The command pcastaction is a tool included in Snow Leopard to manipulate QuickTime and MPEG movies in a lot of ways: trim, append, extract soundtrack, watermark, and so forth.
The command is used by Podcast Capture to handle video to send to a MacOSX Server (Podcast Producer) but can also be used standalone. It is written in Ruby and uses Apple QTKit.
A few preliminary notes:
pcastaction qtinfo --prb=`pwd` --input=`pwd`/movie.mp4 pcastaction qtinfo --prb=/Users/john/Movies/ --input=/Users/john/Movies/movie.mp4
pcastaction extracttracks --prb=`pwd` --input=`pwd`/movie.mp4 --output=`pwd`/movieaudio.m4a --type=audio
pcastaction extracttracks --prb=`pwd` --input=`pwd`/movie.mp4 --output=`pwd`/movie.m4v --type=video
pcastaction addtracks --prb=`pwd` --tracks=`pwd`/movieaudio.m4a --input=`pwd`/movie.m4v --output=`pwd`/movie_av.mp4
pcastaction getposterimage --prb=`pwd` --input=`pwd`/movie.mp4 --output=`pwd`/movie_pic.png --time=120.20
pcastaction trim --prb=`pwd` --input=`pwd`/movie.mp4 --output=`pwd`/movie_trimmed.mp4 --start_time=10.10 --end_time=1250.30
pcastaction join --prb=`pwd` --input1=`pwd`/movie1.mp4 --input2=`pwd`/movie2.mp4 --output=`pwd`/movie_joined.mp4
pcastaction flatten --prb=`pwd` --input=`pwd`/movie_av.mov --output=`pwd`/movie_av_flatten.mov
Mac OS X Hints
http://hints.macworld.com/article.php?story=20110325095903592