I use a lot of clips from movies and TV ads in role as a trainer. Having recently moved over from PC to Mac, I have been searching for a combination of Apps that will allow me to extract clips and covert them to mp4. I can recommend the above combination mac the ripper and squared 5.
Both available as freeware and freely downloadable.
You will also need to pay for and download MPEG-2 software from Apple at £15.