Re: Digitising blanking region

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]



On Wed, 11 Jul 2001, Iain Matthews wrote:
> I am using redhat 7.1 with v4l/bttv-0.7.69 or v4l2/bttv-0.8.18, kernel
> 2.4.6 final. I have tried bttvgrab (0.15.10) and streamer (xawtv 3.55),
> but both will not allow me to increase the capture height beyond 480
> (NTSC).

What you want to do is use the vbi device, e.g. /dev/vbi0.  The bt848
separates capture of the picture area from the capture of the VBI.  This way
you can overlay a clipped and scaled image onto the screen, and still decode
the CC information on line 21, which would be useless if it were clipped or
scaled, and doesn't belong on the screen anyway.

The bttv vbi device isn't the best bit of software.  Last time I checked, you
could only use the read() interface, and there was no buffering.  That made it
very had to avoid losing frames.  In V4L1 there isn't even any way to select
what lines you want, you have to capture and read all of them!  I also don't
remember any way to match up VBI lines to the video frame they came from,
which will probably cause you problems.


If you want to do a quick and dirty trick, you can reprogram the vertical
timing information to bring the VBI into the capture area.  I added an ioctl
to bttv to allow these registers to be reprogrammed.  You will also want to
hack the driver to allow more than 480 lines of capture, unless you don't
mind the bottom of your image getting cut off.





[Index of Archives]     [Linux DVB]     [Video Disk Recorder]     [Asterisk]     [Photo]     [DCCP]     [Netdev]     [Xorg]     [Util Linux NG]     [Xfree86]     [Free Photo Albums]     [Fedora Users]     [Fedora Women]     [ALSA Users]     [ALSA Devel]     [Linux USB]

Powered by Linux