Inaccurate Compressibility Test?

[BluDChyLD]

I was doing a 1 cd rip of titanic (i know it's 3 hours long but im short on cds), and before I encoded it I did a 5% compressibility test to see what the best res to use was.

The best I could get was 90%, and the res was 288x128 with 0.3 aspect ratio error. Seem as it was such a low res I decided to preview a frameserv in windows media player.

The picture was awful and really blocky! I then decided to follow of the guideline of sticking to about 0.20 in Bits/(Pixel*Frame), and got a res of 448x192 and the picture was much better :)

Bottom line, just how accurate are the compressibility tests? Other films i've done using it have been ok but this one was awful... I might just adjust the res according to the film's bitrate in future.

Any help appreciated,
BluDChyLD

[manono]

Hi-
The compressibility test is pretty accurate. You're not looking for 100% or something very high. You're looking for 65-75%, and when trying to put a 3 hour movie on 1 CD, you might have to be satisfied with 50% or so.

As for why the 90% one looked so blocky, I have no idea. Maybe it has to do with the super low bit rate you used when blown up in size. The compressibility test is a much better guide for resolution than Bits/Pixel*Frame.

[jggimi]

You're looking for even lower % if you're using DivX 4. It's in Doom9's guide.

[BluDChyLD]

the end result is pretty poor, i think ill re encode it as a two cd rip later on.

The blairwitch project also gave me a low res on compressibilty test, but i think that makes sense as the film has a grainy and blocky look anyway.
Thanks for the help,
BluDChyLD

P.S - After a compressibility test, what type of percent should I use? I always thought 100 was best, should I aim for about 60-70 instead?

[sierrafoxtrot]

for div3.11 go for 60-80%, div4 anything above 45% should be decent, i think i read somewhere the absolute minimum for div4 is 35%.

[jggimi]

As I said in my last post, you'll find percentages to aim for in Doom9's guides.

In addition, Gknot will color code percentages for you. Red = bad.