[x265] [PATCH 2 of 2] rc: tune initial predictor values for better frame size predictions in vbv lookahead

[Aarthi Priya Thirumalai]

On Thu, Apr 9, 2015 at 12:09 AM, Steve Borho <steve at borho.org> wrote:

> On 04/08, aarthi at multicorewareinc.com wrote:
> > # HG changeset patch
> > # User Aarthi Thirumalai
> > # Date 1426487738 -19800
> > #      Mon Mar 16 12:05:38 2015 +0530
> > # Node ID b4646bdaf2202748d3a3b159b9bc8e3cfcd272de
> > # Parent  6f159ec858f4eec484d722916c41911e3e4540f9
> > rc: tune initial predictor values for better frame size predictions in
> vbv lookahead
> >
> > an overall improvement in ssim of around .05-.1 db can be seen.
> > Also, improves visual quality at the start of the encode.
> >
> > SteamLocomotiveTrain_2560x1600_60_10bit_crop.yuv --bitrate 9000
> --vbv-bufsize 9000 --strict-cbr
> >
> >        Bitrate         Y PSNR  U PSNR  V PSNR  Global PSNR     SSIM
> SSIM (dB)
> > before  9168.43 39.689  45.096 45.152   41.048         0.93176  11.66
> > after   9106.16  39.864 45.169        45.199    41.194         0.93518
> 11.883
>
> do these pair of commits belong on stable?
>
Yes, they belong on the stable

>
> > diff -r 6f159ec858f4 -r b4646bdaf220 source/encoder/ratecontrol.cpp
> > --- a/source/encoder/ratecontrol.cpp  Tue Mar 31 22:16:21 2015 +0530
> > +++ b/source/encoder/ratecontrol.cpp  Mon Mar 16 12:05:38 2015 +0530
> > @@ -372,12 +372,17 @@
> >      /* Frame Predictors and Row predictors used in vbv */
> >      for (int i = 0; i < 4; i++)
> >      {
> > -        m_pred[i].coeff = 1.5;
> > +        m_pred[i].coeff = 1.0;
> >          m_pred[i].count = 1.0;
> >          m_pred[i].decay = 0.5;
> >          m_pred[i].offset = 0.0;
> >      }
> > -    m_pred[0].coeff = 1.0;
> > +    m_pred[0].coeff = m_pred[3].coeff = 0.75;
> > +    if (m_param->rc.qCompress >= 0.8) // when tuned for grain
> > +    {
> > +        m_pred[1].coeff = 0.75;
> > +        m_pred[0].coeff = m_pred[3].coeff = 0.50;
> > +    }
> >      if (!m_statFileOut && (m_param->rc.bStatWrite ||
> m_param->rc.bStatRead))
> >      {
> >          /* If the user hasn't defined the stat filename, use the
> default value */
> > @@ -1797,8 +1802,11 @@
> >          double pbits = predictSize(&m_pred[m_predType], q,
> (double)m_currentSatd);
> >          if (pbits > rce->frameSizeMaximum)
> >              q *= pbits / rce->frameSizeMaximum;
> > -
> > -        if (!m_isCbr || (m_isAbr && m_currentSatd >= rce->movingAvgSum
> && q <= q0 / 2))
> > +        /* To detect frames that are more complex in SATD costs
> compared to prev window, yet
> > +         * lookahead vbv reduces its qscale by half its value. Be on
> safer side and avoid drastic
> > +         * qscale reductions for frames high in complexity */
> > +        bool mispredCheck = rce->movingAvgSum && m_currentSatd >=
> rce->movingAvgSum && q <= q0 / 2;
> > +        if (!m_isCbr || (m_isAbr && mispredCheck))
> >              q = X265_MAX(q0, q);
> >
> >          if (m_rateFactorMaxIncrement)
> > _______________________________________________
> > x265-devel mailing list
> > x265-devel at videolan.org
> > https://mailman.videolan.org/listinfo/x265-devel
>
> --
> Steve Borho
> _______________________________________________
> x265-devel mailing list
> x265-devel at videolan.org
> https://mailman.videolan.org/listinfo/x265-devel
>
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