[mythtv-users] using AC3..

Jarod Wilson jcw at wilsonet.com
Mon Nov 1 21:28:14 UTC 2004


On Monday 01 November 2004 10:25, Craig Tinson wrote:
> Just spotted this topic in a previous reply from Jarod..
>
> So thought I'd take it to a new topic..

Good idea, it was kinda buried in that other thread...

> My setup has been running *quite* smoothly with cvs for ages now..  but
> theres something thats bugging me.. and I know its a lack of knowledge
> on my part thats causing it..
>
> I have a decent sound system in my living room.. and my myth box's sound
> card has an s/pdif output.. and although I'm using it.. I *suspect* it
> could sound even better...
>
> I presume using AC3 is the way to go.. but have absolutely *no* idea how
> to go about it..

Issue number one to output AC3 audio, is that you need a video source with AC3 
audio. I believe most DVB stuff contains AC3 audio, but I don't believe 
straight PAL does. I know straight NTSC doesn't. I'm passing raw AC3 to my 
amp on HDTV streams and dvd rips, passing PCM on standard-def TV.

>  From memory.. I must be using OSS Emu.. as myth is still pointing at
> /dev/dsp..

Yup.

> So is there any docs on using *pure* alsa.. and ac3 output for
> myth/alsa/fc2 ? and if not.. could some nice person (looks at Jarod cos
> I know he's doing the same) point me in the right direction?

There's a good Digital Sound Howto page on the mythtv.info site, which is what 
I based my setup off of. I use Mike Dean's fully tweaked out .asoundrc for 
the nForce2 posted there, modified for use with my Audigy (I only had to 
change like five lines) and ALSA:spdif (I believe) as my output device 
instead of /dev/dsp. Despite what it says there and in the linked thread, I 
have both AC3 and PCM passing through to my amp with the "enable AC3 
passthru" option in Myth enabled, not sure if that is because of a change in 
Myth or because of my .asoundrc or what...

http://mythtv.info/moin.cgi/DigitalSoundHowTo

-- 
Jarod C. Wilson, RHCE
jcw at wilsonet.com

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