[raffriff42]

FFMpeg: How to speed up / slow down a video

Using a complex filtergraph, you can speed up [or slow down] video and audio at the same time:

ffmpeg -i input.mkv -filter_complex "[0:v]setpts=0.5*PTS[v];[0:a]atempo=2.0[a]" -map "[v]" -map "[a]" output.mkv

Avisynth is another option, handy for fixing all sorts of things like this, on the fly (you play the script directly, without re-encoding)

DirectShowSource("input.mkv")
AssumeFPS(5, sync_audio=true)