[mythtv] Separating CAPTUR and Capture in OSS

Bruce Markey bjm at lvcm.com
Tue Mar 4 18:00:38 EST 2003

Tom Panning wrote:
> When I try to watch live TV with MythTV, I hear both the sound for the live 
> feed (what Myth is recording) and what's being played from the buffer. Here's 
> what I'm using:
> * SB Live sound card (with OSS sound drivers)
> * Hauppage WinTV card
> * CVS version (today) of MythTv
> * Debian unstable
> I know that the Faq and the How-to mention this problem, but in both documents 
> the solution appears to be specific to alsa drivers. I understand what has to 
> be done with the mixer in order to get it to work, but I can't seem mute the 
> "CAPTUR source" without muting the "Capture mixer" (as they are referred to 
> in section 17.11 of the HOWTO).
> After futzing with the mixer quite a bit, here's what I've been able to 
> discover:
> 1) There are 13 mixer controls: Volume, Pcm, Speaker, Line*, Microphone*, CD*, 
> IGain*, OGain, Line1*, Digital1, PhoneIn*, PhoneOut, and Video*. (an asterisk 
> (*) means that I can record this channel)

I believe IGain (or possibly OGain) is the equivalent of ALSA's
"Capture" to control to level going into the DSP. For OSS, you
can do the same kind of test from section 17.11 by subsitiuting
"sox" for "aplay" and your favorite mixer in place of "alsamixer".
"man sox" to determine the options it will need.

> 2) When I listen to mp3's using xmms, all of the controls can be muted except 
> for Pcm and OGain; I can set any channel to be the recording channel and it 
> does not affect playback. Moving the volume control in xmms moves the Pcm 
> slider. (I have no idea why I can muting the Volume control has no effect).

Since this is an SB Live!, is it possible you are going out
through an output other than line-out/speaker?

> 3) When I use xawtv, all of the controls can be muted except for IGain and 
> OGain; Line must be set to record (but the mute and volume setting have no 
> effect).
> 4) In MythTV, if I use the xawtv settings (see #3), then I hear the live feed 
> and not the playback. If I unmute the Pcm control, then I hear both the live 
> feed and the playback. If I then mute the IGain control (or turn it's volume 
> down to zero) then I hear just the playback for a few seconds until I hit the 
> point where IGain was muted, and then there is no sound.

If it turns out that you really can't mute the analog audio
passthru and still record with the DSP, then you may want to
try ALSA. I use a SB Live! with ALSA for MythTV and both the
speaker out and the digital out to a reciever work perfectly.

--  bjm

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