File size reduced after ISO conversion?



I have recently converted an avi movie using avi2dvd. Before the conversion, the file was just over 1GB. I added subtitles, a simple menu and encoded it using CCE (the best quality).
However when the ISO image was created it only measured 921MB??
I am currenlty burning the file to DVD disc to check the quality is ok, but this sounds really odd to me?

Any ideas why the file is smaller?


I think I know why the size is reduced, althought I do not know the reason for it…