It is possible to make (motion) history videos in both the Matlab and Python versions of the Musical Gestures Toolbox, but today I was curious as to whether it could be done simply with FFmpeg. I was therefore curious to try out making such a grid-based display from a history video, which actually shows some more of the actual motion. It is possible to get some idea about her spatial distribution, but there is little information about her actual motion throughout the sequence. It also shows how the dancer moved around in the space. The 9 frames in the display above reveal that there is little dance in the first one third of the video file (can see the arm of the dancer enter in the third image). Running this script on the original video gives this image: I was therefore happy to find a nice script made by Martin Sikora, which is based on looking up the duration of the file and use this to calculate the frames to export from the file. That is not so easy if the sampling is uneven. From an analysis point of view, it is actually quite useful to know more or less when things happened in the video. The second problem with sampling one “salient” frames, is that we loose information about the temporal unfolding of the video file. This is usually not the case in the videos that I study, which are primarily recorded with a stationary camera in which only the “foreground” changes. First, it requires that there are scene changes in the video. I see that many people create such displays by sampling based on scene changes in the video. I want to include frames that represent the whole video. The problem is that the image only contains information about the 1600 first frames, or more specifically frames 0, 200, 400, 600, 800, 1000, 1200, 1400, 1600.
In the above code it looks up every 200th frame, which gives this image: The problem with this approach, and many similar that I found by googling around, is that it samples frames with a specific interval. It is possible to do it with a one-liner: ffmpeg -ss 00:00:05 -i dance.mp4 -frames 1 -vf "select=not(mod(n\,200)),scale=495:256,tile=3x3" tile.jpg I spent some time exploring different ways of doing this. The first attempt is to create a 3×3 grid image by just sampling frames from the original image.
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