Further firstpass.c changes.

base the static image test off a measure of 0,0 motion
instead of the decay accumulator value.

Change "transition to still detection" to compare the
decay rate from successive frames.

Minor tweak to the arf extra boost given based on the
number of frames affected.

Removed unused variable mod_err_per_mb_accumulator.

Change-Id: Idd8360083ad409e45f133ce97dd2488259003e64

vp8/encoder/firstpass.c

@@ -1297,7 +1297,7 @@ static int detect_transition_to_still(
     int frame_interval,
     int still_interval,
     double loop_decay_rate,
-    double decay_accumulator )
+    double last_decay_rate )
 {
     BOOL trans_to_still = FALSE;
 
@@ -1306,12 +1306,12 @@ static int detect_transition_to_still(
     // instead of a clean scene cut.
     if ( (frame_interval > MIN_GF_INTERVAL) &&
          (loop_decay_rate >= 0.999) &&
-         (decay_accumulator < 0.9) )
+         (last_decay_rate < 0.9) )
     {
         int j;
         FIRSTPASS_STATS * position = cpi->twopass.stats_in;
         FIRSTPASS_STATS tmp_next_frame;
-        double decay_rate;
+        double zz_inter;
 
         // Look ahead a few frames to see if static condition
         // persists...
@@ -1320,8 +1320,9 @@ static int detect_transition_to_still(
             if (EOF == input_stats(cpi, &tmp_next_frame))
                 break;
 
-            decay_rate = get_prediction_decay_rate(cpi, &tmp_next_frame);
-            if ( decay_rate < 0.999 )
+            zz_inter =
+                (tmp_next_frame.pcnt_inter - tmp_next_frame.pcnt_motion);
+            if ( zz_inter < 0.999 )
                 break;
         }
         // Reset file position
@@ -1562,9 +1563,8 @@ static int calc_arf_boost(
     *b_boost = boost_score;
 
     arf_boost = (*f_boost + *b_boost);
-    arf_boost += ((b_frames + f_frames) * 25);
-    //if ( arf_boost < ((b_frames + f_frames) * 10) )
-    //     arf_boost = ((b_frames + f_frames) * 10);
+    if ( arf_boost < ((b_frames + f_frames) * 20) )
+         arf_boost = ((b_frames + f_frames) * 20);
 
     return arf_boost;
 }
@@ -1637,13 +1637,14 @@ static void define_gf_group(VP8_COMP *cpi, FIRSTPASS_STATS *this_frame)
 
     double mv_ratio_accumulator = 0.0;
     double decay_accumulator = 1.0;
+    double zero_motion_accumulator = 1.0;
 
     double loop_decay_rate = 1.00;          // Starting decay rate
+    double last_loop_decay_rate = 1.00;
 
     double this_frame_mv_in_out = 0.0;
     double mv_in_out_accumulator = 0.0;
     double abs_mv_in_out_accumulator = 0.0;
-    double mod_err_per_mb_accumulator = 0.0;
 
     int max_bits = frame_max_bits(cpi);     // Max for a single frame
 
@@ -1692,9 +1693,6 @@ static void define_gf_group(VP8_COMP *cpi, FIRSTPASS_STATS *this_frame)
 
         gf_group_err += mod_frame_err;
 
-        mod_err_per_mb_accumulator +=
-            mod_frame_err / DOUBLE_DIVIDE_CHECK((double)cpi->common.MBs);
-
         if (EOF == input_stats(cpi, &next_frame))
             break;
 
@@ -1710,30 +1708,33 @@ static void define_gf_group(VP8_COMP *cpi, FIRSTPASS_STATS *this_frame)
         // Cumulative effect of prediction quality decay
         if ( !flash_detected )
         {
+            last_loop_decay_rate = loop_decay_rate;
             loop_decay_rate = get_prediction_decay_rate(cpi, &next_frame);
             decay_accumulator = decay_accumulator * loop_decay_rate;
-            decay_accumulator =
-                decay_accumulator < 0.1 ? 0.1 : decay_accumulator;
-        }
-        boost_score += decay_accumulator *
-                       calc_frame_boost( cpi, &next_frame,
-                                         this_frame_mv_in_out );
-
-        // Break clause to detect very still sections after motion
-        // For example a staic image after a fade or other transition.
-        if ( detect_transition_to_still( cpi, i, 5,
-                                         loop_decay_rate,
-                                         decay_accumulator ) )
-        {
-            allow_alt_ref = FALSE;
-            boost_score = old_boost_score;
-            break;
+
+            // Monitor for static sections.
+            zero_motion_accumulator *=
+                (next_frame.pcnt_inter - next_frame.pcnt_motion);
+
+            // Break clause to detect very still sections after motion
+            // (for example a staic image after a fade or other transition).
+            if ( detect_transition_to_still( cpi, i, 5, loop_decay_rate,
+                                             last_loop_decay_rate ) )
+            {
+                allow_alt_ref = FALSE;
+                break;
+            }
         }
 
+        // Calculate a boost number for this frame
+        boost_score +=
+            ( decay_accumulator *
+              calc_frame_boost( cpi, &next_frame, this_frame_mv_in_out ) );
+
         // Break out conditions.
         if  (
             // Break at cpi->max_gf_interval unless almost totally static
-            (i >= cpi->max_gf_interval && (decay_accumulator < 0.995)) ||
+            (i >= cpi->max_gf_interval && (zero_motion_accumulator < 0.995)) ||
             (
                 // Dont break out with a very short interval
                 (i > MIN_GF_INTERVAL) &&
@@ -1848,7 +1849,8 @@ static void define_gf_group(VP8_COMP *cpi, FIRSTPASS_STATS *this_frame)
     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++) {
+    for (i = 0; i <= (cpi->source_alt_ref_pending && cpi->common.frame_type != KEY_FRAME); i++)
+    {
         int boost;
         int allocation_chunks;
         int Q = (cpi->oxcf.fixed_q < 0) ? cpi->last_q[INTER_FRAME] : cpi->oxcf.fixed_q;
@@ -2367,6 +2369,7 @@ static void find_next_key_frame(VP8_COMP *cpi, FIRSTPASS_STATS *this_frame)
     FIRSTPASS_STATS *start_position;
 
     double decay_accumulator = 1.0;
+    double zero_motion_accumulator = 1.0;
     double boost_score = 0;
     double old_boost_score = 0.0;
     double loop_decay_rate;
@@ -2568,6 +2571,10 @@ static void find_next_key_frame(VP8_COMP *cpi, FIRSTPASS_STATS *this_frame)
         if (r > RMAX)
             r = RMAX;
 
+        // Monitor for static sections.
+        zero_motion_accumulator *=
+            (next_frame.pcnt_inter - next_frame.pcnt_motion);
+
         // How fast is prediction quality decaying
         loop_decay_rate = get_prediction_decay_rate(cpi, &next_frame);
 
@@ -2652,7 +2659,7 @@ static void find_next_key_frame(VP8_COMP *cpi, FIRSTPASS_STATS *this_frame)
         // spend almost all of the bits on the key frame.
         // cpi->twopass.frames_to_key-1 because key frame itself is taken
         // care of by kf_boost.
-        if ( decay_accumulator >= 0.99 )
+        if ( zero_motion_accumulator >= 0.99 )
         {
             allocation_chunks =
                 ((cpi->twopass.frames_to_key - 1) * 10) + kf_boost;