How does the XVid quality base encode works?

[duartix]

It's probably the same as DivX right?
But what does a value of 85% quality mean?

I find this option a lot useful to me for encoding music videos since I don't mind about filesize but just getting good enough quality and stuffing a few dozens in a CD.
As a bonus I only have to do one pass.

[-h]

The quality mode is currently a bit different to DivX 4.x.

All it does is select an 'average' quantizer to use throughout the clip. That is, if the equation ended up with 3.5, your clip would be encoded using 3, then 4, then 3, then 4, then 3 etc. as quantizers for the frames.

The equation used is:

((maxQ-minQ)/100) * (100-quality) + minQ

Therefore, if you set your min quantizer to 2 and your max to say 27, encoding with quality = 85% will give you:

((27-2)/100) * (100-85) + 2
= 5.75

So your clip will encode with 5, 6, 6, 6, 5, 6, 6, 6 as the quantizers. This works the same as DivX4, but it doesn't pay attention to the min/max quantizers like XviD does, so you can't guarantee that identical quality settings will actually result in the same quantizers between XviD and DivX4.

It's actually easier, in XviD, to set the encoding mode to "1 pass - Quantizer" and enter 3 or 4 or even 5 as the quantizer to use. It'll achieve the same thing as 1-pass quality mode, but save you the math :)

-h.

[duartix]

That's as much as I needed to know.