Not using all the bitrate I give it!!

[Vegeta]

I am trying to encode a movie....640x352...about an hour and 58 minutes long, keeping the AC3 soundtrack, 2 CDs or a max of 1400MB, etc...yada yada. I used Gordian Knot to calculate the bitrate and it said like 1726 with the AC3 soundtrack figured in. Well, I cranked it and it didn't use it all, something like 1.29GB after the AC3 was added. I've now managed to bump the bitrate up to 2500 exactly, and it is STILL only coming out to be 1.3GB even, and this is still the total size WITH AC3 soundtrack. I have the min and max quantinizers at default since I barely understand all that, which is 12 for the max, 2 for the min. Encoding quality is at the default 85%. Performance/Quality is Slowest, etc etc etc. Is this basically telling me that the movie, even with a max average of 2500kbit/sec, that it does not NEED the extra space and is simply not using it? If so, I understand and that is all I need to be told, taught, whatever. If there IS a way however of squeezing more bits out of the bitrate, and these bits will HELP the overall quality of the video, please help me in all ways if ya can. For any of ya that take the time to read this, thanks for that and any responses. I'm not a beginner but I'm far from being an expert so any suggestions or help is much appreciated, especially if someone else can be taught something from this too. Thanks!!

[wmansir]

Your right in thinking the problem is the codec is getting max quality, so it doesn't need anymore bits.

You can increase the size by giving it more detail to work with. try switching to bicubic resizing if your using bilinear, or increase the resolution. Of course if your happy with the quality of the video as it is, you could use the extra space for the commentary track (if it has one), subtitles, featurette or what ever you want.

Or you could shoot for 1CD, without loosing too much video quality if you dump the AC3. It sounds like a very compressable movie, but I can understand wanting AC3.