can someone explain to me this 'Bits/(Pixel*Frame)' thing?

[Funkdafied]

I'm a bit of a newbie, and I've been following the guides here to make some divx3 rips.. Most of my rips have looked pretty good..
anyway.. the last movie i did, was a short 83min movie. The bitrate calculator gave me a value of 1004 for a 1cd rip. So I kept going and did the compressibility check.. Now according to the guide, my bits/pixel value should be close to 0.2 for a 1CD rip.. but 0.212 was a mere 44% of the compressibility check! So i lowered the res till I got a value of 0.27 or something, and it came to about 60%.. I made the rip and it came out looking quite nice.. So here are my questions..:confused:
What exactly am I changing with the Bits/(Pixel*Frame) value?
Whats wrong with what I did? Why does it have to be so close to 0.2?

thanks :)
p.s. sorry if something like this has come up before... I did a brief search and didnt come across anything.

[manono]

Hi-

The Bits/(Pixel*Frame) is just a guideline or starting point. I've made good movies with it showing only .14, and lousy ones with .30. It depends on the source material you're working with. So your best bet for getting an idea of how the movie will turn out before actually encoding it is to do the compressibility test.

I'm not sure I answered your questions though.

[grug2k]

Basically, the Bits/(Pixel*Frame) is just a rough indication of the suitability of your target bitrate. If you have 0.100, then you're not going to have a very good looking result.

The compressability check also gives you a good indication, but only does 5% (or whatever) of your movie...if your movie is not consistent in its compressability and it gives you some ridiculously low or high value, then you should also try using the 'general' b/p*f value as your guide.

For the majority of movies, however, you'll want to stick around 0.2.