[mythtv-users] playback problems with multiple AC3 streams

[Matt W]

Hi --

so my last post was a bit desperate but I think I've narrowed down
where the issues lie.  It's not 720p or 1080i playback, etc; it really
seems to be audio-related.

If I set myth to do 5.1 sound, and tune a program with 3 AC3 audio
streams, I can't get Dolby Digital sound to properly sync.  Example of
playing back a NOVA episode from KQED-HD. mythfrontend log:

2010-02-10 12:18:47.810 TV: Attempting to change from None to Watching
WatchingPreRecorded
2010-02-10 12:18:48.074 AFD: Opened codec 0x7f206c9b6820,
id(MPEG2VIDEO) type(Video)
2010-02-10 12:18:48.074 AFD: codec AC3 has 6 channels
2010-02-10 12:18:48.075 AFD: Opened codec 0x7f206c9aa400, id(AC3) type(Audio)
2010-02-10 12:18:48.075 AFD: codec AC3 has 2 channels
2010-02-10 12:18:48.076 AFD: Opened codec 0x7f206c9d6b80, id(AC3) type(Audio)
2010-02-10 12:18:48.076 AFD: codec AC3 has 2 channels
2010-02-10 12:18:48.077 AFD: Opened codec 0x7f206c9824a0, id(AC3) type(Audio)
2010-02-10 12:18:48.080 Opening audio device 'spdif'. ch 2(6) sr 48000 (reenc 0)
2010-02-10 12:18:48.081 Opening ALSA audio device 'iec958:{ AES0 0x02 }'.
2010-02-10 12:18:48.103 Opening audio device 'spdif'. ch 2(6) sr 48000 (reenc 0)
2010-02-10 12:18:48.104 Opening ALSA audio device 'iec958:{ AES0 0x02 }'.
2010-02-10 12:18:48.196 Opening audio device 'spdif'. ch 2(2) sr 48000 (reenc 0)
2010-02-10 12:18:48.196 Opening ALSA audio device 'iec958:{ AES0 0x02 }'.

...at that point, I don't see buffer or audio problems in mythfrontend
log, though.


What's interesting is, when trying another channel (KGO-HD, ABC), I
see an example of 3 AC3 streams, and i have no trouble getting DD lock
and good sound there...

2010-02-10 12:22:21.354 AFD: Opened codec 0x7f206c01e190,
id(MPEG2VIDEO) type(Video)
2010-02-10 12:22:21.354 AFD: codec AC3 has 6 channels
2010-02-10 12:22:21.355 AFD: Opened codec 0x7f206cfe0db0, id(AC3) type(Audio)
2010-02-10 12:22:21.355 AFD: codec AC3 has 1 channels
2010-02-10 12:22:21.356 AFD: Opened codec 0x7f206cfdebe0, id(AC3) type(Audio)
2010-02-10 12:22:21.356 AFD: codec AC3 has 0 channels
2010-02-10 12:22:21.357 AFD: Opened codec 0x7f206c9d47c0, id(AC3) type(Audio)
2010-02-10 12:22:21.407 NVP(6): Prebuffer wait timed out 30 times.
2010-02-10 12:22:21.417 Opening audio device 'spdif'. ch 2(6) sr 48000 (reenc 0)
2010-02-10 12:22:21.417 Opening ALSA audio device 'iec958:{ AES0 0x02 }'.

BUT...note that it's only a total of 7 audio channels when you add the
3 streams together.

So it looks like the system (whatever that means) can't handle the 3
AC3 streams that contain a total of 10 audio channels.  Is it the
speed of the video renderer? Is this just my hardware isn't fast
enough, or perhaps the audio drivers are being maxed out and/or aren't
fast enough?

I actually find this more interesting than frustrating.  Trying to
stay Myth-related... is there a way I can configure a recording
schedule to only grab one (preferred) audio stream?  Or maybe do this
in playback?

thanks!