On 03/16/2010 02:30 AM, John Selbie wrote:
> Hi Basil:
>
> I ran the following command line with my Logitech 5000:
>
> gst-launch-0.10 v4l2src device=/dev/video0 ! 'image/jpeg, width=640,
> height=480, framerate=30/1' ! multifilesink location=frame%.4d.jpg
>
> I let it run for 5 seconds or so and then cancel it. When done I had a bit
> more than 150+ frames on disk. Clearly, I'm getting 30 frames per second.
>
> I ran your command line below and compared with the equivalent command line
> of luvcview. The weird thing is that luvcview shows nice smooth video with
> no blur (jpg was the format). gst-launch at the same configuration just
> "seems" like a slower frame rate. Then I dropped down the frame rate of both
> gst-launch and luvcview to 15fps. gst-launch looked more like 7-8 fps.
> luvcview looked fine. Switching gst-launch to YUV was a noticeable
> improvement.
>
> My guess is jpeg decoding mixed with xvimagesink is the issue. More
> debuging. Switching to YUV or the file renderer produces better results.
> More debugging is needed.
>
> Might be better to move this thread of discussion over to the GStreamer list.
>
John,
Thanks for all your help and giving me some leads. I've come to
basically the same conclusion as you. ds over in #gstreamer advised me
to use sync=false on the xvimagesink element, which allowed it to play
the live, JPEG-encoded video at the full framerate. Also, capturing to
files was not affected at all - can capture to the full 30fps to
individual files or into one file (e.g., an MJPEG AVI file). So, the
problem is pretty-much resolved as far as I'm concerned.
>
>
>> From: laurent.pinch...@ideasonboard.com
>> To: abu_huray...@hidayahonline.org
>> Subject: Re: Capturing raw JPEG stream from webcam
>> Date: Mon, 15 Mar 2010 21:00:05 +0100
>> CC: linux-media@vger.kernel.org
>>
>> 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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>
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