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

Drew Tomlinson drew at mykitchentable.net
Tue May 17 08:27:28 UTC 2005


On 5/16/2005 10:17 AM Karsten Jeppesen wrote:

>
>
> 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>. 

Thanks for your detailed info.  I will save your email and use as a 
reference until I have things working the way I want.

Cheers,

Drew

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