Laurent, I replied to you instead of to the list.
OK, I found the answer on how to set auto exposure off (using
uvcdynctrl), but from as far as I found out, it really depends on the HW
supporting it, and even on the value tto be used.
Anyway, I believe I am missing the basics here. If the webcam is varying
the frame rate, it is still keeping the elapsed time the same as the
wall clock, correct? If I record 10 seconds, it will be 10 seconds,
regardless of the changes in frame rate. Is that correct?
Thanks
Cesar
--- Begin Message ---
Hi Laurent,
No, I did not. Does it depend on the camera model to set a given flag,
or is it universal provided that the camera is uvc compliant? How could
I do it?
Thanks
Cesar
Laurent Pinchart wrote:
Hi Cesar,
On Tuesday 23 February 2010 01:48:10 Cesar Maciel wrote:
Hello,
I am trying to capture from a webcam with a fixed frame rate. I am using
ffmpeg (svn revision 21498) with the following options:
./ffmpeg -y -t 00:01:00 -f video4linux2 -r 30 -s 352x288 -i
/dev/video0 -vcodec msmpeg4v2 -f avi -r 30 video.avi
I used two webcams where uvcvideo shows being capable of 352x288 at
30fps. For some reason, ffmpeg cannot keep the input frame rate, and it
starts to go down. There are processing resources available in the
system (Ubuntu Karmic 9.10, and also Voyage Linux 0.62 (Debian-based). I
have tried specifying the qscale option, but it did not make any
difference. Also, both cameras can output raw and mjpeg, but it also did
not make a difference.
Have you tried disabling auto-exposure ? Most cameras adjust the frame rate
based on lightning conditions.
I have updated uvc on Karmic to the version available as a gzip file on
the official website. dmesg shows tons of
uvcvideo: Dropping payload (out of sync).
and every now and then:
[28339.492016] uvcvideo: uvc_v4l2_ioctl(VIDIOC_QBUF)
[28339.492022] uvcvideo: Queuing buffer 30.
[28339.492030] uvcvideo: uvc_v4l2_ioctl(VIDIOC_DQBUF)
for both cameras. On Voyage Linux (kernel 2.6.30), it shows several msgs
like the following ones
[26440.191029] uvcvideo: Queuing buffer 3.
[26440.191405] uvcvideo: uvc_v4l2_ioctl(VIDIOC_DQBUF)
[26440.201496] uvcvideo: uvc_v4l2_ioctl(VIDIOC_DQBUF)
[26440.211579] uvcvideo: uvc_v4l2_ioctl(VIDIOC_DQBUF)
[26440.221661] uvcvideo: uvc_v4l2_ioctl(VIDIOC_DQBUF)
[26440.230034] uvcvideo: Frame complete (EOF found).
[26440.231743] uvcvideo: uvc_v4l2_ioctl(VIDIOC_DQBUF)
[26440.231753] uvcvideo: Dequeuing buffer 4 (3, 14800 bytes).
[26440.249905] uvcvideo: uvc_v4l2_ioctl(VIDIOC_QBUF)
[26440.249921] uvcvideo: Queuing buffer 4.
[26440.249950] uvcvideo: uvc_v4l2_ioctl(VIDIOC_DQBUF)
Cameras are Microsoft NX-3000 and Genius eFace 1325R
Does anyone have an idea, or need more info?
--- End Message ---
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