How to read the sound card ?

How to read the sound card ?

[Michaël Todorovic]

hello,
I want to read the data on the sound card (to do a fft and other 
things). I have first tried the capture stream with snd_pcm_readi and 
everything is working. My problem is that I want to read the sound 
output (pcm or mixer). For example, I want to read the sound that xmms 
or mplayer is writing on the sound card. If I just change 
SND_PCM_STREAM_CAPTURE to SND_PCM_STREAM_PLAYBACK in snd_pcm_open, 
snd_pcm_readi fails.

So my question is : how can I read the sound output with the alsa-lib ?

Thank you

-------------------------------------------------------------------------
Take Surveys. Earn Cash. Influence the Future of IT
Join SourceForge.net's Techsay panel and you'll get the chance to share your
opinions on IT & business topics through brief surveys -- and earn cash
http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV

Re: How to read the sound card ?

[Benoit Fouet]

Hi,

I think the simpler way is to write a plugin for alsa, which will take
place in the plugin chain, just before outputing the sound.
The last time i did that, you couldn't do it if using softmix (which has
to be directly plugged to hw) but maybe it's possible now...
There is a doc written on how to write an ALSA plugin, that should help
you do that ;)

Regards,

-- Ben


Michaël Todorovic wrote:

>hello,
>I want to read the data on the sound card (to do a fft and other 
>things). I have first tried the capture stream with snd_pcm_readi and 
>everything is working. My problem is that I want to read the sound 
>output (pcm or mixer). For example, I want to read the sound that xmms 
>or mplayer is writing on the sound card. If I just change 
>SND_PCM_STREAM_CAPTURE to SND_PCM_STREAM_PLAYBACK in snd_pcm_open, 
>snd_pcm_readi fails.
>
>So my question is : how can I read the sound output with the alsa-lib ?
>
>Thank you
>
>-------------------------------------------------------------------------
>Take Surveys. Earn Cash. Influence the Future of IT
>Join SourceForge.net's Techsay panel and you'll get the chance to share your
>opinions on IT & business topics through brief surveys -- and earn cash
>http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV
>_______________________________________________
>Alsa-devel mailing list
>Alsa-devel@lists.sourceforge.net
>https://lists.sourceforge.net/lists/listinfo/alsa-devel
>  
>

-------------------------------------------------------------------------
Take Surveys. Earn Cash. Influence the Future of IT
Join SourceForge.net's Techsay panel and you'll get the chance to share your
opinions on IT & business topics through brief surveys -- and earn cash
http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV

Re: How to read the sound card ?

[Takashi Iwai]

At Mon, 31 Jul 2006 09:23:14 +0200,
Benoit Fouet wrote:
> 
> Hi,
> 
> I think the simpler way is to write a plugin for alsa, which will take
> place in the plugin chain, just before outputing the sound.
> The last time i did that, you couldn't do it if using softmix (which has
> to be directly plugged to hw) but maybe it's possible now...

The situation hasn't been changed much.  But it's basically doable.
For example, using a file plugin, you can achieve like "tee" command,
and on one side, you can put a FIFO.

It'd be difficult, though, if you'd like to implement it as a virtual
PCM capture device.


Takashi

-------------------------------------------------------------------------
Take Surveys. Earn Cash. Influence the Future of IT
Join SourceForge.net's Techsay panel and you'll get the chance to share your
opinions on IT & business topics through brief surveys -- and earn cash
http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV