Hmmm... The API says: "Whenever a buffer is "used" by the program it should called VIDIOCSYNC to free this frame up and continue. to add:VIDIOCSYNC takes the frame number you are freeing as its argument." According to that, if you call VIDIOCSYNC on a frame, you are saying to the driver "I'm done with this frame". I'd also be a little more confused because of the couple drivers I've looked at, VIDIOCMCAPTURE doesn't return until they've pulled in and decoded a frame. Also the source code to the zapping program puts the call to VIDIOCSYNC in a function called tveng_dequeue which isn't called until it is done with the buffer. On Friday 15 February 2002 01:14 am, you wrote: > Hi! > > On Thu, 14 Feb 2002, Joe Burks wrote: > > Anyway, if I read that code right the answer is that VIDIOCMCAPTURE ioctl > > must be called once for every frame you capture. If the frame in > > question is not yet available because it is spooling, the ioctl will > > block until the image is available. > > Yes, VIDIOCMCAPTURE must be called for every frame. > No, VIDIOCMCAPTURE doesn't block. VIDIOCSYNC blocks. > > To achieve the full capture rate the application usually has to call > VIDIOCMCAPTURE-for-frame-n+1 before frame n finishes, i.e. before the > VIDIOCSYNC-for-frame-n. To make this possible the driver must offer more > than one capture buffer and must be able to queue up several incoming > VIDIOCMCAPTURE calls - and dequeue them on every beginning frame > (interrupt-driven in case of capture cards).
