Inspired by stuff like this, I thought it would be fun to make color bars representing Chunky Milk's movies. The average color in each frame is taken and put on a left-to-right timeline.
I made these images thusly:
ffmpeg -i movie.mp4 -s 1x1 -c:v png pixel/%06d.png ffmpeg -i pixel/%06d.png -filter_complex tile=1000x12 line.png
...And then doing some fairly straightforward stitching/stretching in GIMP.
Stock ffmpeg won't make tile mosaics (even 1x1 pixel ones) more than 1024 tiles wide or tall, so I had it generate, in the example above, 12 lines of 1000 pixels each. That's what I stitched together in GIMP. For longer films (not mine :^) I've done a custom build of ffmpeg increasing the define for REASONABLE_SIZE in vf_tile.c, but for these shorts, this was automated enough.
I also made some "slice" versions, taking the average color of each horizontal line of each frame and doing the same thing. There's enough detail to see vertical motion including zooms, panning, and credits rolling.
I made these images the same as above, except scaling to 1x128 instead of 1x1:
ffmpeg -i movie.mp4 -s 1x128 -c:v png slice/%06d.png
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