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

Wed Apr 16 03:32:28 UTC 2008

--- DaveD <mythtv at guiplot.com> wrote:

> I've posted this problem a couple of times to the
> users list, 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) so I assume it's something that has
> changed in the way
> they are broadcast and not due to any changes in
> Myth, although I can't
> be certain of that.  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!
> 
=== message truncated ===

I had that problem and it was only on the high-def PBS
channel as the sound would wobble really bad and that
was the only channel. I either turned on or off
Aggressive Sound Card buffering under Setup -> General
and the problem went away. I can't remember which way
since I built a new system.

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