[x265] [PATCH] modified Bframe logic in rateEstimateQscale and rateControlEnd to improve ABR

[aarthi at multicorewareinc.com]

# HG changeset patch
# User Aarthi Thirumalai
# Date 1378916383 -19800
#      Wed Sep 11 21:49:43 2013 +0530
# Node ID e159a2ac38906fd569e4b6dd88271e6ea4d5a87f
# Parent  af8cddab103e87cb7817e4809780a64573d4dad2
modified Bframe logic in rateEstimateQscale and rateControlEnd to improve ABR.

diff -r af8cddab103e -r e159a2ac3890 source/encoder/ratecontrol.cpp
--- a/source/encoder/ratecontrol.cpp	Wed Sep 11 00:03:09 2013 -0500
+++ b/source/encoder/ratecontrol.cpp	Wed Sep 11 21:49:43 2013 +0530
@@ -160,16 +160,19 @@
     {
         /* B-frames don't have independent rate control, but rather get the
          * average QP of the two adjacent P-frames + an offset */
+        TComSlice* prevRefSlice = curFrame->getRefPic(REF_PIC_LIST_0, 0)->getSlice();
+        TComSlice* nextRefSlice = curFrame->getRefPic(REF_PIC_LIST_1, 0)->getSlice();
+        int i0 = prevRefSlice->getSliceType() == I_SLICE;
+        int i1 = nextRefSlice->getSliceType() == I_SLICE;
+        int dt0 = abs(curFrame->getPOC() - prevRefSlice->getPOC());
+        int dt1 = abs(curFrame->getPOC() - nextRefSlice->getPOC());
+        double q0 = prevRefSlice->getSliceQp();
+        double q1 = nextRefSlice->getSliceQp();
 
-        int i0 = curFrame->getRefPic(REF_PIC_LIST_0, 0)->getSlice()->getSliceType() == I_SLICE;
-        int i1 = curFrame->getRefPic(REF_PIC_LIST_1, 0)->getSlice()->getSliceType() == I_SLICE;
-        int dt0 = abs(curFrame->getPOC() - curFrame->getRefPic(REF_PIC_LIST_0, 0)->getPOC());
-        int dt1 = abs(curFrame->getPOC() - curFrame->getRefPic(REF_PIC_LIST_1, 0)->getPOC());
-
-        //TODO:need to figure out this
-        double q0 = curFrame->getRefPic(REF_PIC_LIST_0, 0)->getSlice()->getSliceQp();
-        double q1 = curFrame->getRefPic(REF_PIC_LIST_1, 0)->getSlice()->getSliceQp();
-
+        if (prevRefSlice->getSliceType()  == B_SLICE && prevRefSlice->isReferenced())
+            q0 -= pbOffset / 2;
+        if (nextRefSlice->getSliceType()  == B_SLICE && nextRefSlice->isReferenced())
+            q1 -= pbOffset / 2;
         if (i0 && i1)
             q = (q0 + q1) / 2 + ipOffset;
         else if (i0)
@@ -183,12 +186,8 @@
             q += pbOffset / 2;
         else
             q += pbOffset;
-        
-        double qScale = qp2qScale(q);
 
-        lastQScaleFor[P_SLICE] = lastQScale = qScale/pbFactor;
-
-        return qScale;
+        return qp2qScale(q);
     }
     else
     {
@@ -300,12 +299,14 @@
     if (rateControlMode == X265_RC_ABR)
     {
         if (frameType != B_SLICE)
-            cplxrSum +=  1.1 *bits * qp2qScale(rce->qpaRc) / rce->lastRceq;
+            /* The factor 1.5 is to tune up the actual bits  otherwise the cplxrSum is scaled too low
+             * to improve short term compensation for next frame. */
+            cplxrSum +=  1.5 * bits * qp2qScale(rce->qpaRc) / rce->lastRceq;
         else
         {
             /* Depends on the fact that B-frame's QP is an offset from the following P-frame's.
              * Not perfectly accurate with B-refs, but good enough. */
-            cplxrSum += bits * qp2qScale(rce->qpaRc) / (rce->lastRceq * fabs(0.5 * pbFactor));
+            cplxrSum += bits * qp2qScale(rce->qpaRc) / (rce->lastRceq * fabs(pbFactor));
         }
         cplxrSum *= cbrDecay;
         wantedBitsWindow += frameDuration * bitrate;