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

Rob Baumstark rbaumstark at gmail.com
Tue Jun 6 00:50:25 UTC 2006

> Are you in the USA?  Do you have a sample of the audio somewhere to
> download?  My FE setup is very similar to yours.  I am running an NF2 mobo
> (ASUS-A7N8X-E DLX) with digi coax out.  I've never had static on any DVD or
> recording from my PVR-x50 cards.

I'm in Canada - so pretty much the same cable system as in the US.
The problem isn't that I have static - the stuff that works properly
is crystal clear.  But 32khz AC3 streams come through at super-high
pitch as they don't get resampled to 48khz properly.  DVD's play fine
with AC3 passthrough as they all use 48khz AC3.  MP3s play fine as
44khz PCM that is resampled by ALSA before being output (using the
asound.conf found in the wiki).  HD channels and premium SD channels
also pass 48khz AC3 through properly.  But SD channels over firewire
from the DCT6200 are coming with 32khz AC3 - it tries to passthrough
because its AC3, but the 32khz part causes problems.

I've tried a couple places to upload a sample MPEG transport stream
with 32khz AC3 audio.  This is captured from test-mpeg2 - playback
with mplayer without passthrough works properly (AC3 is decododed to
32khz PCM, and resampled by ALSA before being output over digital at
48khz PCM).  playback from mplayer with AC3 passthrough has exactly
the same problem as playing an SD channel in MythTV with passthrough
turned on.  But disabling AC3 passthrough in MythTV cuts my 5.1
channels all down to stereo - which is why in my last message I asked
for a way to have AC3 passthrough turn itself off only when non-48khz
AC3 is detected.



If neither of those links work, I'll just host the file off my home
'net connection.  Let me know.

More information about the mythtv-users mailing list