Can you add
PSPEnc (one of my personal favorites, though it won't do mp4 to mp4 and I still don't know how to make it put in mkv subtitles, though I know it did at some point)
jonny's Homepage
also I would just like to say that the PSP Video Express player you recommended is amazing. it doesn't allow much control over the video resolution or much else, but it does just what I needed which is to convert a mkv file and keep the subtitles. thanks a ton.
one last thing. Psp Video conterter is also amazing. it uses my CPU to the fullest and takes the full amount of time that it takes to play the video to encode it. However the quality is amazing and the video file size is just for freaking small I had no clue it could be so small and yet so good. it made a video at 482x272 resolution come out as like 86 MB and it looked better than the 192 MB file I had from another program.