[x264-devel] preset veryfast always generates lower bitrate than veryslow. Why and how to fix?

[Steven Walters]

> This just statistically contradicts your statement:
>> There is a correlation between the settings and size that has a
>> _tendency to occur_, but in no form is there any guarantee (causation)
>> about it when using CRF.

?
I don't see how this is a contradiction.
I said there is a tendency for the filesize to get smaller with slower
settings, which you've indicated with the data.
but I did not say that this guaranteed to occur, because it is indeed
NOT guaranteed to occur.
(tendency does not mean 100% of the time after all.)

Though in reality, none of this is particularly related with the
presets, which you are seemingly solely fixated on, but instead this
is the behavior of CRF in general.
But moving on...

>
> Other way around:
> Is it too complicate to check whether the part of the code converting
> "preset" into really used parameters is written correctly, specifically
> for veryfast?
>
> I would do it myself (it is c/c++/asm, correct?) given someone can guide
> me up to some extent at least saying where is the relevant piece of code.

By all means go look for yourself, the presets are defined at [0],
though you'd likely also need to compare against the defaults which
are the "medium" preset, which are defined at [1].

These are fairly straight forward/simple, so this should not take one
long to review.
As the code indicates, "veryfast" does indeed use settings "that are
in between" "superfast" and "faster", so does this satisfy your
request?

In the end, this is a behavior that users familiar with CRF in x264 are used to.
Also, we don't develop x265, so comparing against that feels like
comparing apples to oranges.

[0] - http://git.videolan.org/?p=x264.git;a=blob;f=common/common.c;h=029f7b39348c8c538335641f18d7cbfd9e004bf5;hb=HEAD#l182
[1] - http://git.videolan.org/?p=x264.git;a=blob;f=common/common.c;h=029f7b39348c8c538335641f18d7cbfd9e004bf5;hb=HEAD#l47