[x265] [PATCH] ratecontrol: prevent one layer of non-zero I-slice qp clipping [CHANGES OUTPUT]

[Deepthi Nandakumar]

Santhoshini,

I-slice clipping has been removed only if it is not the first keyframe. I
havent touched the newly introduced logic which clips all concurrent frames
at the beginning.

On Thu, Apr 10, 2014 at 1:54 PM, Santhoshini Sekar <
santhoshini at multicorewareinc.com> wrote:

>
>
>
> On Thu, Apr 10, 2014 at 12:57 PM, <deepthi at multicorewareinc.com> wrote:
>
>> # HG changeset patch
>> # User Deepthi Nandakumar <deepthi at multicorewareinc.com>
>> # Date 1397114813 -19800
>> # Node ID 1c0f1a4ce209badcca1272f87c3917ec69ee1cc7
>> # Parent  83ccf2f1453ffd91c9fd8b84b72e3d3daacba6c6
>> ratecontrol: prevent one layer of non-zero I-slice qp clipping [CHANGES
>> OUTPUT].
>>
>> This seems to have been an error importing RC code from x264. It could be
>> responsible
>> for error reports on I-slices (after POC 0) having much higher QP/low
>> visual quality.
>> Needs review.
>>
>> diff -r 83ccf2f1453f -r 1c0f1a4ce209 source/encoder/ratecontrol.cpp
>> --- a/source/encoder/ratecontrol.cpp    Thu Apr 10 11:17:46 2014 +0530
>> +++ b/source/encoder/ratecontrol.cpp    Thu Apr 10 12:56:53 2014 +0530
>> @@ -554,33 +554,34 @@
>>              q = x265_qp2qScale(accumPQp / accumPNorm);
>>              q /= fabs(param->rc.ipFactor);
>>          }
>> -
>> -        if (param->rc.rateControlMode != X265_RC_CRF)
>> +        else if(framesDone > 0)
>>
>
The above else if part is the only real addition. The remaining stuff is as
is. Diff makes it harder to review the exact change. Pls apply the patch
and you can see the exact change.


>          {
>> -            double lqmin = 0, lqmax = 0;
>> -            if (totalBits == 0 && !isVbv)
>> +            if (param->rc.rateControlMode != X265_RC_CRF)
>>              {
>> -                lqmin = x265_qp2qScale(ABR_INIT_QP_MIN) / lstep;
>> -                lqmax = x265_qp2qScale(ABR_INIT_QP_MAX) * lstep;
>> -                q = Clip3(lqmin, lqmax, q);
>> -            }
>> -            else if (totalBits > 0 || (isVbv && framesDone > 0))
>> -            {
>> -                lqmin = lastQScaleFor[sliceType] / lstep;
>> -                lqmax = lastQScaleFor[sliceType] * lstep;
>> -                if (overflow > 1.1 && framesDone > 3)
>> -                    lqmax *= lstep;
>> -                else if (overflow < 0.9)
>> -                    lqmin /= lstep;
>> -                q = Clip3(lqmin, lqmax, q);
>> +                double lqmin = 0, lqmax = 0;
>> +                if (totalBits == 0 && !isVbv)
>> +                {
>> +                    lqmin = x265_qp2qScale(ABR_INIT_QP_MIN) / lstep;
>> +                    lqmax = x265_qp2qScale(ABR_INIT_QP_MAX) * lstep;
>> +                    q = Clip3(lqmin, lqmax, q);
>> +                }
>>
> The above clipping logic is not present in x264. This was consciously
> introduced only in x265 to clip I slice's qp along with N concurrent
> frames' qp when frame parallelism is enabled. If I slice's clipping is
> removed then we need to remove the above piece of code as well.  Otherwise
> the frames following the I frame might have qp that gets clipped - lower
> than the I frame's qp.
>
>> +                else if (totalBits > 0 || (isVbv && framesDone > 0))
>> +                {
>> +                    lqmin = lastQScaleFor[sliceType] / lstep;
>> +                    lqmax = lastQScaleFor[sliceType] * lstep;
>> +                    if (overflow > 1.1 && framesDone > 3)
>> +                        lqmax *= lstep;
>> +                    else if (overflow < 0.9)
>> +                        lqmin /= lstep;
>> +                    q = Clip3(lqmin, lqmax, q);
>> +                }
>>              }
>>          }
>> -        else
>> +        else if (qCompress != 1 && param->rc.rateControlMode ==
>> X265_RC_CRF)
>>          {
>> -            if (qCompress != 1 && framesDone == 0)
>> -                q = x265_qp2qScale(ABR_INIT_QP) /
>> fabs(param->rc.ipFactor);
>> +            q = x265_qp2qScale(ABR_INIT_QP) / fabs(param->rc.ipFactor);
>>          }
>> -
>> +
>>          q = Clip3(MIN_QPSCALE, MAX_MAX_QPSCALE, q);
>>          qpNoVbv = x265_qScale2qp(q);
>>
>> _______________________________________________
>> x265-devel mailing list
>> x265-devel at videolan.org
>> https://mailman.videolan.org/listinfo/x265-devel
>>
>
>
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