AutoGK Quality Encoding

[NMachiavelli]

I am curious about this comment from the AutoGK Tutorial:

"I don't think there's much point in going above about 80% because then you'll lose some of the benefits of MPEG4's compression abilities."

I'm a newbie when it comes to this stuff, but what "benefits" is this talking about? Is there a difference between 80 & 100%, just not much? Is it an issue of encoding time or resulting file size or both?

I remember reading about Quantizers when I was trying to figure out Gordian Knot, but know very little about them other than lower quantizer should provide better quality. If the tutorial says Quantizer 3 is used @ 67%, when is Quantizer 2 used? Does any setting allow Quantizer 1?

Quality is my main concern, as I do have an HDTV and want the closest to the original as I can get. At the same time, I don't want to dramatically increase encoding times and file sizes just for the sake of it. Plus, to be completely lame, I don't have the time/experience/patience to do a lot of double blind testing.

Thanks for your time.

[Tuning]

Originally posted by NMachiavelli
I'm a newbie when it comes to this stuff, but what "benefits" is this talking about? Is there a difference between 80 & 100%, just not much? Is it an issue of encoding time or resulting file size or both?

The benefit of MPEG-4 format is to give more compression than MPEG-2. Therefore if you use 100% quality mode there is practically no compression done in MPEG-4 side and you will get HUGE files.

I think Quantizer 1 is equvalent to 100% quality.;)

[manono]

Hi-

It's mainly a question of minimal quality gain, with a large file size gain. That 80% figure is commonly used as a cutoff above which it's not necessary to go. For example, in Doom9's discussion of the Compression Test in his GKnot Guide, he says, "a value above 80% is serious overkill." :

http://www.doom9.org/gknot-xvid.htm

There's no difference in encoding time, just mainly file size, but with no (or very little) perceived quality gain. An 80% quality just flips back and forth between quant 2 and 3.

Tuning-quant 2 is 100%. The only possible reason to use quant 1 is to prevent undersized files. But if you set up a 2-pass encode correctly, there's no reason at all to use it. It just gives you large frame sizes, and as a result, forces higher quants on other frames in order to keep to the desired file size.

[Tuning]

Originally posted by manono
Tuning-quant 2 is 100%. The only possible reason to use quant 1 is to prevent undersized files.

Thanks manono.

:)

[therealjoeblow]

Originally posted by NMachiavelli


Quality is my main concern, as I do have an HDTV and want the closest to the original as I can get. At the same time, I don't want to dramatically increase encoding times and file sizes just for the sake of it. Plus, to be completely lame, I don't have the time/experience/patience to do a lot of double blind testing.

Thanks for your time.

I have a Panasonic CT32HL42, HDTV, with a "build your own" player: a 633mhz PC with ATI Radeon 9200, Svideo TV Out. This player can play any format of digital video, so it's easy to make comparisons without any influences related to hardware variability.

For all practical purposes, neither I or any of my guests can tell the difference between a ~70% xvid encode and the original DVD, both look spectacular on the progressive scan TV. Using ZoomPlayer, if you zoom in to around 2x, then you can see the difference in the encode (although there's no reason to actually ever watch anything zoomed that much), but at native resolution or even zoomed up to 30% (which is how I usually watch ultra-wide 2.35:1 movies), no way, you can't tell.

As a matter of fact, even 50% encodes look *Very* Good on this setup, even though they look marginal at best on a PC monitor (yes, on the HDTV they do look a little softer than the DVD, but it's really quite subtle, and they are still noticeably better than even pure Digital Cable broadcasts).

You should try a few encodes yourself and look at them on your own home theater - don't make a judgement from the PC monitor, because that just doesn't reflect reality of what you'll be watching. If you can't see a difference on your HDTV, then there is no *real* difference in quality.

The real benefit of MPEG4 is space saving - if you're encoding movies, presumably it's so that you don't have to keep swapping discs in and out of your player to watch your favorite movies. A 200GB harddrive can hold quite a few of your favorites, but if you're not really compressing them, then you may as well not bother at all, just use your original discs.

[NMachiavelli]

Thanks so much for your feedback on this! I haven't seemed to be able to find many people who are doing things the way I am setting up. I have a P2.4, with an ATI AIW 8600XT that I'm hooking up with to my 53" Rear Projection TV with the component dongle. I haven't had time to get powerstrip & zoom settings figured out yet, and, like I said, I doubt I'll have the time and patience to do the comparison testing on different quality encodes.

As such, I really appreciate you sharing your experiences on these things.

If anyone else reading this has an HTPC setup with different feedback/advice, I'd be interested in hearing it as well.

[manono]

Hi-

I have a standalone DVD/MPEG4 player that outputs 720p through DVI to a Samsung HLN4365W DLP HDTV. In some ways it's even better than the HTPC setup that you guys have (and in others, not as good). But I agree with everything Joe said. They look better on the TV than on the monitor. You don't even need as high as 70% quality to get a really good rip. I would say that anything over 67% (quant 3) for clean sources is pretty good, and reasonably close to DVD quality. For old noisy movies, 50% is quite good.

they are still noticeably better than even pure Digital Cable broadcasts

I don't know if it's true where you are or not, but where I am, digital cable is just converted from analog, and not a pure digital signal. The only way to get true digital where I am is from satellite. So for me, digital cable is only marginally better than standard definition. So any and all of my XviD movies look way better than anything that comes over the cable.

[therealjoeblow]

Originally posted by manono
Hi-



they are still noticeably better than even pure Digital Cable broadcasts

I don't know if it's true where you are or not, but where I am, digital cable is just converted from analog, and not a pure digital signal. The only way to get true digital where I am is from satellite. So for me, digital cable is only marginally better than standard definition. So any and all of my XviD movies look way better than anything that comes over the cable.

Same deal here with all of the broadcast channels, simply analog piped through an expensive box. However the 6 Movie Channels that I get (Movie Central, Adrenaline Drive, Shadow Lane, etc) are pure digital. Problem with these, though, is that Shaw Cable doesn't have the bandwidth to provide quality signals, so they crank the Mpeg2 compression way up, resulting in very soft-looking signals, with noticeable blockiness in dark scenes. It really looks like a mediocre quality DivX3 encode from about 3 years ago, before anyone figured out SBC :(