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Re: [Bino-list] Possible to use two v4l2 inputs?

From: Martin Lambers
Subject: Re: [Bino-list] Possible to use two v4l2 inputs?
Date: Tue, 1 May 2012 09:47:59 +0200

Hi Goetz!

On Mon, 30 Apr 2012 10:29:17 -0600, Goetz Dapp wrote:
> Hi Martin and others,
> On 04/08/2012 01:53 PM, Martin Lambers wrote:
> > Hi Götz!
> >
> > On Sun, 08 Apr 2012 13:30:49 -0600, Götz Dapp wrote:
> >>> The latest version now has an option --device-format to request
> >>> MJPEG format, and the GUI "Open device" dialog was improved to
> >>> allow opening two devices and requesting MJPEG format.
> >>>
> >>> Can you test this?
> >> just tested it, it works just fine! Thanks so much!
> > Thanks for testing!
> >> Just out of curiosity: is there any way to record the bino output
> >> stream?
> > No, currently everything in Bino assumes that media is read-only.
> > Adding encoding support would require serious work and would add
> > *lots* of complexity. I'd rather keep things simple and keep Bino a
> > video player only. Encoding/transcoding of stereoscopic video is
> > probably best left to a dedicated tool.
> >
> > Best regards,
> > Martin
> I have a question regarding ffmpeg - realize this is not an ffmpeg
> mailing list, and apologize in advance. But given your expertise you
> might be able to give me a quick hint how to resolve it, particularly
> since you managed to convince ffmpeg in Bino to capture in MJPEG
> somehow (which the camera natively supports). Since Bino does not do
> "capture," I have been trying to directly capture a stream, but
> failed miserably - and I have not been able to figure out where I am
> going wrong.
> Essentially I am trying to record a stream from a webcam in the size
> 1280x720 at 30fps directly in MJPEG without any conversion.
> Could you give me a hint how to write me a quick command line command
> that does that? Maybe with an visual output, too? I.e. it writes it to
> the file but also displays what it is recording? If that does not
> work, just writing the file would suffice, too.
> I have tried the following command, but only get garbled stuff...
> ffmpeg -an -f video4linux2 -s 1280x720 -b 2000k -r 30 -i /dev/video0
> -vcodec mjpeg /test.avi
> I apologize for my lack of understanding and thank you all in advance,

The way I did this in Bino is to use a 'private option' for the v4l2
device. You can see the supported private options with 'ffmpeg --help';
look for "V4L2 indev AVOptions". It seems you should try '-input_format
mjpeg' instead of '-vcodec mjpeg'. You can also request framerate and
frame size using these private options.

So the following might work:

ffmpeg -f video4linux2 -framerate 25 -video_size 640x480
-input_format mjpeg -i /dev/video0 /tmp/test.avi


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