I am using Mediapipe to encode MPEG2, and I'm having the classic syncing problem, but I can't figure out where.

I'm using DV captured via iMovie, which appears to be at 29.97 fps. In mediapipe, I set the frame rate changer to 30000:1001, the ppmtoy4m framerate to 30000:1001, and the mp2enc framerate to 4 (NTSC). But, a 9:28 movie ends up being 9:04. What is going on?