This might be of use for people with PAL DVDs who want to participate in a commentary where everyone else is using the NTSC DVD (or Blu-ray, which runs at the same speed):
MPlayer can be used to reduce the playback speed to NTSC level.
For example, the following would play “Monsters, Inc.” from the Australian DVD (R4) at NTSC speed and pitch on a Mac, with the DVD drive being /dev/rdisk1 and the title number of the main feature being 18:
mplayer -dvd-device /dev/rdisk1 dvd://18 -speed 0.96153846154
On a slow machine video is not exactly smooth, if you do this, but audio sounds fine with no dropouts.
The full documentation for MPlayer can be found here.
Note that not all DVDs work with MPlayer. Most of my Pixar discs do, but “Cars” (German R2) does not.
I have not yet tested Ratatouille and WALL-E.
Recent multicore machines should be able to get smooth video playback.
Just tested this on a Core 2 Duo - video is very smooth now.
For Vista users (if drive E is your DVD drive):
mplayer -vo direct3d -dvd-device E: dvd://18 -speed 0.96153846154
If you assume the NTSC reference source plays at 23.976 fps instead of 24 fps, use 0.95904 instead of 0.96153846154.
Just tested the value of 0.95904 with a PAL DVD of X-Men 2 playing parallel to the Blu-ray version of the same movie, and it worked. So that’s indeed the correct value to use.