[FFmpeg-user] Way to encode and crop dynamically by keyboard

[David Barbassat]

Dear All, 

I am looking for a way to encode by ffmpeg a video but with a dynamic
crop provided by shell variables 

For example is it possible to use ${x} and ${y} in the command line and
change them during the encoding process without launch the encoding each
time ? 

Like a crop motion :) 

Regards 

David