Compressibility-check

[yosemite]

hi,

could u explain me what that "compressibility-check" excactly is?
Is read something about it and I see it in G-Knot, but I dont understand it ;)

Which things do I need for this check, why is it useful, what effects has it, etc...

That would help me much ;)

thx u!

[Prizm]

Could someone please answer? I'd also like to know what exactly
GK is doing with this 'compressibility check', and how you're
suppose to determine filesize from it.

Prizm

[diji1]

Hi,

The compressability check basically lets you choose an appropriate resolution for the bitrate that the gordian knot calculated for you.
Its too enable you to get higher quality rips and should definitely be used.

When you run it it encodes a portion of the movie - 5% by default - using the settings you chose in the main gui. From this it gives you a figure between 1% - 100% in the Bits(pixel*frame) section in the gui. This is an indication of the quality of the movie. 60%-70% is good quality, above 70% and you cpould probably raise the res ur using. I usually try and aim for 70% when i run the test..... just
lower res to bring the figure up or raise ur res to lower it..... imo opinion it works very well.

Hope this helps... btw, all this is in the guide :|

[Dionysus]

I'm glad I read this thread but now I've got a question. Why would it always crash on me when i try to run the compression test. Everytime I've hit that damn button it brings up a blue screen and then after that Gknot crashes. I hope someone has some sort of explaination for it.

thanx.

[jggimi]

I had blue-screen-of-death with compressability test with 21 and 22. Went away with 23. Platform is WME and AMD Athlon. Compress-check for DivX 4 does very nicely for me now. I put BBC's Walking with Dinosaurs on 2 CDs due to that test; wouldn't have done so without it.

I'm glad that the check is there for DivX 4 -- I feel like re-visiting some of my .avi files again.

[philippas]

When you aim for a value less than 100% you will always reach the filesize. The best is to reach 100% in compressibility test. Then the hall film will be encoded with 2-2 main DRF.
70% is not the perfect aim

Off course i don't tell to go to something like 320x240 resolution to reach the 100%. If you go for a very small resolution you will loose quality, because every resize algo has it's limitations.
70% will give a good balance between resolution and quality.
Myself i prefer to go for 2 cd's and aim very close to the 100%.

[Dionysus]

Okay I have a couple questions on this check. When I'm about to do it what is the percent there suppose to be, it goes from 1 - 15% so I just left it at 5% but what does it do when I change it just so I know for later dates. And the other question is. After it's done doing it's check it gives me these values 77.1% of 0.223 compressibility test and then just above that under the Bits/Pixels*Frames it has turned yellow with a value of 0.172. Can someone tell me what all these values mean and how they change the outcome of my movie.

I've never used the compressing check before on any of my movies cuz I was too lazy to try and figure out why it always crashed on me so now it works and I'm curious as to what they all do. My other movies turned out good so...

Thanx ppl.

[jggimi]

My understanding is a compressibility check is first-pass encoding, of a small portion of the content. Default is 5%. It does what it says it does: examines how compressible the content is.

My understanding is that you can use the test to get a more accurate sizing of your final output, and a more accurate understanding of the quality of the output you'll get at the resolution and bitrate you've currently set.

Again, my limited understanding is that there are basically two knobs you can adjust: Resolution, and Bitrate. You set those, but the codec does the compression. A compression test can let you know, in a few minutes, the apparent quality of the result prior to running the complete job.

theWEF, did I describe it properly?

[philippas]

If you read the docs of GordianKnot you will understand what those settings do.

The percentage in the compressibility frame box mean how much percent of the movie will be encoded for the test.

The bits/(pixel*frame) value is just an indication to which resolution you should choose before you do the compressibility test.
After the compressibility test is done you should ignore the bits/(pixel*frame) "rule" and set the resolution accordingly to the value next to the load button.

The percentage that appears when you load the stats file is the quality indicator i.e. 70%, 90% and it is very accurate.

[OUTPinged_]

ok, to make things clear.

1. compresibility check checks how much the movie will compress.

2. it takes each 13 frames of 240 (5%) and encodes them on 2x drf.

3. first to second pass ratio is an indicator, how much your movie will be compressed DRF wise.

4. "good" quality. "best" quality. thats a bullshit. select your favorite resolution (you are making a rip that youd like, not some smartass on a doom9 webboard, right?) and check if a percentage will be in a 66-75 range(for divx3 encode). if smaller, that rip will suck bigtime and you have to lower a res one notch or go for 2cd lol. if bigger then you are safe to make a better quality sound or up the resolution.

gl people, rtfm and browse the damn webbiard, all of your questions were answered here 9999999times!!

[jggimi]

Per your advice, I've gone back to rtfm again, and here is what I read in Doom9's DivX4 guide about compressability testing:

Values between 40% and 100% mean good quality, below 40% the quality will be inferior so you should compensate by reducing the resolution (you'll see how the value adjusts.. if the field background is white it's ok, if it's yellow it's critical but can still look good and if it's red it will look bad, period). The ideal range is 45% - 55%, above that value you could select a higher resolution. Once the value is in the acceptable range, save the avs again but this time turn off the Compressability Check off.

A word of advice: This compressability check for DivX4 hasn't been as thoroughly tested as the one for DivX4 [sic: DivX3] so the ideal values might not always be in the suggested range. Personally I usually go lower than the lower bound for good quality and the quality is still ok for me. However, 35% should definitely be something like a lower bound not to be crossed.

[X-Calibar]

Originally posted by jggimi
I had blue-screen-of-death with compressability test with 21 and 22. Went away with 23. Yessss! That WAS helpful. I didn't know about an update and didn't see it before... yay :) ty

EDIT: oh hoho! Look 1 post!