The DVD commentary track is a must for a film buff who wants to either learn camera angles and SFX
or just wants some behind the scenes tidbits and finished off the special fatures earlier. It's activated by rooting through the menus or changing the audio track with a remote control for the DVD player. Some tracks are director, others include the main actors, some have the SFX experts. The Fight Club
DVD itself has 5 commentary tracks, I believe; The Director, The Director and actors, the Author and scriptwriter, the sfx people, and the people in charge of photography.
These tracks are recorded by people watching the film in a room, with microphones and headphones on. Nowadays, sometimes they will take commentary from two actors and splice them together from different times. The problem with that is you get the feeling one keeps cutting the other off.
While most of the commentary tracks are just audio only, there are exceptions:
Ghostbusters: with Ivan Reitman, Harold Ramis & Joe Medjuck is the first DVD to use MST3K-style silhouettes of the people talking and looking up at the movie, maybe even pointing. All we can hope for is that more DVDs come this way.
Mallrats, made by Kevin Smith, has the special ability to see most of the cast discussing the movie in the corner of the screen, while they're watching the movie, as well as the audio. One of the rare DVDs to use the multiple-angle viewing in the DVD player.