CRF disadvantage?

[AntiJw]

Hey,
I wonder, is there any disadvantage with CRF (compared to 2-pass) except not knowing how big the filesize will be? I've read about VBV-problems in the past, but I'm not sure if they are fixed..

[Dark Shikari]

VBV-wise, 2pass is better because it can look at the whole video and better distribute the bits to abide by VBV correctly while maximizing quality. In effect, it replaces x264's lack of a VBV lookahead.

But otherwise, there is no significant disadvantage of CRF if you're not in VBV mode.

[AntiJw]

Thanks DS, I'll use 2-pass then, as I'm doing DXVA-compatible encodes (--level 4.1 --vbv-maxrate 50000 --vbv-bufsize 50000), and number of refs according to resolution for DXVA-compatibility.

EDIT2: Sagekilla, yeah, I think CRF is okey on 720p too, although I'll do 2-pass on 1080p-sources (for safety).

[Sagekilla]

@Dark Shikari: A bit related, do you expect we can get the benefits of RCRD using that method you suggested before? I don't remember off hand but you said something about creating trees that would accomplish some of what RCRD was doing without being absurdly slow.

Other than VBV, RCRD was the one other thing that 2-pass had (if you're sadistic) over 1-pass as an advantage.

Edit: If you're encoding for DXVA compatibility, if you stay around crf 19 - 20 and encode @ 720p, you run very little risk of hitting the max rate or overflowing the buffer. I'm not 100% certain for 1080p, but I think it's difficult to break DXVA @ 1080p too. Honestly, unless you're encoding @ CRF 12 you won't have much to worry about :)

[akupenguin]

do you expect we can get the benefits of RCRD using that method you suggested before?
MBRCRD would have even greater benefit than RCRD, and reference-counting AQ would be an approximation of MBRCRD, which may or may not be better than RCRD. In any case, they fall in the same boat as RCRD: they don't require 2 passes sequentially over the whole movie, but they do require 2 passes over each GOP, and the easiest way to implement that is to patch them into 2pass RC.

[Sagekilla]

I don't suppose it would be possible to implement something like that on CRF, would it? I could imagine you can try running a second pass after you complete one GOP, THEN write all the video data for that one GOP. But that would be hacking CRF around a lot.