Add adaptive midpoint for AQ1.

Make the midpoint variance used in AQ mode 1 segmentation
depend on the overall complexity of the frame in two pass.

Change-Id: I452814ec57f7a32352e41bb250e78066abe952dd

vp9/encoder/vp9_aq_variance.c

diff --git a/vp9/encoder/vp9_aq_variance.c b/vp9/encoder/vp9_aq_variance.c
index df65696..5a9f8a6 100644
--- a/vp9/encoder/vp9_aq_variance.c
+++ b/vp9/encoder/vp9_aq_variance.c
@@ -132,8 +132,13 @@
   return log(var + 1.0);
 }
 
+#define DEFAULT_E_MIDPOINT 10.0;
 int vp9_block_energy(VP9_COMP *cpi, MACROBLOCK *x, BLOCK_SIZE bs) {
   double energy;
-  energy = 0.9 * (vp9_log_block_var(cpi, x, bs) - 10.0);
+  double energy_midpoint;
+  vp9_clear_system_state();
+  energy_midpoint =
+    (cpi->oxcf.pass == 2) ? cpi->twopass.mb_av_energy : DEFAULT_E_MIDPOINT;
+  energy = vp9_log_block_var(cpi, x, bs) - energy_midpoint;
   return clamp((int)round(energy), ENERGY_MIN, ENERGY_MAX);
 }

vp9/encoder/vp9_firstpass.c

diff --git a/vp9/encoder/vp9_firstpass.c b/vp9/encoder/vp9_firstpass.c
index 2e33776..8f14d4c 100644
--- a/vp9/encoder/vp9_firstpass.c
+++ b/vp9/encoder/vp9_firstpass.c
@@ -2457,6 +2457,15 @@
 
   rc->base_frame_target = target_rate;
 
+  {
+    const int num_mbs = (cpi->oxcf.resize_mode != RESIZE_NONE)
+                        ? cpi->initial_mbs : cpi->common.MBs;
+    // The multiplication by 256 reverses a scaling factor of (>> 8)
+    // applied when combining MB error values for the frame.
+    twopass->mb_av_energy =
+      log(((this_frame.intra_error * 256.0) / num_mbs) + 1.0);
+  }
+
   // Update the total stats remaining structure.
   subtract_stats(&twopass->total_left_stats, &this_frame);
 }

vp9/encoder/vp9_firstpass.h

diff --git a/vp9/encoder/vp9_firstpass.h b/vp9/encoder/vp9_firstpass.h
index 0a8f756..a8e4987 100644
--- a/vp9/encoder/vp9_firstpass.h
+++ b/vp9/encoder/vp9_firstpass.h
@@ -96,6 +96,7 @@
   double modified_error_min;
   double modified_error_max;
   double modified_error_left;
+  double mb_av_energy;
 
 #if CONFIG_FP_MB_STATS
   uint8_t *frame_mb_stats_buf;