How to speed up video to make timelapse?

Question

I've got a video file with 1.0 FPS (i.e. one frame per second) and would like to re-encode it so that it plays ca 20x faster.

A short 1 FPS sample is here: http://s3.aws.nz/cam-1537668742.mp4

I can play it 20x faster using mplayer like this:

mplayer -speed 20 cam-1537668742.mp4

How can I save it as a video file at this speed?

I tried ffmpeg's setpts filter, it made the playback faster but still at 1 FPS, i.e. it the picture changed only every one second even though more time has lapsed in the meantime.

Any idea? Either using mplayer, ffmpeg or some other Linux tool?

Thanks!

Answer 1

Basic template is

ffmpeg -i in -vf "setpts=(PTS-STARTPTS)/20,fps=20" out

or

ffmpeg -i in -vf "setpts=(PTS-STARTPTS)/20" -r 20 out

Without the fps filter or -r option, ffmpeg will assume the framerate of the output stream is still 1 fps and so will drop 19 out of each 20 retimed frames.