[x265] [PATCH] Basic support for tweaking rate control using zones

[Tom Vaughan]

Fair question.  For everyone's benefit, especially Adam Marcus who
contributed the patch, I should explain what's going on in this section of
the code.

Of course there is some "cost" to every new feature (in complexity and the
need to maintain it).  x265's rate control is significantly more complex
than x264, due to WPP and frame parallelism.  At any given point in time
there may be 5 or 6 frames in varying stages of completion, and typically
you don't want to change the base QP mid-frame.  We've also added new
features we've added to handle special cases that arise due to frame
parallelism (ABR reset, etc.).  We're also developing a new CBR variant of
ABR with VBV.  It is challenging to deliver rock solid rate control under
all possible scenarios, and when rate control can't handle certain
material you run out of bits somewhere, QP goes through the roof and you
get visible distortion.  We have a number of important customers who are
putting x265 into commercial production, and we get feedback (along with
content samples, steps to reproduce, etc.) when x265's rate control
doesn't handle a particular combination of settings and content optimally.
These customer requests have been driving a lot of the rate control
patches/improvements that you've seen over the past months.

We weigh the cost against the benefit.  We like the basic concept of this
patch - the ability to uniquely adapt x265 to different segments within
the video title.  This type of capability fits in with our long-term
roadmap for x265.

Let me discuss with the engineering team to figure out when and how we can
add this feature.  Now might not be the best time to commit this patch, as
our rate control lead developer is still working to finish up the new CBR
mode.

Tom


-----Original Message-----
From: x265-devel [mailto:x265-devel-bounces at videolan.org] On Behalf Of
Derek Buitenhuis
Sent: Tuesday, December 23, 2014 12:50 PM
To: x265-devel at videolan.org
Subject: Re: [x265] [PATCH] Basic support for tweaking rate control using
zones

On 12/23/2014 6:03 AM, Deepthi Nandakumar wrote:
> Thanks for your patch. I'm not quite sure any of our regular users need
this as of now. We will keep this on standby though - until any requests
come in.

Zones are fairly popular on e.g. Doom9 and within the the anime community.

I don't really understand the point of keeping it on ice until you get a
request - is it going to hurt?

Cheers,
- Derek
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