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Incorrect start times with variable frame rate (VFR) videos #20
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meantime I managed to get the frame rate constant by unchecking 'exposure,auto priority' on my C920, so now I can manage. But the software problem remains. |
Hello I did some more extensive testing and am attatching a small 'problematic' The original movie was recorded using guvcview. It has motion events at 10 The first event is detected correctly by dvr-scan at 9.4 secs. The generated movie This is the command I used to do the detection, plus output: dvr-scan -t 0.001 -i my_video-x7.mkv
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Technically this is working as expected, but this raises a good point of how to deal with variable framerate videos, which are more common on DVRs now a days. I may need to change the approach that DVR-Scan takes to instead rely on Thoughts? I was trying to come up with a "batteries included" approach, but I don't think OpenCV provides a way of outputting VFR videos, so I might not be able to address this without introducing an external dependency on ffmpeg. |
After some thought, the right way to go is definitely through better integration with PySceneDetect and FFMPEG to resolve this, as PySceneDetect also has the same issue (Breakthrough/PySceneDetect#168). Even without VFR support, integration with PySceneDetect should prevent the issue you're seeing with the output video being sped up. Once that integration is complete (planned for v2.0), and the linked issue in PySceneDetect is resolved, DVR-Scan should no longer have any issues with VFR videos. |
Hello
I'm using dvr-scan to find motion start times in webcam movies recorded in guvcview. When I looked up the start times in the movie with mplayer, I noticed the actual events and start times don't match up. I did some testing using different movie formats and cam settings. Sometimes, in low light conditions, the camera's frame rate drops. In these movies, dvr-scan seems to get the start times wrong. I also managed to make a couple of movies with constant frame rate (lot of more or less constant light) here the start times are correct.
Is there some work around for this? In my application I can't be sure the light is always constant. Also the frame rate variability seems to happen irrespective of cam settings (absolute exposure, raw formats ...) What I also tried is re-code the movie with ffmpeg using -r 30. Same bad result...
Jos
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