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I have around 1000 frames in *.png format, which are named like frame-0.png, frame-1.png, frame-2.png and so on. I read them and generate a movie by following command :

ffmpeg -f image2 -r 20 -i frame-%00d.png -vcodec mpeg4 -y movie.mp4

Let's say I just want to read frames like frame-0.png,frame-20.png, frame-40.png and make a movie out of it. How can I achieve that ?

One possible way I know, is to make movie from all 1000 frames then generate a new movie by skipping frames from the following command :

ffmpeg -y -i movie.mp4 -filter:v "select='mod(n,20)'" out.mp4

Is there any direct method ?

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The direct way to do this is by using the concat demuxer, where the text file only mentions the selected files. Besides being a hack, you no longer get to use the image2 options. The better way is to combine your present commands.

ffmpeg -framerate 20 -i frame-%d.png -vf "select='not(mod(n,20))'" -c:v mpeg4 -y movie.mp4
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  • This works only if all the frames are present. What If I have only frame-0.png, frame-20.png, frame-40.png available.
    – Grayrigel
    Commented Feb 13, 2017 at 14:34
  • Then, you use the demuxer or pipe the images. To pipe, on Win: cat *.png | ffmpeg -f image2pipe -framerate 1 -i - -r 20 -y out.mp4
    – Gyan
    Commented Feb 13, 2017 at 15:00
  • Command in comment above will also work on Linux & macOS.
    – llogan
    Commented Feb 13, 2017 at 18:13
  • Also, I forgot about image autodetection, so you can likely omit the -f.
    – llogan
    Commented Feb 14, 2017 at 23:47

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