Asus M2NPV-VM motherboard with Athlon 64 X2 4200, 2 GB RAM and 320 GB
SATA drive.
(Onboard Nvidia 6150 video, Svideo out to SD TV)
(Onboard AD1986 audio)


This is a result of updating alsa from Atrpms but needing to remove
most of it due to incompatible kernel module for saa7134-alsa.

2 Kworld ATSC-110 tuners.

In kernel boot parameters pci=nomsi, needed originally for sound to
work, may not be needed for 2868 kernel.

In modprobe.conf, options snd-hda-intel index=0 position_fix=1
model=3stack, needed for sound to work.

Nvidia drivers from NVIDIA-Linux-x86_64-1.0-9746-pkg2.run

In xorg.conf
glx is loaded
UseEvents is enabled to get rid of high Xorg cpu
TripleBuffer is not enabled, as it causes lots of stuff not to work

in nvidia-settings
XV Sync and XV Blitter Sync enabled
OpenGL Vblank enabled and Allow Flipping enabled

Without OpenGL, stuttering resulted, and without XVSync, tearing resulted.

In mythtv playback setup
standard mpeg decoder, bob deinterlacing, OpenGL sync, 28900 ( I
think)  HD ringbuffer
/dev/dsp for audio

All this was determined by trial and error to give the best
performance with no tearing and about 80% on one cpu from mythfrontend
while watching live TV, with an occasional prebuffering pause when the
backend does something like commercial flagging or expiring and old
recording with occasional other prebuffering issues. I also get

XvMCTex: Init failed
XVideo Adaptor Name: 'NV17 Video Texture'
X Error: BadMatch (invalid parameter attributes) 8
  Major opcode:  142
  Minor opcode:  14
  Resource id:  0x198

but don't know if that is relevent.

Any suggestions as to what may be the problem or what to try to
troubleshoot things?
I've not seen an issue like this recently in the list archives.



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