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Assign boost to GF bit allocation if past frame had no ARF.

Modify the second-pass code to provide a full golden-frame (GF) bit
allocation boost if the past GF group (GFG) had no alt-ref frame (ARF),
even if the current GFG does contain and ARF.

This mostly has no effect on clips, since switching ARFs on/off between
GFGs is not very common. Has a positive effect on e.g. cheer (+0.45 SSIM
at 600kbps) and football (+0.25 SSIM at 600kbps), particularly at high
bitrates. Has a negative effect (-0.04 SSIM at 300kbps) at pamphlet,
which appears only marginally related to this patch, and crew (-0.1 SSIM
at 700kbps).

Change-Id: I2e32899638b59f857e26efeac18a82e0c0b77089

--- a/vp8/encoder/firstpass.c

+++ b/vp8/encoder/firstpass.c

@@ -1722,14 +1722,15 @@

     cpi->twopass.modified_error_used += gf_group_err;

     // Assign  bits to the arf or gf.

-    {

+    for (i = 0; i <= (cpi->source_alt_ref_pending && cpi->common.frame_type != KEY_FRAME); i++) {

         int Boost;

         int frames_in_section;

         int allocation_chunks;

         int Q = (cpi->oxcf.fixed_q < 0) ? cpi->last_q[INTER_FRAME] : cpi->oxcf.fixed_q;

+        int gf_bits;

         // For ARF frames

-        if (cpi->source_alt_ref_pending)

+        if (cpi->source_alt_ref_pending && i == 0)

         {

             Boost = (cpi->gfu_boost * 3 * GFQ_ADJUSTMENT) / (2 * 100);

             //Boost += (cpi->baseline_gf_interval * 25);

@@ -1768,7 +1769,7 @@

         }

         // Calculate the number of bits to be spent on the gf or arf based on the boost number

-        cpi->twopass.gf_bits = (int)((double)Boost * (cpi->twopass.gf_group_bits / (double)allocation_chunks));

+        gf_bits = (int)((double)Boost * (cpi->twopass.gf_group_bits / (double)allocation_chunks));

         // If the frame that is to be boosted is simpler than the average for

         // the gf/arf group then use an alternative calculation

@@ -1786,9 +1787,9 @@

             alt_gf_bits = (int)((double)Boost * (alt_gf_grp_bits /

                                                  (double)allocation_chunks));

-            if (cpi->twopass.gf_bits > alt_gf_bits)

+            if (gf_bits > alt_gf_bits)

             {

-                cpi->twopass.gf_bits = alt_gf_bits;

+                gf_bits = alt_gf_bits;

             }

         }

         // Else if it is harder than other frames in the group make sure it at

@@ -1801,16 +1802,29 @@

                       mod_frame_err /

                       DOUBLE_DIVIDE_CHECK((double)cpi->twopass.kf_group_error_left));

-            if (alt_gf_bits > cpi->twopass.gf_bits)

+            if (alt_gf_bits > gf_bits)

             {

-                cpi->twopass.gf_bits = alt_gf_bits;

+                gf_bits = alt_gf_bits;

             }

         }

         // Dont allow a negative value for gf_bits

-        if (cpi->twopass.gf_bits < 0)

-            cpi->twopass.gf_bits = 0;

+        if (gf_bits < 0)

+            gf_bits = 0;

+        gf_bits += cpi->min_frame_bandwidth;                     // Add in minimum for a frame

+

+        if (i == 0)

+        {

+            cpi->twopass.gf_bits = gf_bits;

+        }

+        if (i == 1 || (!cpi->source_alt_ref_pending && (cpi->common.frame_type != KEY_FRAME)))

+        {

+            cpi->per_frame_bandwidth = gf_bits;                 // Per frame bit target for this frame

+        }

+    }

+

+    {

         // Adjust KF group bits and error remainin

         cpi->twopass.kf_group_error_left -= gf_group_err;

         cpi->twopass.kf_group_bits -= cpi->twopass.gf_group_bits;

@@ -1825,7 +1839,7 @@

         else

             cpi->twopass.gf_group_error_left = gf_group_err;

-        cpi->twopass.gf_group_bits -= cpi->twopass.gf_bits;

+        cpi->twopass.gf_group_bits -= cpi->twopass.gf_bits - cpi->min_frame_bandwidth;

         if (cpi->twopass.gf_group_bits < 0)

             cpi->twopass.gf_group_bits = 0;

@@ -1841,15 +1855,8 @@

         }

         else

             cpi->twopass.mid_gf_extra_bits = 0;

-

-        cpi->twopass.gf_bits += cpi->min_frame_bandwidth;                                              // Add in minimum for a frame

     }

-    if (!cpi->source_alt_ref_pending && (cpi->common.frame_type != KEY_FRAME))                  // Normal GF and not a KF

-    {

-        cpi->per_frame_bandwidth = cpi->twopass.gf_bits;                                               // Per frame bit target for this frame

-    }

-

     // Adjustment to estimate_max_q based on a measure of complexity of the section

     if (cpi->common.frame_type != KEY_FRAME)

     {

@@ -1998,22 +2005,10 @@

         if (cpi->source_alt_ref_pending && (cpi->common.frame_type != KEY_FRAME))

         {

             // Assign a standard frames worth of bits from those allocated to the GF group

+            int bak = cpi->per_frame_bandwidth;

             vpx_memcpy(&this_frame_copy, &this_frame, sizeof(this_frame));

             assign_std_frame_bits(cpi, &this_frame_copy);

-

-            // If appropriate (we are switching into ARF active but it was not previously active) apply a boost for the gf at the start of the group.

-            //if ( !cpi->source_alt_ref_active && (cpi->gfu_boost > 150) )

-            if (FALSE)

-            {

-                int extra_bits;

-                int pct_extra = (cpi->gfu_boost - 100) / 50;

-

-                pct_extra = (pct_extra > 20) ? 20 : pct_extra;

-

-                extra_bits = (cpi->twopass.gf_group_bits * pct_extra) / 100;

-                cpi->twopass.gf_group_bits -= extra_bits;

-                cpi->per_frame_bandwidth += extra_bits;

-            }

+            cpi->per_frame_bandwidth = bak;

         }

     }

-- 

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