no-mbtree yields smaller filesize than high qcomp?

[Zaxooz]

Hi everyone,

How is it that with no-mbtree on I get smaller file size than with qcomp set to 0.75? I though that driving the qcomp to 1.0 would essentially mean switching off mbtree, but it somehow manages to surpass it in bitrate well before that point.

I am obviously referring to same crf encodes.

[colours]

CRF is a well-defined quality metric only if you keep all the other parameters identical. Of course, if you modify the qcomp/mbtree parameters, iso-CRF encodes aren't quite iso-quality anymore, so you're comparing apples to oranges.

Obviously, you're not supposed to do that. (Protip: what is "obvious" to one might not be obvious to another. Don't assume everyone is on the same wavelength as you.)

If you want to compare x264 settings, use 2-pass encodes with a fixed bitrate, or 3-pass if you want to make sure x264 is hitting the target bitrate really closely. Pick your favourite combination of settings, then make your fixed-CRF encodes.