Changes to coding of dual_pred flag.

Further use of common prediction functions and experiments
with alternate contexts based on mode and reference frame.

For the Derf set using reference frame as basis of context
gives +0.18% Overall Psnr and +0.08 SSIM

Change-Id: Ie7eb76f329f74c9c698614f01ece31de0b6bfc9e

vp8/common/pred_common.c

@@ -39,10 +39,27 @@ unsigned char get_pred_context( VP8_COMMON *const cm,
         break;
 
     case PRED_DUAL:
-        // Second ref not INTRA indicates use of dual pred in neighbour
+        // Context based on use of dual pred flag by neighbours
-        pred_context =
+        //pred_context =
-            ((m - 1)->mbmi.second_ref_frame != INTRA_FRAME) +
+        //    ((m - 1)->mbmi.second_ref_frame != INTRA_FRAME) +
-            ((m - cm->mode_info_stride)->mbmi.second_ref_frame != INTRA_FRAME);
+        //    ((m - cm->mode_info_stride)->mbmi.second_ref_frame != INTRA_FRAME);
+
+        // Context based on mode
+        //if ( m->mbmi.mode == ZEROMV )
+        //    pred_context = 0;
+        //else if ( (m->mbmi.mode == NEARESTMV) || (m->mbmi.mode == NEARMV) )
+        //    pred_context = 1;
+        //else
+        //    pred_context = 2;
+
+        // Context based on reference frame
+        if ( m->mbmi.ref_frame == LAST_FRAME )
+            pred_context = 0;
+        else if ( m->mbmi.ref_frame == GOLDEN_FRAME )
+            pred_context = 1;
+        else
+            pred_context = 2;
+
         break;
 #endif
 
@@ -79,7 +96,9 @@ vp8_prob get_pred_prob( VP8_COMMON *const cm,
         break;
 
     case PRED_DUAL:
-        // Second ref non zero indicates use of dual pred in neighbour
+        // In keeping with convention elsewhre the probability returned is
+        // the probability of a "0" outcome which in this case means the
+        // probability of dual pred off.
         pred_probability = cm->prob_dualpred[pred_context];
         break;
 #endif

vp8/encoder/bitstream.c

@@ -1057,8 +1057,11 @@ static void pack_inter_mode_mvs(VP8_COMP *const cpi)
     int row, col;
 
     int prob_skip_false = 0;
+
 #if CONFIG_DUALPRED
+#if !CONFIG_COMPRED
     int prob_dual_pred[3];
+#endif
 #endif /* CONFIG_DUALPRED */
 
     // Values used in prediction model coding
@@ -1111,6 +1114,18 @@ static void pack_inter_mode_mvs(VP8_COMP *const cpi)
         {
             if (cpi->single_pred_count[i] + cpi->dual_pred_count[i])
             {
+#if CONFIG_COMPRED
+                pc->prob_dualpred[i] = cpi->single_pred_count[i] * 255 /
+                    (cpi->single_pred_count[i] + cpi->dual_pred_count[i]);
+                if (pc->prob_dualpred[i] < 1)
+                    pc->prob_dualpred[i] = 1;
+            }
+            else
+            {
+                pc->prob_dualpred[i] = 128;
+            }
+            vp8_write_literal(w, pc->prob_dualpred[i], 8);
+#else
                 prob_dual_pred[i] = cpi->single_pred_count[i] * 256 /
                     (cpi->single_pred_count[i] + cpi->dual_pred_count[i]);
                 if (prob_dual_pred[i] < 1)
@@ -1123,9 +1138,6 @@ static void pack_inter_mode_mvs(VP8_COMP *const cpi)
                 prob_dual_pred[i] = 128;
             }
             vp8_write_literal(w, prob_dual_pred[i], 8);
-
-#if CONFIG_COMPRED
-            pc->prob_dualpred[i] = prob_dual_pred[i];
 #endif
         }
     }
@@ -1457,7 +1469,9 @@ static void pack_inter_mode_mvs(VP8_COMP *const cpi)
     int prob_skip_false = 0;
 
 #if CONFIG_DUALPRED
+#if !CONFIG_COMPRED
     int prob_dual_pred[3];
+#endif
 #endif /* CONFIG_DUALPRED */
 
     // Values used in prediction model coding
@@ -1507,6 +1521,18 @@ static void pack_inter_mode_mvs(VP8_COMP *const cpi)
         {
             if (cpi->single_pred_count[i] + cpi->dual_pred_count[i])
             {
+#if CONFIG_COMPRED
+                pc->prob_dualpred[i] = cpi->single_pred_count[i] * 255 /
+                    (cpi->single_pred_count[i] + cpi->dual_pred_count[i]);
+                if (pc->prob_dualpred[i] < 1)
+                    pc->prob_dualpred[i] = 1;
+            }
+            else
+            {
+                pc->prob_dualpred[i] = 128;
+            }
+            vp8_write_literal(w, pc->prob_dualpred[i], 8);
+#else
                 prob_dual_pred[i] = cpi->single_pred_count[i] * 256 /
                     (cpi->single_pred_count[i] + cpi->dual_pred_count[i]);
                 if (prob_dual_pred[i] < 1)
@@ -1519,9 +1545,6 @@ static void pack_inter_mode_mvs(VP8_COMP *const cpi)
                 prob_dual_pred[i] = 128;
             }
             vp8_write_literal(w, prob_dual_pred[i], 8);
-
-#if CONFIG_COMPRED
-            pc->prob_dualpred[i] = prob_dual_pred[i];
 #endif
         }
     }

vp8/encoder/encodeframe.c

@@ -1811,13 +1811,21 @@ int vp8cx_encode_inter_macroblock
         if (x->e_mbd.mode_info_context->mbmi.ref_frame &&
             x->e_mbd.mode_info_context->mbmi.mode != SPLITMV)
         {
-            MB_MODE_INFO *t = &x->e_mbd.mode_info_context[-cpi->common.mode_info_stride].mbmi;
+            unsigned char pred_context;
+
+#if CONFIG_COMPRED
+            pred_context = get_pred_context( cm, xd, PRED_DUAL );
+#else
+            MB_MODE_INFO *t = &x->e_mbd.mode_info_context
+                              [-cpi->common.mode_info_stride].mbmi;
             MB_MODE_INFO *l = &x->e_mbd.mode_info_context[-1].mbmi;
-            int cnt = (t->second_ref_frame != INTRA_FRAME) + (l->second_ref_frame != INTRA_FRAME);
+            pred_context = (t->second_ref_frame != INTRA_FRAME) +
-            if (x->e_mbd.mode_info_context->mbmi.second_ref_frame == INTRA_FRAME)
+                           (l->second_ref_frame != INTRA_FRAME);
-                cpi->single_pred_count[cnt]++;
+#endif
+            if (xd->mode_info_context->mbmi.second_ref_frame == INTRA_FRAME)
+                cpi->single_pred_count[pred_context]++;
             else
-                cpi->dual_pred_count[cnt]++;
+                cpi->dual_pred_count[pred_context]++;
         }
 #endif /* CONFIG_DUALPRED */