Peculiarity with VideoWriter codec selection....

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I ran into issues with VideoWriter coding flv, so I found hope by forums claiming I should install all sorts of codecs + FFMPEG manually from source, and rerun cmake + make + make install in opencv 2.4.5 directory. cmake claimed it found all the required FFMPEG dependencies and will use them (However, I did not explicitly tell cmake to do so...).

Then, I attempted:

out.open("/home/dror/Videos/IMG-0.flv", CV_FOURCC('F','L','V','1'), cap.get(CV_CAP_PROP_FPS), S, true);

And it blessed me with:

[flv @ 0x173f7a0] Tag FLV1/0x31564c46 incompatible with output codec id '22' ([2][0][0][0])
OpenCV Error: Unsupported format or combination of formats (Gstreamer Opencv backend doesn't support this codec acutally.) in CvVideoWriter_GStreamer::open, file /home/dror/src/opencv/modules/highgui/src/cap_gstreamer.cpp, line 505
terminate called after throwing an instance of 'cv::Exception'
  what():  /home/dror/src/opencv/modules/highgui/src/cap_gstreamer.cpp:505: error: (-210) Gstreamer Opencv backend doesn't support this codec acutally. in function CvVideoWriter_GStreamer::open

I changed the file extension:

out.open("/home/dror/Videos/IMG-0.avi", CV_FOURCC('F','L','V','1'), cap.get(CV_CAP_PROP_FPS), S, true);

And it worked fine. (If you belive ffmpeg -i output)..

Possible reasons:

1. I didn't EXPLICITLY tell cmake to use FFMPEG.
2. The sources I used don't reside in /usr/src?
3. I should have purged manually OpenCV installation before reinstalling..?
4. I'm using too old a version of FFMPEG..? (ffmpeg-0.11.1)
5. This is a peculiar bug..
6. This is where you come in! :)

Help!