Re: newbie programming help: grabbing image(s) from /dev/video0, example code?

["Daniel Glöckner" <daniel-gl@gmx.net>]

On Sat, Mar 01, 2008 at 09:33:08PM +0000, Elvis Chen wrote:
> We have 2 Hauppauge WInTV PVR-150 installed on a ubuntu 7.10 x86_64 machine.
> They appear to the linux as /dev/video0 and /dev/video1, respectively.

On this card video0 and video1 are for MPEG captures.
Use video32 and video33 for YUV captures.

The only possible YUV format is 4:2:0 with rearranged bytes.
Read Documentation/video4linux/cx2341x/README.hm12.

> My first attempt was to find a small/simple API to access the linux/video device.

No need to find another API, V4L2 is small enough:

#include <linux/videodev2.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <unistd.h>

static unsigned char image[720*480*3/2];

int main()
{
  struct v4l2_format vf;
  int i=1,fd=open("/dev/video32",O_RDWR);
  ioctl(fd,VIDIOC_S_INPUT,&i);
  memset(&vf,0,sizeof(vf));
  vf.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
  vf.fmt.pix.width=720;
  vf.fmt.pix.height=480;
  vf.fmt.pix.pixelformat=V4L2_PIX_FMT_HM12;
  vf.fmt.pix.field=V4L2_FIELD_INTERLACED;
  vf.fmt.pix.bytesperline=vf.fmt.pix.width;
  ioctl(fd,VIDIOC_S_FMT,&vf);
  write(1,image,read(fd,image,sizeof(image)));
  return 0;
}

You may want to insert some error checks :-)
And if you want better performance, use memory mapped I/O.

  Daniel

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