[Alsa-user] Re: Recording in/out of an oss program?

[Andrew B. <aa...@ci...>]

>> I have a proprietary program that uses OSS for sound i/o. I have alsa 
>> installed.
>> I would like to record all of its sound i/o. (It's a VoIP phone. and I want to 
>> record my conversations).

>This is probably what you need ('vsound' package):
>Name: vsound
>Version: 0.6-2mdk
>Size: 44 KB
>Summary: Virtual loopback cable for audio
>Description: VSound is sort of like a 'virtual audio loopback cable'. That is,
>it allows you to record the output audio stream of a program (similar to
>connecting a loopback cable to the line in and line out jacks on the sound
>card, and recording the sound from the line in jack, but without the DA/AD
>conversion losses). One possible use for this application is as part of a
>RealAudio to WAV file converter.

I do exactly this with aoss and the alsa file plugin. Its a bit of a hack
but it works with mplayer. 

.asoundrc:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

pcm.oss_file {
	type plug 
	slave {
	  channels 2
	  #rate 44100		# syntax error
	  pcm {
	    type file
	    file /tmp/alsa_pipe.wav
	    slave {
	      pcm hw:0		# pick one
	      #pcm null		# pick one
	    }
	  }
	}
}

# define default alsa device

pcm.!default pcm.oss_file

# define default oss device

pcm.dsp0 {
    type plug
    slave {
      pcm oss_file
    }
}

ctl.mixer0 {
    type hw
    card 0
}
::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

Then just:
  rm -vf /tmp/alsa_pipe.wav
  aoss mplayer <avifile>

::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

There are some problems:

  The file seems to never be erased as the alsa API says it should, it seems
  that alsalib just seeks back to the beginning and overwrites each time the
  oss_file device is opened. My app needs to see the file changing so I must
  always rm the file before use.

  The file has no wav headers so its impossible to know what the sample rate
  etc is, I wish there were an option to the file plugin that wrote wav headers
  or that the 'rate 44100' parameter worked (this is probably just my asoundrc
  error but I can't figure it out). Mplayer has an option to force the sample rate
  so I am able to work around this. For other apps I might have problems...

  The latency is bad, because probably no one intended this to work 'live' like
  I am using it. I have to use a 500msec ring buffer to prevent dropouts. Again
  mplayer allows me to delay video 500msec to work around this. Other apps...

What I really need is a plug that take a playback stream and provides a capture
stream from it. Does anyone know if this exists? From the alsalib docs, the
file plugin was as close as I could come.