sizes of MPEG-2 files

[gordon_fan_24]

ok, I've never had this happen before, i have a 4.2GB MPEG-2 file that I want to burn to DVD, the file is in the yellow section (first, does that mean that it will fit, I know that red means that it won't, but what does yellow mean. ) I want to cut off the final minute and a half, to make it the right length, but when i set the out point where I want it (1h 30 min) it actually adds about 0.5GB to the size, why is this happening, and what can I do to fix this.