ffmpeg is a great command line tool for converting between video and audio formats. But good examples are hard to find.

(more ffmpeg examples on my site www.smallsoftware.co.uk)

My main use of ffmpeg is for converting MPEG2 files (typically recorded from DVB-T/Freeview) either into DivX (to play on an Archos portable video player), or lower bitrate MPEG2. When I was learning to use it, I was constantly frustrated by the lack of good examples for commonly used video format. If you're looking for something similar, hopefully this will be useful to you.

Convert to DivX

This creates a DivX file, 4:3 aspect ratio, 320x240 resolution, bit rate of 690k for video, 128k for audio. The right sort of size for my Archos AV420 player.

ffmpeg -i inputfile.mpg   -vtag DIVX -f avi -vcodec mpeg4 

     -aspect 4:3 -s 320x240  -b 690000 -acodec mp3 

     -ab 128000 -ar 48000 -ac 2  outputfile.avi

and the same thing for 16:9 ratio.

ffmpeg -i inputfile.mpg   -vtag DIVX -f avi -vcodec mpeg4 

     -aspect 16:9 -s 320x192 -b 690000 -acodec mp3 

     -ab 128000 -ar 48000 -ac 2  outputfile.avi

Convert lower-rate MPEG2

I've got a Netgem iPlayer in the kitchen for the children to watch cartoons on. Cartoons don't need a very high bitrate (and the children are too small to care about a bit of pixellation anyway), so I lower the bitrate to save disk space (I've still got more than 200Gb of cartoons though...).

This will lower the bitrate to 1536k... that's equivalent to about 5 hours on a single layer DVD. At that low a rate, it's best to take a little longer doing the encoding, so I do two passes.

ffmpeg -i inputfile.mpg -vcodec  mpeg2video -b 1536000 

     -ab 128000 -ar 48000 -ac 2 -pass 1 outputfile.mpg 

rm outputfile.mpg 

ffmpeg -i inputfile.mpg -vcodec  mpeg2video -b 1536000 

     -ab 128000 -ar 48000 -ac 2 -pass 2 outputfile.mpg