Re: Video4linux

["Peter Teoh" <htmldeveloper@xxxxxxxxx>]

On Sat, Jan 3, 2009 at 1:52 AM, niamathullah sharief
<shariefbe@xxxxxxxxxxx> wrote:
> Hello
>
> I am looking for a very basic "c" example that will connect to a V4L2 webcam
> and capture a frame. I am basically looking to write a class which I can use
> to create a new Webcam object. which will grab a frame from the camera,....

for a start, u should search for a userspace C program that can read
from webcam object, try:

1.   www.google.com/codesearch

2.   www.sourceforge.net

and enter "webcam".

for example, from codesearch I found the following fragments:

http://www.google.com/codesearch/p?hl=en#3g4bv2F2LZQ/xvcam/xvcam.c&q=webcam%20drivers

init()
{
   struct video_capability grab_cap;
   struct video_channel grab_chan;
   struct video_mbuf vid_mbuf;

   atexit(deinit);

   if ((grab_fd = open("/dev/video0", O_RDWR)) == -1) {
      fprintf(stderr, "Couldn't open /dev/video0: %s\n", strerror(errno));
      exit(-1);
   }

   if (ioctl(grab_fd, VIDIOCGCAP, &grab_cap) == -1) {
      perror("ioctl VIDIOCGCAP");
      exit(-1);
   }

   grab_chan.channel = 0;

   if (ioctl(grab_fd, VIDIOCGCHAN, &grab_chan) == -1) {
      perror("ioctl VIDOCGCHAN");
      exit(-1);
   }

   grab_chan.norm = 0;

   if (ioctl(grab_fd, VIDIOCSCHAN, &grab_chan) == -1) {
      perror("ioctl VIDIOCSCHAN");
      exit(-1);
   }

   grab_buf.format = VIDEO_PALETTE_YUV420P;
   grab_buf.frame = 0;
   grab_buf.width = yuv_width;
   grab_buf.height = yuv_height;

   ioctl(grab_fd, VIDIOCGMBUF, &vid_mbuf);

   grab_size = vid_mbuf.size;
   grab_data_tmp =
       mmap(0, grab_size, PROT_READ | PROT_WRITE, MAP_SHARED, grab_fd, 0);

   if ((grab_data_tmp == NULL) || (-1 == (int) grab_data_tmp)) {
      fprintf(stderr, "Couldn't mmap\n");
      exit(1);
   }

   /* Useless? probably. */
   setpriority(PRIO_PROCESS, 0, 20);
   nice(20);
}


-- 
Regards,
Peter Teoh

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