Enable adaptive rate allocation for multi-layer ARFs

Increase the bit allocation for the intermediate layer ARFs. The
current strategy assigns higher offset to the lower layer ARFs.
The needed budget is borrowed from the base layer ARF allocation.

Change-Id: I16b6e9cce4dab8e73e7b097674d1a8504205026e

2 files changed, 46 insertions, 15 deletions

diff --git a/vp9/encoder/vp9_firstpass.c b/vp9/encoder/vp9_firstpass.c
index c4bb2ef02..5b13e175e 100644
--- a/vp9/encoder/vp9_firstpass.c
+++ b/vp9/encoder/vp9_firstpass.c
@@ -2333,8 +2333,8 @@ static void define_gf_multi_arf_structure(VP9_COMP *cpi) {
   gf_group->brf_src_offset[frame_index] = 0;
 }
 
-static void find_arf_order(GF_GROUP *gf_group, int *layer_depth,
-                           int *index_counter, int depth, int start, int end) {
+static void find_arf_order(GF_GROUP *gf_group, int *index_counter, int depth,
+                           int start, int end) {
   const int mid = (start + end) >> 1;
   const int min_frame_interval = 3;
 
@@ -2345,6 +2345,7 @@ static void find_arf_order(GF_GROUP *gf_group, int *layer_depth,
       gf_group->update_type[*index_counter] = LF_UPDATE;
       gf_group->arf_src_offset[*index_counter] = 0;
       gf_group->rf_level[*index_counter] = INTER_NORMAL;
+      gf_group->layer_depth[*index_counter] = depth;
       ++(*index_counter);
     }
     return;
@@ -2353,20 +2354,21 @@ static void find_arf_order(GF_GROUP *gf_group, int *layer_depth,
   assert(abs(mid - start) >= 1 && abs(mid - end) >= 1);
 
   // Process ARF frame
-  layer_depth[*index_counter] = depth;
+  gf_group->layer_depth[*index_counter] = depth;
   gf_group->update_type[*index_counter] = ARF_UPDATE;
   gf_group->arf_src_offset[*index_counter] = mid - start;
   gf_group->rf_level[*index_counter] = GF_ARF_LOW;
   ++(*index_counter);
 
-  find_arf_order(gf_group, layer_depth, index_counter, depth + 1, start, mid);
+  find_arf_order(gf_group, index_counter, depth + 1, start, mid);
 
   gf_group->update_type[*index_counter] = USE_BUF_FRAME;
   gf_group->arf_src_offset[*index_counter] = 0;
   gf_group->rf_level[*index_counter] = INTER_NORMAL;
+  gf_group->layer_depth[*index_counter] = depth;
   ++(*index_counter);
 
-  find_arf_order(gf_group, layer_depth, index_counter, depth + 1, mid + 1, end);
+  find_arf_order(gf_group, index_counter, depth + 1, mid + 1, end);
 }
 
 static int define_gf_group_structure(VP9_COMP *cpi) {
@@ -2379,7 +2381,6 @@ static int define_gf_group_structure(VP9_COMP *cpi) {
   int mid_frame_idx;
   unsigned char arf_buffer_indices[MAX_ACTIVE_ARFS];
   int normal_frames;
-  int layer_depth[MAX_LAG_BUFFERS];
 
   key_frame = cpi->common.frame_type == KEY_FRAME;
 
@@ -2429,10 +2430,9 @@ static int define_gf_group_structure(VP9_COMP *cpi) {
   }
 
   if (rc->source_alt_ref_pending && cpi->multi_layer_arf) {
-    layer_depth[frame_index] = 1;
+    gf_group->layer_depth[frame_index] = 1;
 
