Jacek Dylak wrote:
>
> I use simple AverMedia card with BT878 chip.
>
> I need to capture frame by frame and process each. I try to do this with the
> following code, but I get only 12 frames per second. I need at least 20 fps,
> but I don't what is wrong with my code, or what needs to be change, to get
> frames more frequently.
>
> Is it a matter of coding or the chipset?
>
> I would be very thankful if somebody could help me.
> Jacek
>
> ///////////////////
> //capture code
>
> dev.Open("/dev/video0");
>
> //get memory buffer size
> dev.GetMemoryBuffer(&stMemBuf);
>
> //map memory for frame buffer
> szFrame = (char*) mmap(0,stMemBuf.size,PROT_READ|PROT_WRITE,MAP_SHARED,dev,0);
>
> //set channel to COMPOSITE and mode to PAL
> dev.SetSource(1,VIDEO_MODE_PAL);
>
> //set capture image size and pixel format
> stMemMap.width = IMAGE_WIDTH;
> stMemMap.height = IMAGE_HEIGHT;
> stMemMap.format = VIDEO_PALETTE_GREY;
>
> //capture frame 0
> stMemMap.frame = nFrame;
> ioctl(dev,VIDIOCMCAPTURE,&stMemMap);
>
> while (m_bProcessing)
> {
> stMemMap.frame = nFrame;
> ioctl(dev,VIDIOCSYNC,&stMemMap.frame);
>
> stMemMap.frame = 1 - nFrame;
> ioctl(dev,VIDIOCMCAPTURE,&stMemMap);
>
> ProcessFrame(..); //actually do nothing, simply count up frames
>
> nFrame = 1 - nFrame;
> }
>From the look of that loop you can probably blame that on me! (my
example code)
Try swapping the order of the SYNC(nFrame) and CAPTURE(1-nFrame) pairs
of lines - that way there'll always be a "queued" capture, and you
shouldn't lose any frames assuming your processing isn't taking too
long.
Ben
