Comression test results too low values

[szabie]

Hi All!

Well, jump into the middle:

Every time I run compressibility check I get extremly low values
(eg. 0.072 for XviD @ 704*368)
I don't belive, that dvd movies are so compressible..
I get 100% of "second pass compared to comp. check" eg. @ 455kBit/s average bitrate.
I tried it and the result was hm... far from 100%
I got much better quality @1000kBit/s (of course)

So why doesn't tell me the truth the Comp check??

Thanks
szabie

[jggimi]

Hello, and welcome to the forum.

I can't tell what your values were without seeing a Gknot log, but perhaps you're misreading the results? If so...

The best practice is to only use the bits per pixel value only as a starting resolution prior to your very first compressibility test. From that point forward, ignore the bpp value and instead, look at the percentage returned.

It is that percentage that should be used going forward for all adjustments. The percentage is the expected compressibility .vs the .bpp of the test at 100% quality, and that's why I think you're looking at the wrong number.

If this doesn't point you in the right direction, post a Gknot log.

[szabie]

" but perhaps you're misreading the results? If so..."

--== I am sure there was no misreading ==--


2004.10.27. 17:04:53: Job " 1 - _.avi" started.


Gordian Knot
Encoding Job Data:

Type: EncXvid_First
Container: Audio-Video Interleave (AVI)
Number: 0
Name: 1 - _.avi
Platform: WinXP (5.1.2600).2

Files:
VirtualDubModExe: C:\PROGRA~1\GORDIA~1\VirtualDubMod\VirtualDubMod.exe
NandubExe: C:\PROGRA~1\GORDIA~1\nandub\Nandub.exe
AviFinal: C:\PROGRA~1\GORDIA~1\_.avi
AviMovie: C:\PROGRA~1\GORDIA~1\__Movie.avi
AviCredits: C:\PROGRA~1\GORDIA~1\__Credits.avi
MovieFS: C:\PROGRA~1\GORDIA~1\LastCompCheck.avs
CreditsFS:
Log : D:\Down\Jurrasic.Park.1.DVDR.HUNDUB\proba\JP_proba_5_perc_Xvid_LanczosResize_704x368.stats
Stats:
Ecf :
This is a Compressibility Check:
Resolution: 704 x 368

17:04:53: Audio 1, calc: 36992 kb
17:04:53: Audio 1, disabled, no recalc. - you probably want to add this track later.
17:04:53: Audio 2, calc: 36992 kb
17:04:53: Audio 2, disabled, no recalc. - you probably want to add this track later.

Adding this script to C:\PROGRA~1\GORDIA~1\VirtualDubMod\LastJob.vcf :

// $job "XviD First Pass"
// $input "C:\PROGRA~1\GORDIA~1\LastCompCheck.avs"
// $output "C:\PROGRA~1\GORDIA~1\_.avi"
// $state 0
// $start_time 0 0
// $end_time 0 0
// $script

VirtualDub.Open("C:\\PROGRA~1\\GORDIA~1\\LastCompCheck.avs",0,0);
VirtualDub.video.SetDepth(24,24);
VirtualDub.video.SetMode(1);
VirtualDub.video.SetFrameRate(0,1);
VirtualDub.video.SetIVTC(0,0,-1,0);
VirtualDub.video.SetRange(0,0);
VirtualDub.video.SetCompression(0x64697678,0,10000,0);
VirtualDub.video.SetCompData(3012,"AAAAAHYCAAAfLAoARDpcRG93blxKdXJyYXNpYy5QYXJrLjEuRFZEUi5IVU5EVUJccHJvYmFcSlBfcHJvYmFfNV9wZXJjX1h2aWRfTGFuY3pvc1Jlc2l6ZV83MDR4MzY4LnN0YXRzAAByAG8AYgBhAF8ANQBfAHAAZQByAGMAXwBYAHYAaQBkAF8ATABhAG4AYwB6AG8AcwBSAGUAcwBpAHoAZQBfADcAMAA0AHgAMwA2ADgALgBzAHQAYQB0AHMAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABAAAAyAAAAEFTIEAgTDUAIABMADUAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAADQAAAAAAAAAIERITFRcZGxESExUXGRscFBUWFxgaHB4VFhcYGhweIBYXGBocHiAjFxgaHB4gIyYZGhweICMmKRscHiAjJiktEBESExQVFhcREhMUFRYXGBITFBUWFxgZExQVFhcYGhsUFRYXGRobHBUWFxgaGxweFhcYGhscHh8XGBkbHB4fIQAAAAAAAAAAAAAAAAAAAAAAAAAAAQAAAAIAAACWAAAAZAAAAAEAAAABAAAAAAAAAAQAAAADAAAAAQAAAAEAAAAAAAAAAQAAAAAAAAAAAAAAAAAAAGQAAAD0AQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABAAAABkAAAAZAAAAAEAAAAKAAAAAQAAABQAAAAAAAAAAAAAAAUAAAAFAAAABQAAAAAoCgAAAAAAAQAAAAEAAAAeAAAAAAAAAAIAAAAAAAAABQAAAIAAAAAAAAAABgAAAAEAAAABAAAAAAAAAAAAAAAsAQAAAAAAAAEAAAAfAAAAAQAAAB8AAAABAAAAHwAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAADzAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA");
VirtualDub.video.filters.Clear();
VirtualDub.subset.Delete();
VirtualDub.SaveAVI("C:\\PROGRA~1\\GORDIA~1\\_.avi");
VirtualDub.Close();

