From b54d5aa91fecaef218c7a5a4174cd0797575b464 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Arttu=20Yl=C3=A4-Outinen?= <arttu.yla-outinen@tut.fi>
Date: Wed, 6 May 2015 14:08:18 +0300
Subject: [PATCH] Select GOP picture weights according to bitrate.

Pictures in same layer have equal weights. At low bitrates, the difference
between low and high layers is greater than at high bitrates.
---
 src/config.c       | 24 ++++++++--------------
 src/config.h       |  3 ---
 src/rate_control.c | 51 +++++++++++++++++++++++++++++++++++++++-------
 3 files changed, 52 insertions(+), 26 deletions(-)

diff --git a/src/config.c b/src/config.c
index 0fbdcdb5..ea51b871 100644
--- a/src/config.c
+++ b/src/config.c
@@ -537,45 +537,37 @@ static int config_parse(config_t *cfg, const char *name, const char *value)
     if(atoi(value) == 8) {
       // GOP
       cfg->gop_len = 8;
-      cfg->gop[0].poc_offset = 8; cfg->gop[0].qp_offset = 1; cfg->gop[0].layer = 1; cfg->gop[0].qp_factor = 0.442;  cfg->gop[0].is_ref = 1;
+      cfg->gop[0].poc_offset = 8; cfg->gop[0].layer = 1; cfg->gop[0].is_ref = 1;
       cfg->gop[0].ref_pos_count = 0;
       cfg->gop[0].ref_neg_count = 3; cfg->gop[0].ref_neg[0] = 8; cfg->gop[0].ref_neg[1] = 12; cfg->gop[0].ref_neg[2] = 16;
-      cfg->gop[0].weight = 6;
 
-      cfg->gop[1].poc_offset = 4; cfg->gop[1].qp_offset = 2; cfg->gop[1].layer = 2; cfg->gop[1].qp_factor = 0.3536; cfg->gop[1].is_ref = 1;
+      cfg->gop[1].poc_offset = 4; cfg->gop[1].layer = 2; cfg->gop[1].is_ref = 1;
       cfg->gop[1].ref_neg_count = 2; cfg->gop[1].ref_neg[0] = 4; cfg->gop[1].ref_neg[1] = 8;
       cfg->gop[1].ref_pos_count = 1; cfg->gop[1].ref_pos[0] = 4;
-      cfg->gop[1].weight = 6;
 
-      cfg->gop[2].poc_offset = 2; cfg->gop[2].qp_offset = 3; cfg->gop[2].layer = 3; cfg->gop[2].qp_factor = 0.3536; cfg->gop[2].is_ref = 1;
+      cfg->gop[2].poc_offset = 2; cfg->gop[2].layer = 3; cfg->gop[2].is_ref = 1;
       cfg->gop[2].ref_neg_count = 2; cfg->gop[2].ref_neg[0] = 2; cfg->gop[2].ref_neg[1] = 6;
       cfg->gop[2].ref_pos_count = 2; cfg->gop[2].ref_pos[0] = 2; cfg->gop[2].ref_pos[1] = 6;
-      cfg->gop[2].weight = 3;
 
-      cfg->gop[3].poc_offset = 1; cfg->gop[3].qp_offset = 4; cfg->gop[3].layer = 4; cfg->gop[3].qp_factor = 0.68;   cfg->gop[3].is_ref = 0;
+      cfg->gop[3].poc_offset = 1; cfg->gop[3].layer = 4; cfg->gop[3].is_ref = 0;
       cfg->gop[3].ref_neg_count = 1; cfg->gop[3].ref_neg[0] = 1;
       cfg->gop[3].ref_pos_count = 3; cfg->gop[3].ref_pos[0] = 1; cfg->gop[3].ref_pos[1] = 3; cfg->gop[3].ref_pos[2] = 7;
-      cfg->gop[3].weight = 2;
 
-      cfg->gop[4].poc_offset = 3; cfg->gop[4].qp_offset = 4; cfg->gop[4].layer = 4; cfg->gop[4].qp_factor = 0.68;   cfg->gop[4].is_ref = 0;
+      cfg->gop[4].poc_offset = 3; cfg->gop[4].layer = 4; cfg->gop[4].is_ref = 0;
       cfg->gop[4].ref_neg_count = 2; cfg->gop[4].ref_neg[0] = 1; cfg->gop[4].ref_neg[1] = 3;
       cfg->gop[4].ref_pos_count = 2; cfg->gop[4].ref_pos[0] = 1; cfg->gop[4].ref_pos[1] = 5;
-      cfg->gop[4].weight = 2;
 
-      cfg->gop[5].poc_offset = 6; cfg->gop[5].qp_offset = 3; cfg->gop[5].layer = 3; cfg->gop[5].qp_factor = 0.3536; cfg->gop[5].is_ref = 1;
+      cfg->gop[5].poc_offset = 6; cfg->gop[5].layer = 3; cfg->gop[5].is_ref = 1;
       cfg->gop[5].ref_neg_count = 2; cfg->gop[5].ref_neg[0] = 2; cfg->gop[5].ref_neg[1] = 6;
       cfg->gop[5].ref_pos_count = 1; cfg->gop[5].ref_pos[0] = 2;
-      cfg->gop[5].weight = 3;
 
