Compressibility test in general

[Shorlex]

Hi everybody!

I tried to find a good thread for my question, but I couldn't, all of these were concrete questions for concrete circumstances.
My GENERAL asking is about compressibility test: what is that? Is it important? Very important, or not so much? (I mean, that I've done a lot of DivX films with about 900 average bitrate, and all of these are in good quality; but I've never used this test; am I stupid?). What rates should I use, if I would like to apply it in the future?
What about film quality and size?
Any other questions, I didn't mention here. : ) Of course: I use 0.35. GKnot.
Thank you for your answere, or for a good link to this theme.

[Axed]

Well, imo compressibility tests are very important. It allows you to size your video properly, keep the resolution at the correct level. Otherwise, you might have problems with high motion, or 'fast' action movies. The most obvious of these problems is macroblocking.

Generally, your better off aiming for a target size, such as 1 or 2 cds, or 1/5th of a dvd, depending how you store your movies. And, two pass encoding will always give you better quality (at lower bitrates) then 1 pass encoding. Check out Doom9's guides for Gordian Knot to see the best way to conduct a compressbility test.

Nutshell version of a compressibility test, make sure your codec settings are exactly what you are going to use (such as qpel, gmc, b-vops and the likes) for the full encode, including your avs file and keep the compressibility percentage at around 70%.

(DivX experts, if that % is wrong, please correct me)