make XviD react quickly?

[jkwarras]

Hi,

I was doing a DVDRip with latest Koepi unstable build (22/03/2003) and i notice that with 1 pass QB the codec makes too much time to react to the needs of the scene encode. At least at the beginning of the movie and the end; Let me explain.

The first 30 sec was a black screen with initial credits on it, so the codec use around 150-250 kbps on it, and suddenly there's an action scene, the bitrate start to move up, but it takes like 1 min to achieve something like 700 kbps. At the end, same thing, the last scene just end butraly, the credits begin and the codec spend around 1500 kbps on it! A normal credits, black with white letters rolling up!

I'm doing 1 pass QB and i'm very happy with it, the only question i have is if there's something we can do to make the codec react quikly to changes in bitrate needs.

The settings i used: 1 pass QB 93-97% (it depends on the movie); bframes 3, DivX5 compatibility on, Packed bitstream on, GMC on, New modulated HQ, I and P max min settings set to 2-31.

Thanks

Superfly

[APF_Gandalf]

if you looked at the "bitrate" that virtualdub shows when encoding, you are wrong, it's an average bitrate, not an instant bitrate.

[NoLogo]

My guess is the bitrates jkwarras gives us are the ones shown by FFDShow...

Whatever, jkwarras, uncheck "packed bitstream", it is know to be little buggy for quite a long time.

@all devs
About "packed bitstream", why does that option still appears in the codec window ? Would it really be usefull if it'd work ?

Regards
NoLogo

[Sigmatador]

it's usefull for streaming i suppose

[kastro68]

Try using High curve aggression under Alternative curve compression.

But I would only recomment using this if you are encoding anime.

[jkwarras]

[QUOTE]Originally posted by NoLogo
My guess is the bitrates jkwarras gives us are the ones shown by FFDShow...

That' s right. I know that the values that are given by ffdshow are not very accurate, but this is the only way that i have found to check this out. Still can see it just looking at the image, the scene is a high motion so if you stop it every 10 sec you can see blocks around edges, and the become less visible as the time pass, but the scene is as fast as the beginning (1 min ago).

I know, is not a big deal, just wondering if i can make it better and quicker :)

Whatever, jkwarras, uncheck "packed bitstream", it is know to be little buggy for quite a long time.

I start using it to avoid two problems:

1) When you try to cut or edit the encoded movie in Vitualdub, if you go forward (snipping to keyframes) all goes fine, but if you go back then you notice that the series of frames that dub are showing are not the same as when you go forward; it's a little satrnge, i assumed it's because the way that XviD put bframes and i and p frames.

2) Get rid of the following message when i open a movie : b-frame lag or something like that. Then the movie just play fine, bt with "packed bitstream" it just don't show it anymore.

[jkwarras]

[QUOTE]Originally posted by kastro68
Try using High curve aggression under Alternative curve compression.

As i' m using 1 pass QB i can't use this :) I guess that there's no way to improve that.

[sysKin]

jkwarras, you've got it all wrong. In constat quality mode, xvid does not 'react' to any bitrate needs - the whole ratecontrol is inactive. All xvid does is keeps constant average quantizer and is not even aware of the bitrate.
The bitrate values you quote don't look right because of the method they are computed - it's an average bitrate, and it's no wonder that average can't change dramatically.
If you want to see bitrate over a smaller time, look at vdub's graph.

Radek

[drebel]

Any news about "packed bitsream" and audio synch probs with .avi container?Does "save as ogm" option in virtualdubmod (directly and not when muxing audio or else) solves the prob by taking full advantage of the capabilities of the container?
Even if "b-fr decoder lag" is not really a prob,it would be nice to know if there's a workaround for it...

regards,
george

[kilg0r3]

Originally posted by sysKin
In constat quality mode, xvid does not 'react' to any bitrate needs - the whole ratecontrol is inactive. All xvid does is keeps constant average quantizer and is not even aware of the bitrate.


Whoops, he is not the only one. I always thought this would be more like a one-pass vbr mode, modulating a quantizers in a range of +/-1.

[jkwarras]

Originally posted by sysKin
jkwarras, you've got it all wrong. In constat quality mode, xvid does not 'react' to any bitrate needs - the whole ratecontrol is inactive. All xvid does is keeps constant average quantizer and is not even aware of the bitrate.

Really? I don't think so, but maybe i'm really wrong. This encoding thing is a learning everyday lesson :)

I'm using 1 pass Quality base, not the 1 pass quantizer. With 1 pass Quantizer, the codec don't react; The codec does a CBR encode with the quantizer set.

In 1 pass Quality Based I set the max and min I and P frame to 31 and 2, so the codec can go up and down in the maximum range. As i have read in many guides and as reported on other topics, the Quality Based (where you set a %, more or less equivalent to the DivX quality based) is a real VBR mode. If i see the Vdub window when i encode the movie the bitrate change, not readically, but it change. So i guess is VBR, but it keeps the overall quality constant (or average).

I know that there's a lot of discussion about that, but i think that this is best that a 2 pass VBR, because is a real VBR, the 2 pass is more like an ABR. BUt is only a matter of taste anyway :)

[kilg0r3]

quoting xvid options explained

The "1 pass quality" mode
This mode is already known from DivX4. In this mode, all frames get the same amount of compression - regardless of the complexity of the frame. This mode is useful if you want to reencode the material you're compressing this way. The equation used for this is: ((MaxQuant-MinQuant)/100 * (100-quality)) + MinQuant

The "1 pass quantizer" mode
This is another type of quality mode. If chosen, a fixed quantizer will get used, for example if you enter 3 here, all frames get compressed with quantizer (= level of detail removal) 3, resulting in a real constant quality. The difference to the 1 pass quality mode is, that here a fixed quantizer gets used, while in 1 pass quality the quantizer is modulated a little.

[sysKin]

Originally posted by jkwarras
[B]I'm using 1 pass Quality base, not the 1 pass quantizer. With 1 pass Quantizer, the codec don't react; The codec does a CBR encode with the quantizer set. No no, 1 pass quantizer is not CBR. 1 pass quantizer is a special case of 1 pass quality: In quantizer mode the all frames will have the same quantizer (as set in the config) while 1-pass quality allows 'fractionl' qualtizers and if you set it to 2 1/3 (and this corresponds to some percent, for whatever reason) the quantizer will modulate '223223223...' and the average will be 2 1/3.
I know that there's a lot of discussion about that, but i think that this is best that a 2 pass VBR, because is a real VBR, the 2 pass is more like an ABR. BUt is only a matter of taste anyway :) Ok there is prabably a typo here ;) so I'll just explain:
1 pass quantizer/quality - true vbr, with constant average quantization
1 pass CBR - it's actually ABR - constant average bitrate
2 pass - true vbr, similar to 1-pass quality but with automatic curve scalling and adaptation (so you don't have top 'guess' quality setting).