ffmpeg -i file.mp4 -ss $DUR -i file.mp4 -map 1:v:0 -map 0 -filter:v:0 scale=320:-1,trim=end_frame=1 -c copy -c:v:0 mjpeg -disposition:0 attached_pic out.mp4

ffmpeg -i JoseVega.RATWM.mkv -map 0:v -map -0:V -c copy JoseVega.RATWM.png