I'm using sorenson squeeze 3.5 to compress my files to mpeg-2, but Encore is still transcoding them again. I've used TMPGenc in the past with avi files and Encore did not need to transcode them. I don't want to use avi files anymore so I'm tryin to figure out how to do this through squeeze with QT files. Here's the settings I'm using in Squeeze:
720 X 480
QT input files
I frame rate 15 (not sure what this is for)
The audio is the problem. MPEG audio is only allowed as a part of the DVD spec on PAL systems, and even then it's an optional codec and may not be supported by all players. Use PCM audio instead, and if possible turn multiplexing off. This will result in separate audio and video files, which is the better way to go.
Also- the "I frame rate" (odd way to put it, usually it's described as GOP length or N frames) is the distance between I frames in the MPEG file. I frames are the "whole" frames, the ones that have no temporal compression applied to them. 15 is average for a DVD, I believe 18 is maximum.