ffmpeg commands to create a "drawing" style video

Enhancing local contrast and creating lines

ffmpeg -ss 60 -i film.avi -vf hue=s=0,\
lutyuv="y=2*val",smartblur=1:1:0,edgedetect=low=0.1:high=0.2\
-vcodec huffyuv -pix_fmt bgra -y dessin.avi

To extract an alpha channel

ffmpeg -i  film.avi -vf alphaextract -vcodec huffyuv -y alpha.avi

To merge a alpha channel to an existing movie

ffmpeg -i dessin.avi -vf "movie=alpha.avi[alpha];[in][alpha]alphamerge[out]" -vcodec huffyuv -y dessin2alpha.avi