[FFmpeg-user] Change frame rate without dropping/adding frames

[Nicholas Robbins]

> On Thursday, January 15, 2015 7:30 PM, Elliott Balsley <elliottbalsley at gmail.com> wrote:

> > After a long break from this issue, I have a new problem.  For
> example, I want to take a 24fps video and make it play slow-mo at
> 12fps.  The input option -r is dropping frames, rather than slowing
> down the playback speed.  I don't have my main computer right now,
> which uses the latest git master; I'm just using my laptop which uses
> a macports build, so maybe that's the reason?  Or am I using this
> command wrong?
> 
> $ ffmpeg -r 24 -i /temp/leader.mp4 -r 12 test.mov


You are using the command wrong. That says "use this input as if it were 24fps. Do stuff with that, and then encode the resulting video as 12fps, discarding/dupping frames if needed."

Two options that should work:

ffmpeg -r 12 -i /temp/leader.mp4 test.mov

or

ffmpeg -i /temp/leader.mp4  -vf setpts=2.0*PTS test.mov

-Nick