what does aq affect look like?

[Enrico Ng]

I did a couple tests with the newest XviD beta.

I used a DVD as my source.
The clip was 20min long.
I did 5 quick tests
VHQ=1 for all
Chroma Motion on for all I think

1. defaults
2. AQ
3. AQ and B frames (defaults)
4. GMC VHQ=0
5. H.263 with trellis

It was very difficult for me to tell any of the resulting clips apart, To me, they looked almost exactly the same. I though that the one with the B frames looked better. I thought the one with GMC looked the worst

I was curious, How should the video look with AQ enabled. The description says that the dark parts are compressed more, but I'm not sure what this should look like.

I noticed that sometimes the gradients do not look good. Like if its a dark room with the door open to a lighted hallway, the gradient from light to dark on the door is not even at all. but maybe this has nothing to do with the settings.

I'm not sure, should I beable to see a big difference? I tried those settings because I had tried them before with the old XviD and I usually saw almost no difference or it got worse. Now, I basically just see almost no difference. Are features like AQ, Bframes, only useful for longer clips, like 2 hour movies?

I aim for about 17.5mb/min including 128kbit cbr audio. Is my bitrate too high? At these bitrates, are the differences suppose to be not noticable?

Thanks

[sysKin]

Heh, that's 2205kbps ;) I'm reasonably sure you won't see much of a difference here ;)

Radek

PS. Yes, GMC without VHQ makes the quality worse in most cases. Use at least VHQ1 with GMC.

[digitalman]

I do not see much difference either between settings when using a high bitrate such as 2700kbps. I like to put two movies on one DVD, so this is why I use such a high bitrate. B-frames do seem to make a little difference though. I see a large difference in quality between XVID and DIVX at higher bitrates, with XVID being way better in quality. But that is all subjective and I am sure many may disagree.

[Enrico Ng]

Ah, so AQ makes little difference with high bitrates
I had read it was good for darker movies.


I also ran some tests with VHQ4 and it still looked the same.
I guess if I am at a high enough bit rate, the settings don't make much difference.
I have noticed a tiny tiny difference with B frames though

[Teegedeck]

If you don't see differences easily you are in fact fortunate. For it means that you can either use strong compression or encode faster because you don't need to use all of XviD's features. This is no joke, quality is subjective.

If you absolutely want settings that let you see differences, try quarterpel or a custom matrix (HVS-best-picture matrix springs to mind).

Edit: If you are determined to spot differences at high bitrates, you have to look somewhere where the human eye is used to differentiate a lot: Try actors' faces, the skin structure, to be precise. Does it look realistic; does it shape your idea of the face's dimensions - or is it just a flattened area? Here you will notice more easily the difference made by any filter you choose, any higher quantizer or different quant-matrix.