[mythtv-users] AC3 passthrough not working

[Richard Shaw]

On Sat, Apr 11, 2009 at 9:14 AM, Allen Edwards
<allen.p.edwards at gmail.com> wrote:
>
>
> On Sat, Apr 11, 2009 at 2:22 AM, Glenn Sommer <glemsom at gmail.com> wrote:
>>
>> Hi
>>
>> After a LOT if fighting with this problem... I FINALY made it work!
>>
>> Here's what I did.
>>
>> 1. Upgraded to alsa 1.0.19 (not sure if I needed to though).
>> 2.  added a /etc/asound.conf file containing:
>> pcm.!default {
>>        type plug
>>        slave {
>>                rate 48000
>>                pcm "spdif"
>>                }
>> }
>>
>> 3. Deselected "use video as timebase" in MythTV.
>>
>> Now regular channels work (sending PCM over SPDIF to my receiver), and
>> HD channels with sending AC3/DTS directly to the receiver over SPDIF.
>> :D
>>
>>
>> Maybe there should be some warning with "use video as timebase" - as
>> it does NOT with when using passthrough.. ?
>>
>
> Could you try it without the "rate 48000" line and let me know if it works.
>  It is my belief that adding that line might cause alsa to sample and
> re-encode and thus degrade the data although I am not sure.  It works
> without that line on my system.
> Allen

I agree, setting the rate on a pcm device should have nothing to do
with AC3 passthrough. If the two things are indeed all you have
changed, then it must be the upgrade to alsa 1.0.19. I never needed an
asound.conf file to get passthrough to work, but for PCM sources to
get resampled up to 48KHz to play over spdif. I don't even use that
anymore since Fedora 10. I've gotten pulseaudio to play quite well
with mythTV and it does a much better job of resampling.

Richard