I convert for the PSP and am trying to determine what the differences are between AVC/H264 & MPEG4 and would appreciate any feedback from the community. I have tried both at the default quality of 15 for AVC/H264 and 23 for MPEG4. While the video appeared similar, I think the MPEG4 was a little better. However the AVC/H264 file was 35% smaller but over twice as long to convert (Just ripped Thin Red Line 2:50 movie - 3:45 to convert AVC/H264 at 15 quality - 1:13 to convert MPEG4 at 23 quality ). Has anyone experimented with the two format? Any experiences out there? What quality level looks best? Is there a difference on sound? If file size is the only good thing, I don't know that it is worth the extra time.