ffmpegX producing below specified file size

[Beerad]

I have been using ffmpegX to encode dvds to avi files( xvid). I followed the directions on the website to the T but every file is way under what I specified in the calculator (900-1100MB). I'm trying to produce file sizes of 1500MB with AC3 5.1. I have also tried using other bitrate calculators and manually put in the biterate with no success. More then one video_ts files have been tried with the same resulting file size. Any help would be great.

Thanks

[major]

If the video image size and/or motion complexity is below a certain level, the encoding will use a lower bitrate in order to avoid redundancy and waste of bits. You should increase image size and/or decrease qmin to use efficiently all the bits.