[mythtv-users] A/V Sync problem only on some PBS Hi-def shows

[DaveD]

I've posted this problem a couple of times in the past, so far no 
solutions.  I have bad (unwatchable) A/V sync on some of our 720p HD PBS 
shows.  Some shows (Desert Speaks) always work, some shows (e2) never 
work.  They are all recorded over cable (QAM), some times with a 
PC-HD3000, some times with a Fusion 5 Gold.  Same problem in playback on 
two different systems that have no trouble with any 1080i shows from 
commercial stations.  One user on the list replied that he has identical 
problems.  He also has Comcast in Seattle.  He noticed changing frame 
rates when watching problem shows in Mplayer.  I got an answer from the 
engineer at our PBS station who said all their shows use the same 
compression algorithm.  I have had this problem for some time.  It seems 
to have started in between Myth upgrades, while using a stable version 
(0.20, I think).  No upgrade (0.21 trunk or 0.21 release) has affected 
it.  All shows play fine in Mplayer and Xine.

After my upgrade to 0.21 failed to fix it, I revisited staring at the 
mythfrontend output, looking for differences between when it works and 
when it doesn't.  I have finally found something very significant.  When 
the shows exhibit the problem, there is a third connection established 
to the database.  I have tried several times and every time I watch a 
show that works, there are two connections.  Every time I watch a show 
that doesn't work, there are three database connections.  Then, a few 
lines later, I get repeated
   NVP::AddAudioData():p1: Audio buffer overflow, audio data lost!
Also, it seems to open the codecs twice!  I'm assuming this is related 
to the extra database connection.  I also see different coded ID numbers 
and, according to the station engineer, their compression algorithms are 
always the same and their HD shows are all 720p.

Here are the lines from the output when it works:

2008-04-01 22:50:18.052 TV: Attempting to change from None to 
WatchingPreRecorded
2008-04-01 22:50:18.227 AFD: Opened codec 0x96a7500, id(MPEG2VIDEO) 
type(Video)
2008-04-01 22:50:18.227 AFD: codec AC3 has 6 channels
2008-04-01 22:50:18.228 AFD: Opened codec 0x96b4370, id(AC3) type(Audio)
2008-04-01 22:50:18.230 Opening audio device 'default'. ch 2(2) sr 48000
2008-04-01 22:50:18.230 Opening ALSA audio device 'default'.
2008-04-01 22:50:18.978 VideoOutputXv: XVideo Adaptor Name: 'NV17 Video 
Overlay'
2008-04-01 22:50:19.091 OSD Theme Dimensions W: 640 H: 480
2008-04-01 22:50:20.281 Realtime priority would require SUID as root.
2008-04-01 22:50:20.281 TV: Changing from None to WatchingPreRecorded
2008-04-01 22:50:20.386 Video timing method: USleep with busy wait
2008-04-01 22:50:20.895 AO: dropping back audio_buffer_unused
2008-04-01 22:50:20.980 AO: dropping back audio_buffer_unused
2008-04-01 22:50:21.023 AO: dropping back audio_buffer_unused
2008-04-01 22:50:21.157 AO: dropping back audio_buffer_unused
2008-04-01 22:50:21.302 AO: dropping back audio_buffer_unused
2008-04-01 22:50:21.393 AO: dropping back audio_buffer_unused
2008-04-01 22:50:21.485 AO: dropping back audio_buffer_unused
2008-04-01 22:50:21.611 AO: dropping back audio_buffer_unused
2008-04-01 22:50:21.707 AO: dropping back audio_buffer_unused
2008-04-01 22:50:21.835 AO: dropping back audio_buffer_unused
2008-04-01 22:50:21.993 AO: dropping back audio_buffer_unused
2008-04-01 22:50:22.154 AO: dropping back audio_buffer_unused
2008-04-01 22:50:22.313 AO: dropping back audio_buffer_unused
2008-04-01 22:50:22.442 AO: dropping back audio_buffer_unused
2008-04-01 22:50:22.569 AO: dropping back audio_buffer_unused
2008-04-01 22:50:22.698 AO: dropping back audio_buffer_unused
2008-04-01 22:51:52.714 TV: Attempting to change from 
WatchingPreRecorded to None
2008-04-01 22:51:52.788 TV: Changing from WatchingPreRecorded to None

