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videoffmpegimagemagickpngalpha

how to batch combine two sequence of images with an alpha channel using ffmpeg or imagemagick?

Other tools or Simple APIs are also welcome.

I have a sequence of pngs with alpha that I want to overlay on top of a few videos. Using ffmpeg would be fantastic, but using imagemagick is also acceptable. I could extract all the frames in the video and use imagemagick to batch blend every frame then re-encode (re-encoding is acceptable).

Solution

  • ffmpeg example. You mentioned "two sequences" so this example assumes you have two sets of sequentially numbered images:

    ffmpeg -i input.mp4 -framerate 25 -i blue_%04d.png -framerate 25 -i red_%04d.png -filter_complex "[0][1]overlay=10:10:format=auto[bg];[bg][2]overlay=W-w-10:10:format=auto[v]" -map "[v]" -map 0:a? -c:a copy output.mp4

    enter image description here
    Example of overlay placements.

    • The first image sequence ("blue") will be placed in the top left with 10px padding and the second ("red") in the top right. If you want bottom left: 10:H-h-10. If you want bottom right: W-w-10:H-h-10.

    • The images in this example are named blue_0001.png, blue_0002.png, blue_0003.png, etc. The pattern is the same for the "red" sequence.

    • See the image file demuxer and overlay filter for more info.