[FFmpeg-user] Increase video speed via framerate change?

[Tom Evans]

On Wed, Oct 30, 2013 at 12:20 PM, Richard llom <richard.llom at gmail.com> wrote:
> Hello,
> I have an video with 4 fps, I want to speed this up (time lapse), but also
> increase the framerate, so I thought:
> ffmpeg -i input.ogv -r 12 output.webm
>
> will do the trick, but no avail. Video is still the same length, how can I
> do this in ffmpeg?
>
> TIA
> richard
>

I gave this advice before in the past:

ffmpeg -i rtsp://... \
-vf "select='not(mod(n,25)),setpts=0.04*PTS" \
-c:v libx264 -an out.ts

This takes a 25 fps video, drops 24 out of every 25 frames, and
re-encodes as a 25 fps video that is 0.04 the length of the original.
For every 25 minutes of source footage, you get 1 minute of time-lapse
footage output.

Read this thread for more info:

http://ffmpeg.org/pipermail/ffmpeg-user/2013-February/013555.html

Cheers

Tom