Two XVID oddities

[wanton]

I have come accross two oddies that happen with atleast koepi 24.6.2003 build. First one is that something in red makes lot of macroblocks atleast with animation even some with quant 2 and lot of macroblocks in quant 4 but doesn't seems to happen with about anything else.

Second one is that if make avi with b frames in it with b frames in quant file is bigger than just p&i frames in quant 2 not much but still bigger some mega bytes (not bits). like one file was 190MB without b frames and about 198MB with them. I also though b frames would be smaller even with same quant but seems that i was wrong.

If anyone can explain why these are happening would be so great :)

[frodoontop]

B-frames are not always beneficial to anime movies. This has been so for quite a while, though it is improving fast. With devapi4 b-frames should reduce filesize. Devapi4 will be having a special cartoon mode I've read somewhere here.
In the meantime always run a compressibility test to see if b-frames are of any help.

[Nibor]

1.
MPEG4-Codecs generally seem to have more problems with red than with other colors.
That's got nothing to do with this build. And neither whith XviD I think. It's 'normal'... :)
This problem is discussed in this thread (http://forum.doom9.org/showthread.php?s=&threadid=38304) for example.

2.
That's normal too :D
B-frames at the same quants as I- or P-frames ARE bigger than these, because they hold 'bidirectional information'...
The trick is that they look better at the same quant. So they can be at higher quants and still look as good as the I- and P-frames..
For example if you have a P-frame at q 2, the next B-frame which is probably in q 4, is still in same quality...
That's why we have "b-frame quantizer ratio" and the offset. The defaults 150 and 75 give B-frames higher quants!

Was this understandable?
Any more explanations needed? :)

-= Nibor =-

[wanton]

No need thanks for your answer it answered everything. And i'll see what that animation setting will bring if it's coming. I wish they could somehow implement setting to xvid code that would check how red scene is and use higher quant for scene with lot of red.

[Teegedeck]

...and this brings us to my often-repeated appeal to anime-encoders: Use B-frames, dammit! :)

[RadicalEd]

Originally posted by wanton
And i'll see what that animation setting will bring if it's coming.

I really didn't notice any big improvements. My testing was only breif (no psnr or anything) but I didn't notice much to any real difference. Then again, it's always possible I did something wrong :\