OT: How to convert ___ files to ___ files.

[ScarySquirrel]

Post two lines here with any command line or Xt7 ways that fellow users could try to convert one file type to another.
We all have knowledge of one sort or another. Post here and share the wealth!
For instance:

mp3 to flv
mencoder infile.mov -o outfile.flv -ofps 15 -of lavf -oac mp3lame -lameopts