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

Rob Baumstark rbaumstark at gmail.com
Wed Jun 7 04:53:29 UTC 2006

> ALSA is resampling to 48k because my Denon 3806 on-screen display is
> showing PCM 48,000 but some funkyness has happened between now and then

Ok - I can get that part to work too - however PCM output over digital
is only capable of 2-channel.  This is not an option if I want to keep
the 5.1 sound intact for my HD and premium channels, and I don't want
to have to go into setup and keep changing the audio passthrough
depending on what channel I'm watching (same effect as running mplayer
with/without -ac hwac3).

> first, i tried -ao alsa:device=default (ok)
> then i tried above with -ac hwac3 (still ok) as seen in the second
> bracket of output

That second attempt of yours has gotten me curious - that appears to
be what I want to have.  What sound card are you using, it appears to
support more than just 48khz out its digital port.  Looking around on
the ALSA site at sound-card support, the driver for my card (nForce 2
/ soundstorm) it specifically says that output is always resampled to
However, just as an example here is the alsa page for the VIA audio
driver - which does not appear to have the 48khz limitation.

If buying a card that can output 32khz on its digital port ends up
being my only solution, well then its the only solution and I'll have
to go buy a card.  If anyone can suggest a sound card with good linux
support and 32khz support (and 48khz, but I doubt that will be an
issue) I'll go pick one up.

> i removed liba52 from system and tried it (strangely, still ok) the
> output from mplayer is not listed below from this test but it DID work fine
> HOWEVER, i reinstalled liba52, rebooted for kicks and grins, recompiled
> myth fron the .19-fixes SVN branch after pulling in the recent libmythtv
> fixes to test other things and tried your clip again
> WITHOUT -ac hwac3, plays fine (see third block of output)
> WITH -ac hwacs, jittery scratchy garble which could only be 32k arriving
> at the receiver (see 4th block of output)

Your second attempt would seem to contradict that conclusion, as it
seems to me as though your second attempt had your receiver playing
the 32khz AC3 stream just fine.  But I'm just guessing based on the
mplayer output without seeing your receivers display, so maybe I
missed something.

> i'm kinda stumped right now and my head is bobbing so i'll continue
> tommorrow afternoon when i can focus alittle more
> --
> mw

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