I have a time lapse video with 29.97003 FPS. There is no audio. The video is too fast. I would like to lengthen it from 10 seconds to 20 seconds, while keeping each frame with like 15 FPS.
How can I do that with FFMPEG?
It is short and small in file size. Can be reencoded, I don't care. I'm thinking, if there is no quick solution, I could extract frames to JPG files and encode a new video with different FPS. I'm trying to avoid that.
Edit: I tried this: https://stackoverflow.com/a/45465730/1442225
ffmpeg -y -i input.mp4 -vf \"setpts=2*PTS\" -r 15 -codec:v h264 output.mp4
It looks like it did the right thing. output.mp4 has doubled length but same amount of frames. Only the file size shrank to less than 25% of original. I used the same vcodec. I do expect the file size stay almost the same.