[MikeBell]

Originally Posted by raffriff42

FFMpeg: How to speed up / slow down a video

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)

I tried this:

ffmpeg -i source.mp4 -filter_complex "[0:a]atempo=0.5[a]" -map "[a]" outputaudio.m4a

and this... which is a simplified, audio-only, option:

ffmpeg -i out.m4a -filter:a "atempo=0.5" -vn outputaudio.aac

Note: I used 0.5 because 2.0 speeds it up 2x and I want to slow it down 2x.

Result: audio sounds horrible It has that weird metallic sounding echo all over the track. It sounds nothing like what you hear when you slow down to 0.5x with VLC.

I'm still unsure how to proceed...

Originally Posted by StainlessS

Nice one Raff, Archiving your post.

Yesterday, encoded MP4 @ Aspect Ratio 240:1, was a bit of a struggle to re-AR @ 2.40:1

Is there a standard ffmpeg fix for that (there is a special ffmpeg version that re-does AR, somewhere on site).
(I used YAMB + MeGUI, about 6 tries to get correct).

EDIT: Some links on changing AR

http://forum.doom9.org/showthread.php?t=152419
http://forum.videohelp.com/threads/3...out-reencoding
http://forum.videohelp.com/threads/3...ut-re-encoding

Several times I managed to change aspect ratio without re-encoding by doing this:

ffmpeg -i in.mp4 -vcodec copy -acodec copy -aspect 16:9 output.mp4