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

[Adam Marcus]

Thanks for the in depth response Tom. I appreciate that implementing zones might complicate further rate control changes demanded by your customers. Still I think theres many people (myself included) who would find support useful today.

Happy holidays!

Adam

> On 23 Dec 2014, at 20:50, Tom Vaughan <tom.vaughan at multicorewareinc.com> wrote:
> 
> 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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