[mythtv-users] how to tell if 5.1 audio channels mapped correctly?

[Dan Christensen]

Jean-Yves Avenard <jyavenard at gmail.com> writes:

> On 5 November 2010 02:57, Dan Christensen <jdc at uwo.ca> wrote:
>
>> I found a test video at
>>
>>  http://www.tfm.ro/ac3/download/test_ac3.rar
>>
>> It plays with the correct channels in myth, but with the channels
>> incorrect with mplayer, xine and vlc.
>
> That's surprising ...
> That it's wrong is one thing, but I would expect it to be wrong everywhere

That's what I thought.  Can someone test the file in mythtv as
well as one of those other players?  I've put an unpacked version
here for easy direct download:

  http://jdc.math.uwo.ca/tmp/Test-AC3-v2.0.avi

>> Am I just trying poorly encoded clips?
>
> That's a possibility

Is it reasonable that a strange encoding would cause the channel mapping
to be wrong with one program and correct with another?

Hmm, some googling shows that mplayer has had trouble with this kind of
thing in the past, in a way that is dependent on the audio codec used.
This is in part because different codecs use different channel
orderings, but also because mplayer sometimes uses a library like ffmpeg
which also has different conventions.  So maybe I'm just up against some
bugs in mplayer?  But I found problems with vlc and xine too, so that
makes this explanation hard to believe.

> I have some test clip there you can try:
> http://www.avenard.org/files/media/videotest/audiotest/

This one

  idch_AviaSurroundTest-AAC.mkv

and the DTS version, both play fine with mythtv, but mplayer and xine
get them both wrong.

I should have mentioned in my initial post that to try to make the hdmi
output the default for all applications, I created /etc/asound.conf
which contains

  pcm.!default {
  type hw
  card 0
  device 3
  }

That didn't actually make mplayer produce sound, so I have the following
in mplayer.conf:

ao=alsa:device=hdmi
channels=6

Do these settings look reasonable?

What do you use to test the audio-only files?  Can they be played with
myth's Internal player, so I can further test it?

> This is the motherboard on which I test all the audio with myth..

I thought so.  I bought it because of your recommendation regarding
VDPAU...

I wonder if something like this is relevant, from 

  http://www.cse.ohio-state.edu/~bondhugu/alsamch.shtml

  A common issue with some ICH5 chips is that the Center and LFE
  channels are swapped with rear channels. To fix this, you'll have to
  edit a section of /etc/alsa/cards/ICH4.conf to make it like
  /etc/alsa/cards/ICH.conf.

He's probably referring to this part of ICH.conf:

                ttable.0.0 1
                ttable.1.1 1
                ttable.2.4 1
                ttable.3.5 1
                ttable.4.2 1
                ttable.5.3 1

Just out of curiosity, are you using hdmi for audio output?  Do you
think that could be a factor?  (And have you found a way to make the
audio work when the dpms screen saver kicks in?)

Thanks for any help!

Dan