DVD File Sizes Created After Encoding?

[pglenn]

I have a question in regards to conversion quality and sizes. I have done 2 AVI movie files now using KDVD/ DIKO, each at about 700 megs in size. Now when they converted to DVD format, one was about 1.4gig and the 2nd was 749,894k. I looked at the log file for the 2nd and it said it used 6072 average bitrate. I watched the first 15minutes of the DVD file (using POWERDVD) and the quality seemed good, not too different from the original AVI file, which itself was pretty good.

Now this seems really odd to me. I am used to, on the average, a good quality AVI being 700meg and the corresponding MPG at 5000k bitrate at about 3gig (using TMPGENC or DVD WorkShop encoders). So, why the descrepancy in file sizes here? Is the quality really so bad and I just cant tell? or is it just using routines that are so efficient? or is "average" bitrate that it is using for encoding, that much more efficient with file sizes than "constant"? (I believe but not 100% sure that I have usually used CBR instead of VBR in the past - would that make so much of a difference in file size?)

Patrick

[Prodater64]

If you use CBR, all mpeg file will have bitrate that you selected.
A mpeg file encoded with VBR, will have a average bitrate that you selected, but the encoder will down bitrate if movie scenes don't need it. Also will rise bitrate when needed. Result will be a better mpeg file with better distribution of bitrate. In other words, for same final filesize, better quality for VBR.

[pglenn]

Well that is what I figured as far as quality and bitrates, but would the file size drop to about 1/2 the size using variable as compared to constant?