XviD only uses two different quantizers

[Die Kuh macht Muh]

I encoded a video with XviD using target quantizer = 4. I then ran DivXDRFAnalyzer on the encoded video. It said quantizers 4 and 7 were used, but no other quantizers. For 66% of all frames, q=7 was used:

http://pikki.net/u2y222k

That surprised me because with target = 4, shouldn't it use q=4 for most frames, q=3 and q=5 for others and maybe q=2 and q=6 for the rest? What made it pick q=7 for the majority of the video?

There are 66% B frames in the video, so could it be that q=4 was used for I and P frames and q=7 for B frames?

Would I get different results if I did a 2-pass encode?

[Awatef]

That's normal.
If you disable b-frames, you'll get quantizer 4 all the way through (=> higher file size, quality increase questionnable), so you guessed right, q7 was used solely for b-frames (this is controlled by the quantizer ratio you set for them, it's 1.5 by default).

And no, 2-passes won't change anything, and has no sense when encoding to a target quantizer. 2-pass encoding applies when you need to hit a given size, say when you need a specific bitrate w/ highest possible quality.

[foxyshadis]

If you turn on the encoding status window, it'd show all that there. And xvid has nothing like x264's crf mode, so only the actual quant you use (or two quants that average out to the fraction you input, if it's not a whole number) will get used.

(One of DRFanalyser's big failings is that it mixes i/p and b frames, though their quant ranges really should be viewed separately.)

[Valeron]

if u need to take a deep look into this matter to reveal what's happening, enable the OSD function with Frame Mean Quantizer tag in ffdshow can show u up quantizer used frame by frame.