[mythtv-users] HD 720p Audio/Video sync problem - some times

DaveD mythtv at guiplot.com
Tue Dec 11 04:14:45 UTC 2007


I am having trouble with A/V sync on some HD shows recorded from our PBS 
channel.  It is the only channel I get that broadcasts 720p.  Some shows 
have the problem, some do not.  What happens is the video continuously 
races ahead of the sound and Myth constantly adjusts, some times slowing 
the video, some times speeding up (and dropping parts of) the sound.  
It's very unwatchable.

Good news is I can watch the recordings with Xine or Mplayer.  Both work 
fine.  Myth works fine on all other HD recordings (all other HD channels 
are 1080i).  All SD works fine.

I am running a FE/BE combo myth system on a dual core athlon with 2Gb 
RAM, Nvidia 7600, dual SATA.  I am running Axel's 0.21-171_trunk_r14785 
RPM on an up-to-date x86_64 FC7 (2.6.23.1-21 kernel) with 
ALSA:passthrough sound.  I tried switching sound to /dev/dsp, no 
change.  I tried a complete install of Ubuntu, which comes with Myth 
0.20.2.  Same problem, exactly.  I also have two 64-bit athlon single 
core systems, both with older Nvidia cards, both running the same 
version of FC7 and Myth (frontend only), both have the same problem.

I have seen similar posts but no solutions yet.  I've included 
Myth-frontend and Mplayer's output, below.  Mplayer had the exact same 
output on both a "good" and "bad" file while playing them both 
successfully.  Myth-frontend used different codecs (see below).   I have 
not found any documentation on Myth's new Playback Profiles (codec 
selection?) screen.  I find the best results using their default CPU++ 
setting, but I've tried the three they provide, with no change in this 
problem and decreased performance (or functionality) in other areas with 
the other choices.

Anyone have any suggestions?

DaveD

Myth-frontend's output during playback of problem recording:
2007-12-10 19:14:48.202 TV: Attempting to change from None to 
WatchingPreRecorded
2007-12-10 19:14:48.284 AFD: Opened codec 0xccf9d0, id(MPEG2VIDEO) 
type(Video)
2007-12-10 19:14:48.285 AFD: Opened codec 0xcca770, id(AC3) type(Audio)
2007-12-10 19:14:48.287 Opening ALSA audio device 'spdif'.
2007-12-10 19:14:48.305 DPMS Deactivated
2007-12-10 19:14:48.325 AudioOutput Warning: Mixer attach error -2: No 
such file or directory
                       Check Mixer Name in Setup: '/dev/mixer'
2007-12-10 19:14:48.653 VideoOutputXv: XVideo Adaptor Name: 'NV17 Video 
Texture'
2007-12-10 19:14:50.160 Realtime priority would require SUID as root.
2007-12-10 19:14:50.161 TV: Changing from None to WatchingPreRecorded
2007-12-10 19:14:50.268 Video sync method can't support double framerate 
(refresh rate too low for bob deint)
2007-12-10 19:14:50.274 Video timing method: USleep with busy wait
2007-12-10 19:14:50.778 AO: dropping back audio_buffer_unused
... more of these, but they stop after a few seconds...
2007-12-10 19:14:53.734 AO: dropping back audio_buffer_unused
2007-12-10 19:14:54.827 DPMS Reactivated.

Myth-frontend's output during playback of recording that works well:
2007-12-10 19:18:03.201 TV: Attempting to change from None to 
WatchingPreRecorded
2007-12-10 19:18:03.284 AFD: Opened codec 0x56b1c10, id(MPEG2VIDEO) 
type(Video)
2007-12-10 19:18:03.285 AFD: Opened codec 0x56f1980, id(AC3) type(Audio)
2007-12-10 19:18:03.286 Opening ALSA audio device 'spdif'.
2007-12-10 19:18:03.290 AudioOutput Warning: Mixer attach error -2: No 
such file or directory
                       Check Mixer Name in Setup: '/dev/mixer'
2007-12-10 19:18:03.304 DPMS Deactivated
2007-12-10 19:18:03.409 VideoOutputXv: XVideo Adaptor Name: 'NV17 Video 
Texture'
2007-12-10 19:18:04.489 Realtime priority would require SUID as root.
2007-12-10 19:18:04.489 TV: Changing from None to WatchingPreRecorded
2007-12-10 19:18:04.591 Video sync method can't support double framerate 
(refresh rate too low for bob deint)
2007-12-10 19:18:04.593 Video timing method: USleep with busy wait
2007-12-10 19:18:04.729 AO: dropping back audio_buffer_unused
... more of these, but they stop after a few seconds...
2007-12-10 19:18:05.021 AO: dropping back audio_buffer_unused
2007-12-10 19:18:30.479 DPMS Reactivated.


Mplayer's console output (most of, same on both recordings):
Playing 2095_20071129060000.mpg.
TS file format detected.
VIDEO MPEG2(pid=1984) AUDIO A52(pid=1985) NO SUBS (yet)!  PROGRAM N. 1
VIDEO:  MPEG2  1280x720  (aspect 3)  59.940 fps  38810.4 kbps (4851.3 
kbyte/s)
==========================================================================
Opening video decoder: [mpegpes] MPEG 1/2 Video passthrough
VDec: vo config request - 1280 x 720 (preferred colorspace: Mpeg PES)
Could not find matching colorspace - retrying with -vf scale...
Opening video filter: [scale]
The selected video_out device is incompatible with this codec.
Try appending the scale filter to your filter list,
e.g. -vf spp,scale instead of -vf spp.
VDecoder init failed :(
Opening video decoder: [libmpeg2] MPEG 1/2 Video decoder libmpeg2-v0.4.0b
Selected video codec: [mpeg12] vfm: libmpeg2 (MPEG-1 or 2 (libmpeg2))
==========================================================================
==========================================================================
Forced audio codec: hwac3
Opening audio decoder: [hwac3] AC3/DTS pass-through S/PDIF
No accelerated IMDCT transform found
hwac3: switched to AC3, 384000 bps, 48000 Hz
AUDIO: 48000 Hz, 2 ch, ac3, 384.0 kbit/25.00% (ratio: 48000->192000)
Selected audio codec: [hwac3] afm: hwac3 (AC3 through S/PDIF)
==========================================================================
AO: [alsa] 48000Hz 2ch ac3 (1 bytes per sample)
Starting playback...



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