Hi Basil,
On Monday 15 March 2010 16:09:49 Basil Mohamed Gohar wrote:
> On 03/15/2010 05:40 AM, Laurent Pinchart wrote:
> > On Saturday 13 March 2010 02:55:47 Basil Mohamed Gohar wrote:
> >> I originally posted this to the video4linux mailing list, but I've since
> >> discovered that this is the appropriate place (or so I understand) for
> >> video4linux questions. My question is how can I capture the raw JPEG
> >> image stream (e.g., MJPEG) from my webcam, which reports through v4l2
> >> that it is capable of. I am using the gst-launch cli to gstreamer,
> >>
> >> which confirms that my webcam has this capability:
> >>> image/jpeg, width=(int)640, height=(int)480, framerate=(fraction){
> >>> 30/1, 25/1, 20/1, 15/1, 10/1, 5/1 }
> >>
> >> And, indeed, I can capture using this capability, but the framerate is
> >> not at the specified rate, but at a much lower value (half or less).
> >> So, even if I specify 30fps, I get something less. I can capture the
> >> full 30fps when I use one of the yuv modes, though, so it's clearly
> >> capable of delivering that framerate.
> >>
> >> My webcam is a Logitech QuickCam Pro 5000. The lsusb output is:
> >>> 046d:08ce Logitech, Inc. QuickCam Pro 5000
> >>
> >> An example command line I try is as follows:
> >>> gst-launch-0.10 v4l2src device=/dev/video0 ! 'image/jpeg, width=640,
> >>> height=480, framerate=30/1' ! jpegdec ! xvimagesink
> >
> > Have you tried disabling auto-exposure ? The camera is allowed to reduce
> > the frame rate in low-light conditions if auto-exposure is turned on.
>
> Thanks for replying. I haven't actually tried this yet (I am currently
> at work), but I do not think this is the issue, because when I choose
> the YUV-style modes, I can capture at the full framerates. It's only
> when I select the image/jpeg mode that I get the lower framerates,
> despite explicitly requesting the higher ones.
>
> I suppose it's not impossible that the camera is opting for different
> behavior depending on the mode of the request, but I think that is not
> likely the case. I do appreciate the suggestion, though, and I'll try
> it when I get home.
It could, but that indeed seems unlikely. The USB descriptors advertise 30fps
in MJPEG mode. Unless the information is wrong (in which case this would be a
firmware bug), 30fps should be achievable.
> Meanwhile, does anyone else have any other ideas?
--
Regards,
Laurent Pinchart
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