[mythtv] BTAudio Module

Bruce Markey mythtv-dev@snowman.net
Sat, 07 Dec 2002 20:36:31 -0800

Harondel J. Sibble wrote:
> On 7 Dec 2002 at 14:14, Harondel J. Sibble wrote:
>>I am assuming it works with the non VE version as I've gotten this is the
>>syslog during btaudio module loading at various times.
> Hmmm... something is working....
> I startup mythv and go into PiP mode,  with the primary card displaying video 
> and audio, I then switch windows by typing "n" and now I get the video from 
> tuner 2 along with the sound.  
> This is after running setup again and telling it to use /dev/dsp2 (or maybe 
> /dev/dsp3 I can't remember) for the second tuner.
> Now before I celebrate is there any other way this could work without using 
> the btaudio module since I no longer have an audio cable between the ATI TV 
> Wonder and my SBlive?

btaudio may have been working all along but it isn't obvious
how to "hear" it. In short, the BT card doesn't have speakers
so you need to use something like "aplay" to read from
/dev/dsp* and write to PCM on your sound card so you can
hear it through your speakers.

A DSP is what takes an analog signal and digitizes so MythTV
(in this case) can store it in a file. To do this, myth needs
to read data from a DSP output on /dev/dsp* . There is only
one DSP source on your card which digitizes the input marked
for capture. This is why you need two DSPs for two tuners.

When you use xawtv, your line-in is redirected to line-out
without needing the DSP (this is why you need to mute line-
in before you start myth). If you plug a second tuner into
aux then unmute and set the volume for aux you can hear the
sound redirected to line-out from "xawtv -c /dev/video1".
However, that still doesn't mean there is a DSP generating
data that can be stored in a file.

So, here is how you can test that audio is going through
the /dev/dsp* devices properly for myth to use them. I'll
assume here that the DSP for the second card is on /dev/dsp1

Open several shells ;-).

   xawtv -c /dev/video

   xawtv -c /dev/video1

Change channels so that you can easily tell which channel
matches what sound. Mute audio sources so that you hear
nothing from either TV channel. Next:

   aplay /dev/dsp

You should hear the audio that goes with /dev/video

   ^C # kill aplay
   aplay /dev/dsp1

You should hear the audio that goes with /dev/video1

Once this works correctly, myth will work correctly. This
test is also useful for setting the volume levels so they
are close to equal between the two tuners.

--  bjm