Quantizer Question

[weaver4]

Can someone explain how decimal quantizers work? I see that the XviD codec will allow quantizers set to decimal value (like 2.7). But isn't the quantizer only a whole number? When I run a movie three times with quantizers of 2, 2.7 and 3 the 2.7 filesize is between the filesize of 2 and 3; so it is having some effect.

[Sagittaire]

1) quantizer can't be decimal for block
2) quantizer can be decimal for frame if you use adaptative quantisation

With XviD if you choose q2.7 for quality mode RC will choose alternate between quantizer 2 and quantizer 3. At the end average quantizer by frame will be ~ 2.7 ...

[Caroliano]

And if you don't use adaptative quantization, you can still put the average quantizer for 1pass as 2.7. In that case, it will alternate between quantizer 2 and 3 in the frames to get an average of 2.7 in the whole movie.