[mythtv-users] 32khz AC3 Streams was: Sound problem with AC3 passthrough

[Steve Hodge]

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
stream.

I know in my case that the soundcard can only output 44.1kHz and 48kHz
spdif. Maybe it's the same with the nforce2?

Steve