// $endjob
//
//--------------------------------------------------
// $done

17:04:53: Started Xvid - First Pass: C:\PROGRA~1\GORDIA~1\LastCompCheck.avs
17:09:59: Finished Xvid - First Pass: Duration: 5 minutes, 5 seconds.
17:09:59: Trying to open Log-file.
17:09:59: Success: Log-file open.
17:09:59: Encoded: 2379 Frames.
17:09:59: Speed: 7.789 Frames per Second.

17:09:59: Done.
17:09:59: Log File = D:\Down\Jurrasic.Park.1.DVDR.HUNDUB\proba\JP_proba_5_perc_Xvid_LanczosResize_704x368.stats
Total Encoding Time: 5 minutes, 6 seconds.
2004.10.27. 17:09:59: Job " 1 - _.avi" finished.
_______________________________________________________________________________________________________________________

[jggimi]

Do you have one from an encoding AFTER the compress test? That will show the bpp values from the test, as well as the ratio you used for your encoding. Which is what I was trying to get to in my reply to your first question. 0.072 is a bpp, not a ratio, and it is the ratio (expressed as a percentage of the compressibility test results) which is the critical value.

[jggimi]

To avoid any possible further confusion, the key value of interest is found in the highlighted box after a compressibility test. Changes to resolution or file size will change this value prior to encoding.

[szabie]

I did yet another comp.check, but I see no bpp values within..

Resulting values in the Bits/(Pixel*Frame) after the test:
hmm..
this time there are good values (except the first one)
Upper left value: 0.072
Lower center: 19.8%
Lower right: 0.363 (-> until this here was the extremely low value)

OK, with these values I can working.
Thanks for your help.
I hope there will be no another confusing result..

szabie

[jggimi]

I hope so, too. The 19.8% figure is produced by GKnot, comparing the bpp of the compressibility test to the bpp of your current resolution and bitrates. e.g.: 0.072 / 0.363 = 0.19834 = 19.834% This is a very low figure, and below best practice, which I understand is commonly in the 60-80% range.

The compression test is a 1-pass, 100% quality test that shows the maximum bitrate achievable, estimated (by default) through encoding 5% of your content (14 frames every 280 frames). This means that at the resolution setting used for the encoding, 0.363 was the maximum bpp value achievable.

It's important enough to reiterate this once more, since you don't seem clear on it:The starting value given in Doom9's guides for bpp values is a recommended starting point before the first compressibility test. After that, only pay attention to the percentage value, not the bpp.Doom9 says in both his DivX and XviD guides:The compressibility check gives you a rough indication of how good a movie can be compressed. The 3 values shown above are related as follows: the 0.831 is the value that the compressibility check returned. If the Bits/(Pixel*Frame) value right above the Load button matches this value you have perfect quality, going for a higher value (= a lower resolution) would be overkill as the movie wouldn't look any better.. The limit of the codec has been reached. The 23.7 mean that with the given resolution, your movie will have a 100 - 23.7 = 76.3 % lower Bits/(Pixel*Frame) value than an ideal quality movie (note that ideal quality doesn't mean as good as the DVD.. it means as good as the selected codec allows). The percentage field is marked in red because the value is rather low and GKnot means to suggest that you should lower the resolution for a better result. A percentage value (as displayed) in the range of 40-60% should yield optimal results, a value above 80% is serious overkill. Note that features like B-frames will actually permit a lower Bits/(Pixel*Frame) value and the movie will still look good, so you should take those values with a grain of salt (I happen to know that the movie in question will still look OK with the settings chosen).

