I'm a real Pd newbie and am currently using a patch created by someone else.
The patch loads .mov videos using the GEM object "pix movie". I've noticed that for some videos the reported number of frames is different than what I see if I open the same video using the Quicktime viewer. Here is what else I know:
The videos made using iMovie load in Pd with the same number of frames as what I see in Quicktime, but the videos made on a Windows machine have consistently fewer frames.
The longer the movie, the greater the discrepancy in the number of frames. This suggests a frame rate issue but all videos were made with the same frame rate.
In short, how does Pd calculate the number of frames when video is loaded?