Here are the lines from the same section of the output when it doesn't work:

2008-04-01 22:48:19.499 TV: Attempting to change from None to 
WatchingPreRecorded
2008-04-01 22:48:19.501 New DB connection, total: 3
2008-04-01 22:48:19.502 Connected to database 'mythconverg' at host: 
192.168.0.5
2008-04-01 22:48:19.593 AFD: Opened codec 0xcf3c80, id(MPEG2VIDEO) 
type(Video)
2008-04-01 22:48:19.593 AFD: codec AC3 has 6 channels
2008-04-01 22:48:19.594 AFD: Opened codec 0x41f8d00, id(AC3) type(Audio)
2008-04-01 22:48:19.850 AFD: Opened codec 0x966df30, id(MPEG2VIDEO) 
type(Video)
2008-04-01 22:48:19.850 AFD: codec AC3 has 6 channels
2008-04-01 22:48:19.851 AFD: Opened codec 0x9689ae0, id(AC3) type(Audio)
2008-04-01 22:48:19.854 Opening audio device 'default'. ch 2(2) sr 48000
2008-04-01 22:48:19.854 Opening ALSA audio device 'default'.
2008-04-01 22:48:19.961 VideoOutputXv: XVideo Adaptor Name: 'NV17 Video 
Overlay'
2008-04-01 22:48:20.105 OSD Theme Dimensions W: 640 H: 480
2008-04-01 22:48:21.356 Realtime priority would require SUID as root.
2008-04-01 22:48:21.356 TV: Changing from None to WatchingPreRecorded
2008-04-01 22:48:21.459 Video timing method: USleep with busy wait
2008-04-01 22:48:22.487 AO: dropping back audio_buffer_unused
2008-04-01 22:48:22.667 AO: dropping back audio_buffer_unused
2008-04-01 22:48:22.711 AO: dropping back audio_buffer_unused
2008-04-01 22:48:22.811 AO: dropping back audio_buffer_unused
2008-04-01 22:48:22.926 AO: dropping back audio_buffer_unused
2008-04-01 22:48:23.144 AO: dropping back audio_buffer_unused
2008-04-01 22:48:23.236 AO: dropping back audio_buffer_unused
2008-04-01 22:48:23.363 AO: dropping back audio_buffer_unused
2008-04-01 22:48:23.521 AO: dropping back audio_buffer_unused
2008-04-01 22:48:23.745 AO: dropping back audio_buffer_unused
2008-04-01 22:48:23.874 AO: dropping back audio_buffer_unused
2008-04-01 22:48:23.937 AO: dropping back audio_buffer_unused
2008-04-01 22:48:24.129 AO: dropping back audio_buffer_unused
2008-04-01 22:48:24.352 AO: dropping back audio_buffer_unused
2008-04-01 22:48:24.545 AO: dropping back audio_buffer_unused
2008-04-01 22:48:24.642 AO: dropping back audio_buffer_unused
2008-04-01 22:48:56.892 NVP::AddAudioData():p1: Audio buffer overflow, 
audio data lost!
2008-04-01 22:49:13.540 NVP::AddAudioData():p1: Audio buffer overflow, 
audio data lost!
... repeated many more times, whenever sync gets bad...
2008-04-01 22:49:35.299 NVP::AddAudioData():p1: Audio buffer overflow, 
audio data lost!
2008-04-01 22:49:35.523 NVP::AddAudioData():p1: Audio buffer overflow, 
audio data lost!
2008-04-01 22:49:35.744 NVP::AddAudioData():p1: Audio buffer overflow, 
audio data lost!
2008-04-01 22:49:38.811 TV: Attempting to change from 
WatchingPreRecorded to None

Any ideas?

DaveD.