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

Erik Slagter erik at oldconomy.com
Tue Aug 12 11:30:24 CEST 2003

> I had a look at the man pages of v4lctl but don't see its relevance to
> my problem.

It's about v4lctl volume ..
> > 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).
> My card has a Philips tuner but I guess this is not what you mean.

No, most cards have a Philips tuner.

> Moreover I don't use the btaudio driver which, if I understand
> correctly, would provide the sound directly from the TV card.

Yes, in the case of a bt878 ic.

> I just noticed that a tvaudio driver is loaded, but I don't know what
> is its function.

Try to remove it and look what happens ;-)

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

> Do you mean the parameters which are listed by modinfo -p... ?

No, mplayer arguments. See man mplayer, look for "-tv". For some v4l2
boards you need to supply these.

> > 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.
> I get some output only from 
>         cat -tv /dev/dsp
> However, I get it also without running xawtv. Does it explain
> anything?

If it says "^@^@^@^@^@^@^@^@^@" etc. then the sound is mute. Only when
this is not (anymore) the case there is sense in experimenting further
with mencoder.

> I enclose as attachment (I hope they are allowed on this list):
> the output of v4l-info
> the output of lsmod
> the fragments of dmesg which seemed relevant to me

Please remember for further reference ;-) it is a bt878 ic. IIRC that is
a bt848 with some enhancements like audio grabbing over the pci bus, so
the btaudio module does make sense.

If you have the btaudio module loaded /dev/dsp1 or /dev/dsp2 should have
been enabled and you may get your tv audio from there (see my story
about philips cards). This yields better a/v sync and quality and also
avoids setting up your soundcard.

BTW about recording video tapes in general: are you aware that
pre-recorded video tapes have macrovision copy protection? And also that
VCR signals have _very_ poor synchronisation (induced by the mechanical
nature of the flying head and surrounding parts).

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