[Elphel-support] issues with OpenCV

[jeff witz]

Hello Sebastian,

OpenCV hasn't good methods to handle rtp and http flux for now.
We already try all the backend and we finally succeed in getting picture in
compiling the gstreamer form scratch without ffmpeg support.
The problem is that the only way to deal with url, is the module uriscr,
which didn't allow any set-up. So once we get a picture it was with 3 sec.
of delay, which was unacceptable for our realtime purposes.

Furthermore, I see that the connection to the camera is quite long and it
can be a problem for our purpose. So we finally choose to convert the camera
stream to a virtual device using v4l2loopBack plugin. As we had some
stability issues with gstreamer, we decide to use the mencoder backend,
which is much more stable.
Depending of the kernel version One can have simultaneous access the virtual
device. So in order to be sure that we can treat the datas and save the
movies we have avticated the multicast option, then we can now work with
OpenCV, with the classical example given for a webcam.
The other issue we have to solve came from the fact that OpenCV hadn't been
designed for big picture at an high framerate. So we had to remove every
windows that come from OpenCV to use Qt which have better performances.
Finally we achieve our realtime process of picture at any framerate. We
succeed in the treatment of 700 FPS.
If you are interested in such methods, you can send me private mail and I
can guide you. But I don't give any help on the windows platform.
Everything work well with an ubuntu LTS, so there is no difficulties to use
it in this particular context.

Best regards




>Message: 2
>Date: Tue, 15 Mar 2011 16:23:46 +0100
>From: "Schuster, Sebastian" <Sebastian.Schuster at kmweg.de>
>To: <support-list at support.elphel.com>
>Subject: [Elphel-support] issues with OpenCV
>Message-ID:
>     <A54007A6D3ADA94CBD674D9FE82B13CF05C35A59 at MU00EXV01.kmweg.wtlsh.de>
>Content-Type: text/plain; charset="iso-8859-1"
>
>Hello,
>
>I try to open a stream to the camera in OpenCV (Windows OS). OpenCV throws
these error messages:
>>>>>>>>>>>>
[>rtsp @ 0xbefd80]Estimating duration from bitrate, this may be inaccurate
>picture size invalid (0x0)
>Last message repeated 1 times
>[rtsp @ 0xbf2480]Estimating duration from bitrate, this may be inaccurate
><<<<<<<<<<<
>So I have experienced the same issues with the FFMPEG like in this example
<http://wiki.elphel.com/index.php?title=Talk:OpenCV>
>Unfortunately it was not possible for us to rebuild the Windows version of
OpenCV with GStreamer instead of FFMPEG.
>Could you give us some advice for establishing the stream?
>
>Thanks,
>Sebastian




-- 
Jean-François WITZ
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