Quality x File Size x B-Frames Quality limit in Divx5?

[DivxBr]

I made some encodings with the new DIVX 5.0 codec and a lot of questions arise to me:

1. In constant quality (100% - or quantizers = 2) with B-Frames, the file in Divx 5.0 is smaller:

Ok, smaller files with B-frames; but I read in this forum that the codec scales the quantizer in B-frames (so, the quantizer aren´t 2 in B-Frames?). If the quantizers aren´t 2 in B-frames, we can tell the quality is 100%????? :confused:

2. Since Divx 4, I´d used several times, the divx codec in the 100% quality mode, but frequently, I get lost details in dark and constant colour (low contrast) areas. This mean that the 100% quality mode is far from being near-lossless codec? :confused:

3. With MPEG2 (DVD), as I concern, if we raise the bitrate we get always an increase in quality and filesize until the moment we get a lossless compression. (it is possible?). If Divx5 (MPEG4) has a limit in quality/file size (in the moment when all the quantizer reached 2, but the quality isn´t near-lossless) unlike mpeg2, there´s a limit in the quality we can achieve? :confused:

I´m confused,

:confused: :confused: :confused: :confused: :confused:

[theReal]

mpeg4 and mpeg2 will never be lossless, the algorithms use mechanisms that are lossy, no chance to avoid it.

Then, you're right, b-frames do not use quantizers of 2 in 100% quality mode, but because they are b-frames they are supposed to deliver the same quality as if they were normal quant 2 frames. I personally think they do, but if you can see a difference, turn b-frames off.
As you already said, Divx 4 at 100% quality isn't literally 100% like huffyuv - just like 320 kbit mp3 is never the same as uncompressed wave.

Encoding is making compromises...

[DivxBr]

I know, we can´t achieve lossless compression in MP2 & MP4, that´s because I used the term "near-lossless".

I´m thinking if the "top-quality" of the Divx5 codec isn´t too low, as soon we can´t raise the bitrate above a certain level (when all the quantizer turn to 2), when still remain some clearly visible artifacts in the output. :(

I´m thinking too if the competition for lower filesizes everytime isn´t throwing the quality parameter out.

Maybe if we could get a codec with option to use quantizer 1 (is it possible?) ?!?! (or even quantizer 2 with less artifacts).

As with MP3, if we get distorted sound when using 128 kbps, we can raise the bitrate to 160, 192, 224, and so on... But,... if the maximum quality of a MP3 codec was set to 128 kbps, it would be acceptable for the most, but if we can´t raise above it, our top quality will be only,.... acceptable.

[dragoman]

Hi,

DivX5Pro is far more dependent upon quantizers (because of the addition of b-frames) than is DivX4.

The bitrate setting (quite often) is not the deciding factor as to your final filesize.

I have encoded two movies with DivX5Pro with b-frames at 100% quality. Gladiator, which is 2hr, 35min long video took 1.6gb of space at DVD resolution.

Xmen, which is 1hr, 35min long at DVD resolution video took up 850mb.

Both look incredible. I used ac3 sound for both, so Gladiator is a 3-cd rip (which I don't care about, it's an incredible movie) and Xmen is a two-cd rip. Quality....outstanding.

My opinion is the 100% quality encode is great for those who don't really care about #of discs, only quality. Most movies under two hours will come out to 2 discs anyway, only the really long ones are 3. I find that an acceptable price to pay for such quality at DVD resolution.

As for min quantizers, DivX has a min of 2. Xvid, however, has quantizer 1 capable encoding, but filesizes are very large. And I don't think Xvid can compete with DivX 5 Pro right now at 100% quality setting...

All in all, I am very satisfied with DivX 5 Pro...

dragoman