Calculating file size in CRF

[Chengbin]

If you know the file size of a video file in a CRF value, what formula should I use to calculate the file size in other CRF values? (If you don't mind, could you type it in latex? Thanks.)

[Dark Shikari]

~ +6 CRF = half filesize

[martinfrombern]

this one doesn't need latex :)

size_with_CRFy = sizewithCRFx*1.125^(x-y)

[Chengbin]

~ +6 CRF = half filesize

You mean - right?

So CRF is logarithmic? Ahh, I hate logs. Anybody mind showing me an example to refresh my memories?

Say CRF 18 is 100MB, and I want to find CRF 20.

[J_Darnley]

The bitrate produced by crf will roughly follow the qp-bitrate relationship: new_bitrate = old_bitrate * 2 ^ ( (old_qp-new_qp) / 6 )

Therefore: crf=18, filesize=100 -- crf=20, filesize=79.4

[kemuri-_9]

You mean - right?

no it's positive: every raise of QP/CRF by 6 'points' halves the bitrate.

this could be applied in vice versa as well: a decrease of QP/CRF by 6 'points' doubles the bitrate.

[martinfrombern]

Say CRF 18 is 100MB, and I want to find CRF 20.common man, you have the formula above, if you don't know how to than look into basic math book. this is not a place for question like this

[Chengbin]

no it's positive: every raise of QP/CRF by 6 'points' halves the bitrate.

this could be applied in vice versa as well: a decrease of QP/CRF by 6 'points' doubles the bitrate.

Dark Shikari edited his post right when I pressed quote.

@J_Darnley

Thanks for the formula. I'm surprised it doesn't need logs.