-      cfg->gop[6].poc_offset = 5; cfg->gop[6].qp_offset = 4; cfg->gop[6].layer = 4; cfg->gop[6].qp_factor = 0.68;   cfg->gop[6].is_ref = 0;
+      cfg->gop[6].poc_offset = 5; cfg->gop[6].layer = 4;   cfg->gop[6].is_ref = 0;
       cfg->gop[6].ref_neg_count = 2;  cfg->gop[6].ref_neg[0] = 1; cfg->gop[6].ref_neg[1] = 5;
       cfg->gop[6].ref_pos_count = 2; cfg->gop[6].ref_pos[0] = 1; cfg->gop[6].ref_pos[1] = 3;
-      cfg->gop[6].weight = 2;
 
-      cfg->gop[7].poc_offset = 7; cfg->gop[7].qp_offset = 4; cfg->gop[7].layer = 4; cfg->gop[7].qp_factor = 0.68;   cfg->gop[7].is_ref = 0;
+      cfg->gop[7].poc_offset = 7; cfg->gop[7].layer = 4;   cfg->gop[7].is_ref = 0;
       cfg->gop[7].ref_neg_count = 3; cfg->gop[7].ref_neg[0] = 1; cfg->gop[7].ref_neg[1] = 3; cfg->gop[7].ref_neg[2] = 7;
       cfg->gop[7].ref_pos_count = 1; cfg->gop[7].ref_pos[0] = 1;
-      cfg->gop[7].weight = 2;
     } else if(atoi(value)) {
       fprintf(stderr, "Input error: goplen must be 8\n");
       return 0;
diff --git a/src/config.h b/src/config.h
index d2e3655f..20b64741 100644
--- a/src/config.h
+++ b/src/config.h
@@ -29,9 +29,6 @@
 
 
 typedef struct {
-  double qp_factor;
-  int8_t qp_offset;    /*!< \brief QP offset */
-  int8_t weight;
   int8_t poc_offset;   /*!< \brief POC offset */
   int8_t layer;        /*!< \brief Current layer */
   int8_t is_ref;       /*!< \brief Flag if this picture is used as a reference */
diff --git a/src/rate_control.c b/src/rate_control.c
index df190bf0..59418c01 100644
--- a/src/rate_control.c
+++ b/src/rate_control.c
@@ -59,6 +59,47 @@ static void gop_allocate_bits(encoder_state_t * const state)
   state->global->cur_gop_target_bits = MAX(200, gop_target_bits);
 }
 
+/**
+ * Allocate bits for the current picture.
+ * \param state the main encoder state
+ * \return target number of bits
+ */
+double pic_allocate_bits(const encoder_state_t * const state) {
+  const encoder_control_t * const encoder = state->encoder_control;
+
+  if (encoder->cfg->gop_len <= 0) {
+    return state->global->cur_gop_target_bits;
+  }
+
+  const double avg_bits_per_picture =
+    encoder->cfg->target_bitrate / encoder->cfg->framerate;
+  const int pixels_per_picture = encoder->in.width * encoder->in.height;
+  const double avg_bits_per_pixel = avg_bits_per_picture / pixels_per_picture;
+
+  int layer_weights[4];
+#define SET_ARRAY(array, x0, x1, x2, x3) \
+  do { array[0] = x0; array[1] = x1; array[2] = x2; array[3] = x3; } while(0)
+
+  if (avg_bits_per_pixel <= 0.05) {
+    SET_ARRAY(layer_weights, 30, 8, 4, 1);
+  } else if (avg_bits_per_pixel <= 0.1) {
+    SET_ARRAY(layer_weights, 25, 7, 4, 1);
+  } else if (avg_bits_per_pixel <= 0.2) {
+    SET_ARRAY(layer_weights, 20, 6, 4, 1);
+  } else {
+    SET_ARRAY(layer_weights, 15, 5, 4, 1);
+  }
+#undef SET_ARRAY
+
+  const int pic_weight = layer_weights[encoder->cfg->gop[state->global->gop_offset].layer - 1];
+  int sum_weights = 0;
+  for (int i = 0; i < encoder->cfg->gop_len; ++i) {
+    sum_weights += layer_weights[encoder->cfg->gop[i].layer - 1];
+  }
+
+  return state->global->cur_gop_target_bits * pic_weight / sum_weights;
+}
+
 /**
  * \brief Select a lambda value for encoding the next picture
  * \param state the main encoder state
@@ -81,15 +122,11 @@ double select_picture_lambda(encoder_state_t * const state)
       state->previous_encoder_state->global->cur_gop_target_bits;
   }
 
-  const double target_bits_current_picture = (encoder->cfg->gop_len > 0)
-    ? (state->global->cur_gop_target_bits * encoder->cfg->gop[state->global->gop_offset].weight / 22.0)
-    : state->global->cur_gop_target_bits
-  ;
-
   // TODO: take the picture headers into account
   const int pixels_per_picture = encoder->in.width * encoder->in.height;
-  const double target_bits_per_pixel = target_bits_current_picture / pixels_per_picture;
-
+  const double target_bits_current_picture = pic_allocate_bits(state);
+  const double target_bits_per_pixel =
+    target_bits_current_picture / pixels_per_picture;
   const double lambda = 3.2003 * pow(target_bits_per_pixel, -1.367);
   return CLIP(0.1, 10000, lambda);
 }