H264 Colorspace & Other Issues

Infinity Squared · Post by **Infinity Squared** » Wed Oct 24, 2007 10:05 pm

Ok, so I've been wanting to preserve as much quality out of my latest video as I could. Naturally, H264 is a preferred mode of encoding and though it yielded a result that's superior in terms of size and quality compared to an XviD attempt, I was still not satisfied.

During dark patches, in particular when fading from black to the dark patch, the macroblocking is very noticeable. My first question is, is there a method/setting in which I can encode in H264 where I can tell it to assume a less intensive averaging to have smaller, less noticeable blocks?

The other thing I've come to notice are sometimes pale gray/ghostly green kinds of blocky flickers occuring in conjunction with the macroblocking during the dark patches in the screen. Screenshots don't reveal them, so I can only summise that they're somehow a temporal problem. I was wondering, can you encode H264 without having a YV12 colorspace as the input?. My logic behind the question is purely a gutt feeling rather than something I can substantiate by any evidence.

For people's information, I've currently got 2 encodes in H264. One is done in 2 passes, bitrate of 2100kbps (I know it's a lot

), and file size is 56MB. The other was done in quantizer 17 and comes in at 80MB. I'm of the opinion that there's no significant quality difference between either, and I could probably peg down the 56MB version and still not get much reduction in quality. However, the problem still persists in both cases.

Any takers?

Phantasmagoriat · Post by **Phantasmagoriat** » Thu Oct 25, 2007 12:11 am

I'm probably not the best to say anything, but what program do you use to encode? because meGUI has a lot of features, such as Zones-- similar to XviD, where you can specify a constant lower quantizer just within the part of your video that has problems... then again, I don't know if lower than 17 would make a difference.

as for the rest of your questions... I wish you luck.

Infinity Squared · Post by **Infinity Squared** » Thu Oct 25, 2007 12:15 am

Well, I'm just using Zarx's program.

Rapture** · Post by Rapture** » Thu Oct 25, 2007 3:18 am

IIRC,Zarx264 does not allows to use other colorspace than YV12. It's just as Phantasmagoriat said,it's all in the encoders.

Qyot27 · Post by **Qyot27** » Thu Oct 25, 2007 6:26 am

I know that the 'no fast P-skip' option is intended to reduce blocking in solid areas of color (mostly blues, if I remember correctly) - maybe that might help with the black? Adaptive quantization probably would affect it also. Maybe even Chroma ME might.

Granted, I'm not familiar with what settings are used or available in Zarx's program (I use MeGUI), so I don't know if what I've said makes any difference, but as far as I'm aware, those will probably take care of the fade macroblocking issue.

As for the green artifacting, it sounds familiar, but I'm not sure what it's caused by - it could be that that issue is also prevented with the solutions I highlighted above.

Phantasmagoriat · Post by **Phantasmagoriat** » Thu Oct 25, 2007 10:02 am

thought I should add, that meGUI also makes you add converttoyv12() to the end of your script just like Zarx264, so I suspect it is something that's required. Also, http://i162.photobucket.com/albums/t244 ... UI_cap.jpg
[I like this layout for zones more than Xvid's

]

whatever isn't within a Zone will be encoded using settings from the Main tab, so you don't needlessly use a lower quantizer for the areas that look the same at a higher quantizer... so you'll save on file size, and retain awesome quality.

come to think of it, this is the only feature of meGUI that I do use. It'd be nice if it was part of Zarx264... but automation is good too.