BBC Four often show old programmes (like Doctor Who and Batman) that are transmitted in widescreen, but with black borders down the sides to keep the original 4:3 aspect ratio of the main picture. As the screen on my Archos (and my phone) are 4:3, it seems silly to play the widescreen broadcast in letterbox, and leave the picture in a tiny box in the middle.
So this screen crops the borders off the side, thus converting a widescreen broadcast to a 4:3 DivX.
It also works for things that really are widescreen – when converting for a 4:3 display, it’s sometimes more watchable to have a bigger image with the side of the picture missing, than being able to see the whole picture, smaller.
This does a two pass encode for better quality.
ffmpeg -i inputfile.mpg -vtag DIVX -f avi -vcodec mpeg4 -aspect 4:3 -cropleft 100 -cropright 100 -pass 1 -s 640×480 -b 1000k -acodec mp3 -ab 128000 -ar 48000 -ac 2 outputfile.avi
ffmpeg -i “$f” -vtag DIVX -f avi -vcodec mpeg4 -aspect 4:3 -cropleft 100 -cropright 100 -pass 2 -s 640×480 -b 1000k -acodec mp3 -ab 128000 -ar 48000 -ac 2 outputfile.avi