[mythtv-users] 32khz AC3 Streams was: Sound problem with AC3 passthrough
adeffs.mythtv at gmail.com
Tue Jun 6 19:14:20 UTC 2006
On 6/6/06, Steve Hodge <stevehodge at gmail.com> wrote:
> On 6/6/06, Rob Baumstark <rbaumstark at gmail.com> wrote:
> > I had been just running '-ac hwac3' with no comma and no -ao option.
> FYI, the comma tells mplayer to fall back to the default codec if hwac3 fails.
> > No options
> > Plays perfectly fine. Audio is in sync and at the right pitch/speed.
> But downmixed to stereo - not ac3 passthrough, right?
> > '-ac hwac3'
> > Both the audio and the video play back at high speed - they stay in
> > sync. The audio is also quite high pitched. Here I'm assuming it's
> > just speeding the AC3 up to 48khz (and the video along with it)
> > instead of resampling it properly. This is what MythTV does.
> I get something like this if I use "-ao alsa:device=spdif-hw". The
> video plays at normal speed, but the audio plays fast with regular
> pauses. I think my system is syncing audio to video while yours is
> syncing video to audio. Both are getting the audio sample rate wrong.
> > '-ao alsa:device=default -ac hwac3'
> > The video plays fine, at the proper framerate. My receiver
> > indicates it's receiving a 48khz PCM stream, and outputs a very loud
> > popping kind of sound, so I didn't let it play for long.
> I get this if I use "-ao alsa:device=spdif". What I think is happening
> is that alsa is trying to convert the AC3 stream to 48kHz as if it
> were a PCM stream. Obviously this makes a complete mess of the AC3
> I know in my case that the soundcard can only output 44.1kHz and 48kHz
> spdif. Maybe it's the same with the nforce2?
I was under the impression that AC3 passthrough did not touch the AC3
stream, thus the "passthrough" convention.
In other words, the software should not care what the AC3 stream
holds, onec it sees the AC3 header it should just pass the stream
untouched through the SPDIF output. Is it possible your decoder is
unable to handle the 32khz stream?
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