[x264-devel] Encoder questions

[BugMaster]

On Fri, 23 Nov 2018 12:11:29 +0100 (CET), vpstranger at tutanota.com wrote:
> Finally, there you are. I want you to answer questions without
> reminder. I understand that you do it when you have time, but simply
> ignoring them is just obnoxious - don't do that.

First, you should understand that nobody is obligated to answer your
questions. Second, questions that don't have anything with x264
development (patches discussion, bug reports, feature suggestions,
etc.) have lower priority and can be even ignored (if it is decided
that answering is waste of time that doesn't provide any benefit).
Third, being pushy and offensive wouldn't help and may backfire by
lowering priority of your email.

> Now for the subject. What linux kernel or anyone else uses is not
> an argument, because everyone, including Linus Torvalds, is prone to
> stupidity or bad habits: we're all just humans. So you must make your own decisions.

No comments (I already said what I wanted).

> As for the encoder, I need to clarify something. You say 8*8 is not
> always better. In what sense better? Compression or quality? Can you
> explain it comprehensively or give a link to a paper or book chapter
> where this point is explained in such way?

Compression and quality is the same thing for lossy encoder which try
to find optimal point at this curve.

> Then you said about b-adapt algorithm. I looked up the x264 paper
> by Loren Merritt, but it describes this choice just briefly, and I
> need more detail. It says there's a low-res ME run for each couple
> of alternative frame sets, but is it a full-featured ME or is it
> further truncated in some way? Also the parameters include 2
> versions of it, fast and optimal, and I want to understand the
> difference between the two. Actually when I tried to switch from
> fast to optimal, leaving other pars untouched, I got a bigger
> bitrate in my test encode, which is the opposite of what I expected.

If you want details than read source code.

> And the last question that is the most crucial. When I used the CRF
> mode and compared it to CQ of the same value, I noticed that it
> often  increases and decreases the QP in very unnecessary frames. So
> if the QP choice for CRF is based on the amount of frame motion as
> described in the paper, then maybe it will give better results when
> using a different frame evaluation method from 2-pass VBR mode. So
> the question is: can I use the CRF mode in conjunction with an evaluation pass?

You can use CRF for 1-st pass of 2-pass encode. If you mean other way
around than no CRF pass doesn't need and can't use 1-st pass statistic.