-    find_arf_order(gf_group, layer_depth, &frame_index, 2, 0,
-                   rc->baseline_gf_interval - 1);
+    find_arf_order(gf_group, &frame_index, 2, 0, rc->baseline_gf_interval - 1);
 
     if (rc->source_alt_ref_pending) {
       gf_group->update_type[frame_index] = OVERLAY_UPDATE;
@@ -2442,8 +2442,6 @@ static int define_gf_group_structure(VP9_COMP *cpi) {
       gf_group->rf_level[frame_index] = GF_ARF_STD;
     }
 
-    (void)layer_depth;
-
     return frame_index;
   }
 
@@ -2706,18 +2704,50 @@ static void allocate_gf_group_bits(VP9_COMP *cpi, int64_t gf_group_bits,
 
   if (cpi->multi_layer_arf) {
     int idx;
+    int total_delta = 0;
+    int gap_bits;
     target_frame_size = normal_frame_bits;
     target_frame_size =
         clamp(target_frame_size, 0, VPXMIN(max_bits, (int)total_group_bits));
 
+    gap_bits = VPXMAX(0, gf_arf_bits - target_frame_size);
+
     for (idx = frame_index; idx < gop_frames; ++idx) {
-      if (gf_group->update_type[idx] == USE_BUF_FRAME)
-        gf_group->bit_allocation[idx] = 0;
-      else
-        gf_group->bit_allocation[idx] = target_frame_size;
+      int layer_arf_delta;
+      if (gf_group->update_type[idx] == ARF_UPDATE) {
+        layer_arf_delta = gap_bits >> (gf_group->layer_depth[idx] + 2);
+        total_delta += layer_arf_delta;
+      }
+    }
+
+    total_group_bits -= total_delta;
+
+    if (normal_frames > 1)
+      normal_frame_bits = (int)(total_group_bits / normal_frames);
+    else
+      normal_frame_bits = (int)total_group_bits;
+
+    target_frame_size = normal_frame_bits;
+    target_frame_size =
+        clamp(target_frame_size, 0, VPXMIN(max_bits, (int)total_group_bits));
+
+    // The first layer ARF has its bit allocation assigned.
+    for (idx = frame_index; idx < gop_frames; ++idx) {
+      int layer_arf_delta;
+      switch (gf_group->update_type[idx]) {
+        case ARF_UPDATE:
+          layer_arf_delta = gap_bits >> (gf_group->layer_depth[idx] + 1);
+          gf_group->bit_allocation[idx] = target_frame_size + layer_arf_delta;
+          break;
+        case USE_BUF_FRAME: gf_group->bit_allocation[idx] = 0; break;
+        default: gf_group->bit_allocation[idx] = target_frame_size; break;
+      }
     }
     gf_group->bit_allocation[idx] = 0;
 
+    // Adjust the first layer ARF rate allocation.
+    gf_group->bit_allocation[1] = gf_arf_bits;
+
     for (idx = 0; idx < gop_frames; ++idx)
       if (gf_group->update_type[idx] == LF_UPDATE) break;
     gf_group->first_inter_index = idx;
diff --git a/vp9/encoder/vp9_firstpass.h b/vp9/encoder/vp9_firstpass.h
index e1c882df4..fe02d5b28 100644
--- a/vp9/encoder/vp9_firstpass.h
+++ b/vp9/encoder/vp9_firstpass.h
@@ -138,6 +138,7 @@ typedef struct {
   RATE_FACTOR_LEVEL rf_level[MAX_STATIC_GF_GROUP_LENGTH + 2];
   FRAME_UPDATE_TYPE update_type[MAX_STATIC_GF_GROUP_LENGTH + 2];
   unsigned char arf_src_offset[MAX_STATIC_GF_GROUP_LENGTH + 2];
+  unsigned char layer_depth[MAX_STATIC_GF_GROUP_LENGTH + 2];
   unsigned char arf_update_idx[MAX_STATIC_GF_GROUP_LENGTH + 2];
   unsigned char arf_ref_idx[MAX_STATIC_GF_GROUP_LENGTH + 2];
   unsigned char brf_src_offset[MAX_STATIC_GF_GROUP_LENGTH + 2];