[x265] Severe quantizer difference between {...faster} and {fast...} presets

[Steve Borho]

On Tue, Feb 11, 2014 at 3:44 AM, Deepthi Nandakumar <
deepthi at multicorewareinc.com> wrote:

> Hi,
>
> Between faster and fast, a number of key default options change. In order
> of effect, the options that cause this would be bFrameAdaptive (jumps to 2
> in fast), --early-skip, --fast-cbf, and then --max-ref. (Assuming you have
> already disabled cutree in fast preset).
>

The jump to --b-adapt 0 is most likely responsible for most of it.  We
currently use 0 for the faster presets because performance falls off a
cliff on servers if you use --b-adapt 1 and it fails to find many B frames.

It's something we're constantly trying to improve so that we can use
--b-adapt 1 at those presets; but HEVC frame parallelism is a tough nut
because of the large CU size, there's many fewer rows so fewer frames can
be in flight at once.

-- 
Steve Borho
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