[x265] x265-devel Digest, Vol 40, Issue 26

[xuefeng]

hello Min,
Thanks for your reply.

a）
deltaQp = sliceQp - ppsQp
ppsQp is saved in PPS and deltaQp is saved in bitstream.  
In fact, I don't calculate new QP, but calculate a best delta for ppsQP and deltaQp without changing sliceQp.
For example,  deltaQp = 14(cost 4 bits),  sliceQp = 40, and ppsQp = 26
If we set deltaQp = 14 - 14 = 0 ( cost 1 bits)  and ppsQp = 26 + 14 = 40,  sliceQp is still 40.  Then we save 3 - 1 = 2 bits in bitstream for each slice.

b)
I have change QP Range with range extension. Please see this patch.



Regards,
 
             Xuefeng Jiang
 
xuefeng at multicorewareinc.com
 
Message: 3
Date: Wed, 28 Sep 2016 00:02:33 +0800 (CST)
From: chen  <chenm003 at 163.com>
To: "Development for x265" <x265-devel at videolan.org>
Subject: Re: [x265] Optimize slice QP in PPS for x265
Message-ID: <2e196b48.110e.1576c622432.Coremail.chenm003 at 163.com>
Content-Type: text/plain; charset="gbk"
 
Hello Xuefeng,
 
 
Your idea is good, in low bitrate environment, the MV, header are most important part in bitstream.
I take a look your code, it sounds some problems.
 
 
Your calculate correlation between sliceQp and QP Range (it is [0, 51] without range extension), so you will got a constant correlative array for every QP value.
In the final, your algorithm output a QP close to average value of sliceQP.
It is right, just spending more time on compute.
 
 
Regards,
Min
 
 
At 2016-09-27 14:46:14,xuefeng <xuefeng at multicorewareinc.com> wrote:
 
All,
hello!
 
 
x265 set the slice QP in PPS to 26.  Bits can be saved by calculating a closer approximation to the actual slice QP values utilized to encode the bitstream at different quality levels. The delta QP in each slice header is huge especially at low bit rate and quality levels.
 
 
My test command is as follows.
--repeat-headers --hash 1  --input-res 1280x720 --keyint 30 --min-keyint 30 --input "Johnny_1280x720.y4m" --fps 30 --output "test_new.mp4"
 
 
There is a patch in the attachment for this method based on "Changeset: 11587 (d20b78d6d138)".
There is information for x265 coding to see that bitrate goes down.   There is informations for HM decoding to see that MD5 and QP are the same with the method.
 
 
 
 
 
 
Regards,
             Xuefeng Jiang
xuefeng at multicorewareinc.com
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