uvc_v4l2_try_format
ret = uvc_v4l2_try_format(stream, fmt, &probe, &format, &frame);
return uvc_v4l2_try_format(stream, fmt, &probe, NULL, NULL);
ret = uvc_v4l2_try_format(file, fh, fmt);
.vidioc_try_fmt_vid_out = uvc_v4l2_try_format,