Hi Paulo, Thank you for investigation this. On Tuesday 30 September 2014 13:56:15 Paulo Assis wrote: > Ok, > so I've set a workaround in guvcview, it now uses the length filed if > bytesused is set to zero. > Anyway I think this violates the v4l2 api: > http://linuxtv.org/downloads/v4l-dvb-apis/buffer.html > > bytesused - ..., Drivers must set this field when type refers to an > input stream, ... > > without this value we have no way of knowing the exact frame size for > compressed formats. > > And this was working in uvcvideo up until 3.16, I don't know how many > userspace apps rely on this value, but at least guvcview does, and > it's currently broken for uvcvideo devices in the latest kernels. It took me some time to debug the problem, and I think the problem is actually on guvcview's side. When dequeuing a video buffer, the application requeues it immediately before processing the buffer's contents. The VIDIOC_QBUF ioctl will reset the bytesused field to 0. While you could work around the problem by using a different struct v4l2_buffer instance for the VIDIOC_QBUF call, the V4L2 doesn't allow userspace application to access a queued buffer. You must process the buffer before requeuing it. > 2014-09-30 9:50 GMT+01:00 Paulo Assis <pj.assis@xxxxxxxxx>: > > I referring to the following bug: > > > > https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1362358 > > > > I've run some tests and after increasing verbosity for uvcvideo, I get: > > EOF on empty payload > > > > this seems consistent with the zero size frames returned by the driver. > > After VIDIOC_DQBUF | VIDIOC_QBUF, I get buf.bytesused=0 > > > > Testing with an eye toy 2 (gspca), everything works fine, so this is > > definitly related to uvcvideo. > > This happens on all available formats (YUYV and MJPEG) -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