You can increase the Bits/(Pixel*Frame) value by decreasing the resolution.

[szabie]

Yes, I know what does the first (upper left) value mean. Just a rough estimation and must be ignored after the comp. test.

But you can see in the attached file the result of the next comp. test (another movie). AFTER the test: 0.125
Can I belive it? What is the lowest (and maybe true) value that can be accepted?

szabie

[szabie]

2nd attempt to attach jpg:

[szabie]

O.k.
just try to imagine (instead of just looking at a picture:)

Values _after_ the comp. test.
Upper left corner: it is not interesting
Lower right corner: 0.125

so I can reach the 100% (lower center value) easily at 900kBit/s..
:( I don't belive this.

szabie

[manono]

Hi-

The attachments have to be approved first, and we Mods aren't here all the time.

You ran a compression test, so you can then ignore that 0.125. The important figure is the 96% figure. That's quite high (I'd say much too high), and there's even a chance that you won't be able to reach the size you set. That's a pretty compressible movie you have there. It must be a fairly static film, and maybe pretty dark as well. Did you make sure to include the audio size and overhead in the calculations?

[szabie]

Originally posted by manono
Did you make sure to include the audio size and overhead in the calculations?
yes, sure :)


I make a test:
1. compress movie @950kBit/s (=101.4%)
2. after that compress again (the original) @750 kBit/s (=80%)
3. @1300kBit/s (138.7%)

To my mind there will be no much noticeable difference.
Neither between 1. and 3.
Just the size of the avi.
Is that right?

szabie

[jggimi]

I'm not sure how you went from 19% to 96%, since we've still never seen an encoding gknot log file, so I'm not going to guess the possible reasons.

But to answer your questions, if I understand what you were asking about your 3 encodings:

There will likely be no difference in perceived quality between encodings 1 and 3, and little size difference. 100% quality (at the resolution selected, currently unknown to us) as tested would produce a bitrate of approximately 937kbps. Using a bitrate above that (950 or 1300) will not likely be achievable, meaning, you can request those bitrates, but the codec will be unlikely to achieve them. The file size will likely be less than predicted by that bitrate. I use the word "likely" because a comp test is a 5% sampling.

Your encoding 2, at 80% of maximum, should look very similar in quality to the eye to the other encodings. I use the word "should" because video quality is subjective, not objective, and the compressibility best practice guidelines are just that ... guidelines.

[szabie]

Originally posted by jggimi
I'm not sure how you went from 19% to 96%...
this is another movie.
the first was adjusted to ~80% and encoded finally yesterday.

resolution of _this_now_encoding movie will be 640*480


thank you for your exhausting ansver :)

szabie

[szabie]

Originally posted by jggimi
...since we've still never seen an encoding gknot log file....

anyway I have only 2 log files (these are within the program's directory):
- LastCompCheck_GKnot.log
- vdenc.log

which is what you need?
I think the first one, but I can't find any information about bpp in it.
Here is the end of my LastCompCheck_GKnot.log:

>7:47:44: Done.
>7:47:44: Log File = D:\Down\Jurrasic.Park.1.DVDR.HUNDUB\Jurassic >Park1_5_perc_Xvid_LanczosResize_640x336.stats
>Total Encoding Time: 15 minutes, 59 seconds.

Do you need this stats file? I haven't got it. I have no stats file.
Is it normal?

szabie

[jggimi]

You'll find encoding log(s) in the same working directory as your .avi file(s).

They are named <movie name>_Gknot.log

[manono]

Hi-

thank you for your exhausting ansver

Yeah, jggimi wears me out, too, with his exhaustive replies. :)

[jggimi]

I'm tired of this, too. :rolleyes:

[szabie]

Originally posted by jggimi
You'll find encoding log(s) in the same working directory as your .avi file(s).

They are named <movie name>_Gknot.log

there is no such file in that directory after comp test.
only the d2v and the audio files

szabie

[jggimi]

Not after comp test, after encoding... after encoding .... after encoding.

[szabie]

finally I have a movie_gknot.log.
these are the important lines, aren't they?

Quality: 0.176 bits/(pixel*frame).
CompCheck3: 0.000 bits/(pixel*frame).
CompCheck5: 0.220 bits/(pixel*frame).
Resolution: 640 x 352

so I have the 80% of the best quality. am I right?

szabie

[jggimi]

Right! :D

[szabie]

ok
now it's clear

thanks for your patience.

:))

szabie