AutoGK - Bigger file = better quality?

[kelemvor]

Howdy,

I'm experimenting with AutoGK to convert a DVD Movie into an Xvid/Divx file. I started it up encoding and gave it a 1 gig size limit. It said the percentage was estimated at 67% or so.

I used this guide as a sample to follow:
http://www.rita.lt/guides/AutoGK_DVDtoAVI.htm

I then did the same file again but gave it a 1400 size limit. I thought it'd be better quality but it still said it was estimated at 68%.

Does giving it a bigger size not necessarily guarantee a better quality file? I'd like it to look as close to the original DVD quality as I can get while still getting at least 3 movies to one DVD.

Any other settings I can try or should I not expect to get better than I am?

I'm brand new to this so if there's other software or other settings or anything else I can do, please let me know. I also don't care if it takes 12 hours to encode, time doesn't matter either.

Thanks for any tips.

[disturbed1]

When final size isn't an issue I usually use a constant quant of 2. This tend to yield the best picture quality. Depending on the film, some movings come out huge (3gig Apocalypto) and others at a decent size (900mb Wild Hogs). I don't notice any quality difference using a Philips DVP642 on a 52" HDTV. But I'm not looking at the film through a magnifying glass either.

To stick to 3 movies per DVD, you'd have to make each movie 1/3 DVD size. The quality will vary with each movie, from bad,good, to great, depending on the film.

[kelemvor]

What exactly do you mean by

a constant quant of 2?

[manono]

Hi-

Does giving it a bigger size not necessarily guarantee a better quality file?

AutoGK aims to wind up with around 70% or so in the compression test and adjusts some of the variables accordingly. As a result you can have 2 AVIs of the same movie of very different sizes but roughly the same quality percentage. If you compare the 2 AVIs, you should notice that the 1400MB one has a higher resolution than the one of 1000MB. For a more detailed answer I'd need to see the 2 logs. But to answer the question; because one has a larger resolution as well as file size than the other, even though the quality percentage is the same, the larger one should be sharper, clearer, more detailed, and, yes, better. But again, to say anything definitively, the logs would be needed.

What exactly do you mean by a constant quant of 2?

AutoGK's version of a constant quant encode is the 1-pass Target Quality (in percentage) encode. If you did one for the default 75%, you may find a final file size even larger than the 1400MB 2-pass encode you did. If you did one at 100% quality (roughly the quant 2 disturbed1 mentioned), it would wind up quite a bit larger. For more information you might try reading the included tutorial. It's also available online here:

http://www.autogk.me.uk/modules.php?name=TutorialEN

[disturbed1]

Hi-


AutoGK's version of a constant quant encode is the 1-pass Target Quality (in percentage) encode. If you did one for the default 75%, you may find a final file size even larger than the 1400MB 2-pass encode you did. If you did one at 100% quality (roughly the quant 2 disturbed1 mentioned), it would wind up quite a bit larger. For more information you might try reading the included tutorial. It's also available online here:

http://www.autogk.me.uk/modules.php?name=TutorialEN

Quant 0 = 100%
quant 2 ~80%, quant 3 = 67%

[manono]

There's no such thing as quant 0 (as far as I know) and AutoGK doesn't use quant 1. It's hard to give precise percentage vs quant figures these days because DivX does it differently than XviD and B-Frames affect things greatly. Traditionally quant 2 was 100%, quant 3=67% (2/3=0.67), quant 4=50% (2/4=0.50) and so on. And remember that the OP's questions are about AutoGK and not the settings one might use when doing a manual encode.

[kelemvor]

I did do a test and got some pretty close results.

I was using Pursuit of Happiness as a test.

I did a conversion and set the quality yo 75%. File ended up being 1.5 gigs. Compared to the 1.4 gigs I got when I set it to 1400 it's pretty close. I never noticed the resolution before but I checked now and it is definitely different. 720x304 vs 704x288

I think I'll do a few more tests by just setting it to 75% and see what sizes I end up with. Is that what most of you do or do you do the file size type?

Thanks.

[manono]

Is that what most of you do or do you do the file size type?

It depends. Doing the 1-pass is definitely faster. If final size isn't important - if burning to DVDR, perhaps, or keeping the files on some sort of a media server or HTPC - then you may prefer to use the 1-pass method. If you have to have them for a specific size (as when burning to CD or a set fraction of a DVDR as disturbed1 mentioned), then you'll want to use 2-passes.

By using 1-pass you lose complete control over filesize but can be assured of even quality for all the AVIs you encode (if all done for the same percentage). But because different movies compress differently, you can get huge differences in size. Just compare the sizes he got for Apocalypto and Wild Hogs with the same 1-pass quant 2 settings (encoding manually). Apocalypto is one of the more hard-to-compress movies ever made. The differences in length of the 2 movies only accounts for a part of the differences in sizes. It's all that running around in the jungle that makes Apocalypto so much larger.

[kelemvor]

It's all that running around in the jungle that makes Apocalypto so much larger.

So for the best compression I should stay away from Jungle Movies? Got it. Thanks for the tip. heh heh.

I have a few movies to play with so I'll just do them each with various settings and see what i get.

Thanks.

[jagabo]

Basically, with constant quantizer or constant quality encoding you specify the quality and the file turns out whatever size is required to achieve that quality. With 2-pass VBR, you pick the file size and the encoder gives you whatever quality it can for that size.

[EAO]

Curious about similar.

Are there 'easy to use' custom quantizers that may be used to improve what 'gk' is doing? If so, then where and how to use? Are there any tutorials regarding this part of autogk?

[manono]

Hi-

Are there 'easy to use' custom quantizers that may be used to improve what 'gk' is doing?

You said "gk" which is usually interpreted as Gordian Knot. If you meant to say AutoGK, then the closest thing it has to a constant quant encode is the 1-pass Target Quality (in percentage). It's discussed in the included tutorial to which I linked earlier.

[kelemvor]

THere's no way to do an either/or type thing is there?

I'd like to say go up to 1.4 gigs of file size unless a 75% encode would be less than that, then just go up to the 75% quality.

[manono]

There's no way to do an either/or type thing is there?

No, you'd have to do one of each and then choose the one you prefer.