[mythtv-users] Audio - Why Does MythTV Try To Use /dev/dsp1?

[Karsten Jeppesen]

Drew Tomlinson wrote:

> I almost have my first Myth box up and running.  However, I can't get 
> audio when watching LiveTV.  Myth pauses a moment and then tells me 
> that /dev/dsp1 is not available, and give me the option to continue 
> without audio.
>
> My box has a WinTV 250 and SoundBlaster Audigy card on a Gentoo 2.6.11 
> platform.  I'm using ALSA and can get sound both from 'aplayer' and 
> 'aoss'.  I have /dev/dsp0 but not /dev/dsp1.  How do I get MythTV to 
> use /dev/dsp0?  Or how can I tell what's using /dev/dsp0 causing Myth 
> to try /dev/dsp1?  This whole sound thing confuses the hell out of me.


I have spend some time on that account. My setup is a FC3 with MythTV 
0.18.1 (the latest - but not that it matters)
First - Alsa is not fully supported by MythTV. Only the output part can 
be configured.
Second - You have two places to select sound. One is for the capture 
card. That configuration lives in mythtv-setup. The other is for output 
sound. That configuration lives in mythfrontend. Which makes sense - The 
capture is run by the backend and the outpt from the frontend.

Now - since MythTV does not support ALSA for the capture part, then you 
are relying on ALSA to adapt to the older OSS (Open Sound System) interface.
ALSA does that by means of a module called snd_pcm_oss.
The old depreciated OSS interface uses device files called /dev/dsp# and 
/dev/adsp#  where # is a umber from 0 tp 7 inclusive. 0 sometimes being 
just absent.

Unfortunately MythTV doesn't fully support the OSS either. You will 
never see /dev/adsp# in the choises. And in my case - that is precisely 
where my capture sound is to be found. If I am using the capture 
facility of my video capture card, that is.

So what to do?

Well - ALSA will allow you to remap dsp and adsp devices to your liking, 
and I have done that. But for a test it is much easier to rape the 
system. Let us assume that you have /dev/dsp, /dev/dsp1, /dev/adsp, 
/dev/adsp1.
Now cd to /dev
Make links (oh that is a cheap trick)
ln -s /dev/adsp /dev/dsp2
ln -s /dev/adsp1 /dev/dsp3

And restart MythTV. Now you can choose your adsp devices. Because Myth 
will now list them as dsp2 and dsp3.
If you are interested, then you may be able to pull some tidbits out of 
my story of how I am progressing using ALSA from my rants 
<http://jeppesens.com/mythtv.html>.

Karsten