If you're having trouble syncing your audio commentary to a DVD, view this related Knowledgebase article. (Quick tip: if your commentary is running faster than the movie, you're probably listening to the PAL format instead of the NTSC. Switch to the NTSC format instead.)
NTSC and PAL are "region codes" used by broadcasters as required around the world. In these cases, NTSC (also known as Region 1) is mostly used in North America, including Canada and the United States, while the PAL (Region 2, for example) is used in other countries.
These formats describe technical data about the video that is using that region code; for example, NTSC runs at a frame rate 24 fps, while PAL runs at a slightly higher 30 fps. There are other subtle differences between the two, but we only care about the frame rate. Since a PAL frame rate is higher than the NTSC counterpart, if you were playing an NTSC and a PAL version of the same movie side-by-side, the PAL version would appear to run just a hair faster than the NTSC version. By the end of the movie, the PAL movie may have ended several minutes earlier than the NTSC version.
Since RiffTrax is a U.S.-based company, we record our commentary tracks to the NTSC version of each movie, and typically we use the most widely available edition at that. In addition, since we do not have access to non-Region 1 hardware, we are unable to completely test our PAL versions which are made by adjusting the playback speed to match the PAL specification.
Luckily for everyone, the advent of Blu-ray and online streaming video have made this situation easier to handle. If you are watching the Blu-ray or stream of your movie, use the NTSC MP3 file we have provided, as this is the version most likely to sync up correctly.
For even more detailed information on regional broadcast specs and their codes, see this article on Wikipedia.