[mythtv] AC3 passthrough

Doug Larrick doug at ties.org
Tue Dec 2 08:08:22 EST 2003

On 12/02/03 02:07:11, Jason Hoos wrote:

> It actually happens on live TV as well.  Is the ABC affiliate by you  
> a 720p station?  If so, does it seem to work well during live TV?

I just watched 5 minutes or so of ABC (720p) and audio worked fine.

> I've actually done some checking by putting a call into
> audiooutputalsa.cpp to check how much of the sound card's buffer is  
> full (something like snd_pcm_avail_update() I think?), and the  
> dropouts seem to correspond to times when the buffer is mostly empty  
> (which makes sense).

You're not seeing "Audio buffer overflow" messages or anything like  
that, are you?  I was having problems with OSS sound when I would watch  
a 5.1-channel program (PBS mostly) that I diagnosed as a too-small  
audio buffer in audiooutputoss.  I would get overflow messages, and  
eventually it would get lost and the audio would turn to white noise  
(not pleasant).  Tripling the OSS audio buffer size fixed it, though  
since switching to ALSA fixed it I never cleaned it up & sent a patch.

It could also be that your ABC station's MPEG stream has the audio as  
relatively large packets, relatively far apart.  More overall buffering  
(time delay) would help with that.

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