Trent Piepho wrote: > > 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. I am not sure of the status of bttv-0.8.x at the moment, but with bttv2 (bttv-v4l2.sf.net), you can capture vbi and image surfaces with streaming buffers. All the buffers are timestamped, so it is trivial to match up the correct vbi buffer with the correct image buffer. -justin
