[x265] [PATCH] vbv: tune vbv predictors for better mapping of predicted bits to encoded bits

[Steve Borho]

On 11/17, aarthi at multicorewareinc.com wrote:
> # HG changeset patch
> # User Aarthi Thirumalai
> # Date 1416168026 -19800
> #      Mon Nov 17 01:30:26 2014 +0530
> # Node ID f242fb2114d35441bbfcec4e4b4205567a42ebac
> # Parent  98fb658f3229ab10e808204c265a12e18d71638e
> vbv: tune vbv predictors for better mapping of predicted bits to encoded bits
> 
> diff -r 98fb658f3229 -r f242fb2114d3 source/encoder/ratecontrol.cpp
> --- a/source/encoder/ratecontrol.cpp	Tue Nov 11 19:30:19 2014 +0900
> +++ b/source/encoder/ratecontrol.cpp	Mon Nov 17 01:30:26 2014 +0530
> @@ -404,7 +404,9 @@
>          m_param->bEmitHRDSEI = 0;
>      }
>  
> -    m_isCbr = m_param->rc.rateControlMode == X265_RC_ABR && m_isVbv && !m_2pass && m_param->rc.vbvMaxBitrate <= m_param->rc.bitrate;
> +    m_isCbr = m_param->rc.rateControlMode == X265_RC_ABR && m_isVbv && !m_2pass && m_param->rc.vbvMaxBitrate <= m_param->rc.bitrate;
> +    if (m_isCbr)
> +        m_param->rc.pbFactor = 1.0;

this doesn't really belong here in the rate control code; it over-rides
user configuration of this parameter with no opportunity for them to
prevent it. Perhaps this needs to be part of a '--tune cbr'

>      m_leadingBframes = m_param->bframes;
>      m_bframeBits = 0;
>      m_leadingNoBSatd = 0;
> @@ -494,12 +496,12 @@
>      /* Frame Predictors and Row predictors used in vbv */
>      for (int i = 0; i < 5; i++)
>      {
> -        m_pred[i].coeff = 2.0;
> +        m_pred[i].coeff = 1.5;
>          m_pred[i].count = 1.0;
>          m_pred[i].decay = 0.5;
>          m_pred[i].offset = 0.0;
>      }
> -    m_predBfromP = m_pred[0];
> +    m_pred[0].coeff = 1.0;
>      if (!m_statFileOut && (m_param->rc.bStatWrite || m_param->rc.bStatRead))
>      {
>          /* If the user hasn't defined the stat filename, use the default value */
> @@ -1420,12 +1422,9 @@
>  
>          if (!m_2pass && m_isVbv)
>          {
> -            if (m_leadingBframes > 5)
> -            {
> -                qScale = clipQscale(curFrame, rce, qScale);
> -                m_lastQScaleFor[m_sliceType] = qScale;
> -            }
> -            rce->frameSizePlanned = predictSize(&m_predBfromP, qScale, (double)m_leadingNoBSatd);
> +            qScale = clipQscale(curFrame, rce, qScale);
> +            m_lastQScaleFor[m_sliceType] = qScale;
> +            rce->frameSizePlanned = predictSize(&m_pred[m_sliceType], qScale, (double)m_currentSatd);
>          }
>          else if (m_2pass && m_isVbv)
>          {
> @@ -1725,10 +1724,7 @@
>              {
>                  double frameQ[3];
>                  double curBits;
> -                if (m_sliceType == B_SLICE)
> -                    curBits = predictSize(&m_predBfromP, q, (double)m_currentSatd);
> -                else
> -                    curBits = predictSize(&m_pred[m_sliceType], q, (double)m_currentSatd);
> +                curBits = predictSize(&m_pred[m_sliceType], q, (double)m_currentSatd);
>                  double bufferFillCur = m_bufferFill - curBits;
>                  double targetFill;
>                  double totalDuration = 0;
> @@ -1810,25 +1806,6 @@
>          if (pbits > rce->frameSizeMaximum)
>              q *= pbits / rce->frameSizeMaximum;
>  
> -        // Check B-frame complexity, and use up any bits that would
> -        // overflow before the next P-frame.
> -        if (m_leadingBframes <= 5 && m_sliceType == P_SLICE && !m_singleFrameVbv)
> -        {
> -            int nb = m_leadingBframes;
> -            double bits = predictSize(&m_pred[m_sliceType], q, (double)m_currentSatd);
> -            double bbits = predictSize(&m_predBfromP, q * m_param->rc.pbFactor, (double)m_currentSatd);
> -            double space;
> -            if (bbits > m_bufferRate)
> -                nb = 0;
> -            double pbbits = nb * bbits;
> -
> -            space = m_bufferFill + (1 + nb) * m_bufferRate - m_bufferSize;
> -            if (pbbits < space)
> -                q *= X265_MAX(pbbits / space, bits / (0.5 * m_bufferSize));
> -
> -            q = X265_MAX(q0 / 2, q);
> -        }
> -
>          if (!m_isCbr || (m_isAbr && m_currentSatd >= rce->movingAvgSum && q <= q0 / 2))
>              q = X265_MAX(q0, q);
>  
> @@ -2085,7 +2062,7 @@
>  {
>      if (var < 10)
>          return;
> -    const double range = 1.5;
> +    const double range = 2;
>      double old_coeff = p->coeff / p->count;
>      double new_coeff = bits * q / var;
>      double new_coeff_clipped = Clip3(old_coeff / range, old_coeff * range, new_coeff);
> @@ -2257,16 +2234,6 @@
>  
>      if (m_isVbv)
>      {
> -        if (rce->sliceType == B_SLICE)
> -        {
> -            m_bframeBits += actualBits;
> -            if (rce->bLastMiniGopBFrame)
> -            {
> -                if (rce->bframes != 0)
> -                    updatePredictor(&m_predBfromP, x265_qp2qScale(rce->qpaRc), (double)rce->leadingNoBSatd, (double)m_bframeBits / rce->bframes);
> -                m_bframeBits = 0;
> -            }
> -        }
>          updateVbv(actualBits, rce);
>  
>          if (m_param->bEmitHRDSEI)
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-- 
Steve Borho