I am using v4l programing for my v4l frame capture
card. and now I can use mmap capture to get my video .
it seems ok. But now I encounter a problem---how can I
change my capture size without close v4l card ?
The following is my code of changing size ,but it does
work . I dont know why.
set_size(int width,int height)
{
gb_frame = 0;
/* start to grab the first frame */
gb_buf.frame = 1 - gb_frame;
gb_buf.height = height;
gb_buf.width = width;
gb_buf.format = VIDEO_PALETTE_YUV420P;
ret = ioctl(video_fd, VIDIOCMCAPTURE, &gb_buf);
if (ret < 0 && errno != EAGAIN) {
/* try YUV422 */
gb_buf.format = VIDEO_PALETTE_YUV422;
ret = ioctl(video_fd, VIDIOCMCAPTURE, &gb_buf);
if (ret < 0 && errno != EAGAIN) {
/* try RGB24 */
gb_buf.format = VIDEO_PALETTE_RGB24;
ret = ioctl(video_fd, VIDIOCMCAPTURE,
&gb_buf);
}
}
if (ret < 0) {
if (errno != EAGAIN) {
fprintf(stderr, "Fatal: grab device does not
support suitable format\n");
} else {
fprintf(stderr,"Fatal: grab device
does not receive any video signal\n");
}
return 1;
}
return 0;
}
this function always return 1;ie ,it cannot
successfully exec ioctl functions.
but in my open code , this part is also include in it
. it never fails. why this happen ? what lead to it ?
please give your help .
thanks in advance .
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