[MPlayer-users] Re: recording from video tapes (a novice question)

Erik Slagter erik at oldconomy.com
Mon Aug 11 20:50:54 CEST 2003

> > Check that you're able to record the sound you hear with _any_ sound program. 
> > Even a program that visualizes sound will be OK, as long as it does not 
> > visualize data which it plays (e.g. no xmms, but for example krecord). 
> I use Knoppix 3.2 of 2003-05-03 as the testbed. It doesn't contain
> krecord, but has audacity. However audacity complains about its
> default settings, it says that /dev/dsp is invalid playback device. I
> am more and more confused :-(.

Keep in mind that your tv capturing card also has a mixer, which is
accessible via the v4l interface, not via /dev/mixer etc. Xawtv is able
to manipulate the settings, as the supplied command line util v4lctl.

Depending on the type of card you need to set up a loop from the tv
capturing card to an input of your sound card (makes easy testing) or
read your audio from the corresponding audio device.

To examplify:

If you have an bt848 card, you only have analogue audio output, so you
need to connect the audio output to an input on your soundcard. Using
xawtv you should be able to check if your setup is ok. On xawtv set the
volume to max and make sure audio is not muted.

If your have a philips card, you will want to fetch the audio over the
pci bus, because the card goes through great lengths to ensure the video
and audio are deliverd synchronously. In that case also use xawtv to set
the v4l volume settings, and locate the extra sound and mixer devices.
Usually they are /dev/dsp1 and /dev/mixer1, but this may vary depending
on your setup. Now use sox to copy the input from /dev/dsp1 using
samplerate 32 Khz (!) to /dev/dsp and you should be able to hear the
audio via the "pcm" output of your soundcard. If that works, you can try
to record video and audio with e.g. mencoder, making sure that audio is
grabbed from your "extra" sound device (/dev/dsp1).

Also check the options "forchechans" and "forceaudio", the are required
on some v4l2 modules.

If none of this works, try, while running xawtv, "cat -tv /dev/dsp" and
"cat -tv /dev/dsp1", etc. This will tell you which audio devices are
available and which actually deliver sound data.

What capturing card do you have (or better: what chip is on it?)

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