Open source developers have focussed a lot of energy on the plumbing. Here are some examples for manipulating file types:

Convert between video formats

ffmpeg -i input.flv output.mpg  

Convert between image formats

convert input.png output.jpeg  

Join together audio files

sox in_1.wav in_2.wav out.wav  

Remove sound from video

mencoder -ovc copy -nosound video.avi -o video_nosound.avi  

Add sound to video

mencoder -ovc copy -audiofile soundtrack.mp3 -oac copy video_nosound.avi -o video_sound.avi