x264 and crf

[Anacletus]

Maybe it's a dumb question but i keep getting an average Q of 20 whenever i run CTs on my bluray rips with x264 set at CRF 18.

I wonder why the resulting video does'nt have an average quantizer of 18??

Any help is appreciated.

TIA
Anac

[buzzqw]

use avinaptic, and look at crf of I frames, P frames and B frames

... then look at your encoding string :)

BHH

[LoRd_MuldeR]

Maybe it's a dumb question but i keep getting an average Q of 20 whenever i run CTs on my bluray rips with x264 set at CRF 18.

I wonder why the resulting video does'nt have an average quantizer of 18??

Any help is appreciated.

TIA
Anac

Why should it? CRF never claimed to give an exact average quantizer. It gives a constant rate factor - the CRF value you specify will be converted to a rate factor value internally. Normally you'd specify a rate factor instead of a CRF value (quantizer). The developers simply tuned the internal "CRF value -> rate factor" function in a way that you will get an average quantizer that is in the range of the specified CRF value. That's intended to make it easier for the user to switch over from CQP mode to CRF mode. But it isn't exact! The same way like CRF doesn't give perfect "constant quality". Usually it's constant enough that you can find your preferred CRF value and use that value for your future encodes. But that's it...


use avinaptic, and look at crf of I frames, P frames and B frames

As far as I know the "DRF" values displayed by Avinaptic are useless, if VAQ was used.

See: http://forum.doom9.org/showpost.php?p=1205151&postcount=14

[Anacletus]

mmh thanks both for the explanations.

I guess i'm going to need some more study about this matter after all

:thanks:
Anac

[buzzqw]

@LoRd_MuldeR

good to know, thanks

BHH