[FFmpeg-user] Treating video frame-based instead of time-based

[Gyan]

On 21-01-2019 02:01 PM, Wolfgang Hugemann wrote:
> Concretely:
> * Could I (easily) extract every nth frame from a video (in order to
> dump the result as JPEGs)?
> * Could I subtract each frame from its predecessor (in order to detect
> minimal motion)?

As Carl mentioned, the select filter with an appropriate expression will 
do this e.g.  select='not(mod(n-1,5))' to select every 5th frame. Frame 
count begins with 0.

There is a freezedetect filter in git master that can detect if a frame 
has changed minimally with respect to the previous frame. Docs at 
https://ffmpeg.org/ffmpeg-filters.html#freezedetect

Gyan