Separate frame context index for GOP layers

Use separate frame context index to code frames at different layers.
The maximum index cap is set as 3. This improves the compression
performance of multi-layer ARF by 0.15% across the test sets.

The overall coding gains from multi-layer ARF are

         avg PSNR       ovarall PSNR        SSIM
lowres   -3.9%            -3.7%            -3.2%
midres   -3.5%            -3.2%            -2.3%
nflx2k   -4.3%            -4.6%            -3.0%

Change-Id: I8a0b345fdd47823c018544a6b4748753faf89dc1

diff --git a/vp9/encoder/vp9_encoder.c b/vp9/encoder/vp9_encoder.c
index 6cece62b48d02667110b71b634a2b249a9794a5b..69ab0445c9d7ad1ced5c70f896c1ca17ef1a53a0 100644 (file)
--- a/vp9/encoder/vp9_encoder.c
+++ b/vp9/encoder/vp9_encoder.c
@@ -780,6 +780,7 @@ void vp9_set_high_precision_mv(VP9_COMP *cpi, int allow_high_precision_mv) {
 
 static void setup_frame(VP9_COMP *cpi) {
   VP9_COMMON *const cm = &cpi->common;
+  GF_GROUP *const gf_group = &cpi->twopass.gf_group;
   // Set up entropy context depending on frame type. The decoder mandates
   // the use of the default context, index 0, for keyframes and inter
   // frames where the error_resilient_mode or intra_only flag is set. For
@@ -791,6 +792,13 @@ static void setup_frame(VP9_COMP *cpi) {
     if (!cpi->use_svc) cm->frame_context_idx = cpi->refresh_alt_ref_frame;
   }
 
+  // TODO(jingning): Overwrite the frame_context_idx index in multi-layer ARF
+  // case. Need some further investigation on if we could apply this to single
+  // layer ARF case as well.
+  if (cpi->multi_layer_arf && !cpi->use_svc)
+    cm->frame_context_idx = clamp(gf_group->layer_depth[gf_group->index] - 1, 0,
+                                  FRAME_CONTEXTS - 1);
+
   if (cm->frame_type == KEY_FRAME) {
     cpi->refresh_golden_frame = 1;
     cpi->refresh_alt_ref_frame = 1;

diff --git a/vp9/encoder/vp9_firstpass.c b/vp9/encoder/vp9_firstpass.c
index 1f95bc6d5c05d7294d58b63eeac2dcb37256099c..87ab8eb844d37571aec84e485e3d10d32c6a9677 100644 (file)
--- a/vp9/encoder/vp9_firstpass.c
+++ b/vp9/encoder/vp9_firstpass.c
@@ -2413,6 +2413,7 @@ static int define_gf_group_structure(VP9_COMP *cpi) {
     }
     gf_group->arf_update_idx[frame_index] = arf_buffer_indices[0];
     gf_group->arf_ref_idx[frame_index] = arf_buffer_indices[0];
+    gf_group->layer_depth[frame_index] = MAX_ARF_LAYERS - 1;
   }
 
   ++frame_index;