shithub: libvpx

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vp9-svc: Allow second temporal reference for next highest layer.

When inter-layer prediction is disabled on INTER frames, allow
for next highest resolution to have second temporal reference.
Current code allowed for only top/highest spatial layer.

Change-Id: I102137273e3e4d57512a13d95e8ccb9c5b0a7b4b

--- a/vp9/encoder/vp9_ratectrl.c

+++ b/vp9/encoder/vp9_ratectrl.c

@@ -1879,8 +1879,11 @@

     if (svc->layer_context[svc->temporal_layer_id].is_key_frame) {

       // On key frame we update the buffer index used for long term reference.

       // Use the alt_ref since it is not used or updated on key frames.

+      int index = svc->spatial_layer_id;

       cpi->ext_refresh_alt_ref_frame = 1;

-      cpi->alt_fb_idx = svc->buffer_longterm_ref.idx;

+      if (svc->number_spatial_layers == 3) index = svc->spatial_layer_id - 1;

+      assert(index >= 0);

+      cpi->alt_fb_idx = svc->buffer_longterm_ref[index].idx;

     } else if (rc->frames_till_gf_update_due == 0) {

       // Set perdiod of next update. Make it a multiple of 10, as the cyclic

       // refresh is typically ~10%, and we'd like the update to happen after

--- a/vp9/encoder/vp9_svc_layercontext.c

+++ b/vp9/encoder/vp9_svc_layercontext.c

@@ -62,8 +62,10 @@

   }

   svc->max_consec_drop = INT_MAX;

-  svc->buffer_longterm_ref.idx = 7;

-  svc->buffer_longterm_ref.is_used = 0;

+  svc->buffer_longterm_ref[1].idx = 7;

+  svc->buffer_longterm_ref[0].idx = 6;

+  svc->buffer_longterm_ref[1].is_used = 0;

+  svc->buffer_longterm_ref[0].is_used = 0;

   if (cpi->oxcf.error_resilient_mode == 0 && cpi->oxcf.pass == 2) {

     if (vpx_realloc_frame_buffer(&cpi->svc.empty_frame.img, SMALL_FRAME_WIDTH,

@@ -714,10 +716,14 @@

     }

   }

-  if (cpi->lst_fb_idx == svc->buffer_longterm_ref.idx ||

-      cpi->gld_fb_idx == svc->buffer_longterm_ref.idx ||

-      cpi->alt_fb_idx == svc->buffer_longterm_ref.idx)

-    svc->buffer_longterm_ref.is_used = 1;

+  if (cpi->lst_fb_idx == svc->buffer_longterm_ref[0].idx ||

+      cpi->gld_fb_idx == svc->buffer_longterm_ref[0].idx ||

+      cpi->alt_fb_idx == svc->buffer_longterm_ref[0].idx)

+    svc->buffer_longterm_ref[0].is_used = 1;

+  if (cpi->lst_fb_idx == svc->buffer_longterm_ref[1].idx ||

+      cpi->gld_fb_idx == svc->buffer_longterm_ref[1].idx ||

+      cpi->alt_fb_idx == svc->buffer_longterm_ref[1].idx)

+    svc->buffer_longterm_ref[1].is_used = 1;

   // For the fixed (non-flexible/bypass) SVC mode:

   // If long term temporal reference is enabled at the sequence level

@@ -725,21 +731,25 @@

   // we can use golden as a second temporal reference

   // (since the spatial/inter-layer reference is disabled).

   // We check that the fb_idx for this reference (buffer_longterm_ref.idx) is

-  // unused (slot 7 should be available for 3-3 layer system).

+  // unused (slot 7 and 6 should be available for 3-3 layer system).

   // For now usage of this second temporal reference will only be used for

-  // highest spatial layer.

+  // highest and next to highest spatial layer (i.e., top and middle layer for

+  // 3 spatial layers).

   svc->use_longterm_ref_current_layer = 0;

-  if (svc->use_longterm_ref && !svc->buffer_longterm_ref.is_used &&

+  if (svc->use_longterm_ref && !svc->buffer_longterm_ref[0].is_used &&

+      !svc->buffer_longterm_ref[1].is_used &&

       svc->temporal_layering_mode != VP9E_TEMPORAL_LAYERING_MODE_BYPASS &&

       svc->disable_inter_layer_pred != INTER_LAYER_PRED_ON &&

       svc->number_spatial_layers <= 3 && svc->number_temporal_layers <= 3 &&

-      svc->spatial_layer_id == svc->number_spatial_layers - 1) {

+      svc->spatial_layer_id >= svc->number_spatial_layers - 2) {

     // Enable the second (long-term) temporal reference at the frame-level.

     svc->use_longterm_ref_current_layer = 1;

     // Only used for prediction for on non-key superframes.

     if (!svc->layer_context[svc->temporal_layer_id].is_key_frame) {

       // Use golden for this reference which will be used for prediction.

-      cpi->gld_fb_idx = svc->buffer_longterm_ref.idx;

+      int index = svc->spatial_layer_id;

+      if (svc->number_spatial_layers == 3) index = svc->spatial_layer_id - 1;

+      cpi->gld_fb_idx = svc->buffer_longterm_ref[index].idx;

       // Enable prediction off LAST (last reference) and golden (which will

       // generally be further behind/long-term reference).

       cpi->ref_frame_flags = VP9_LAST_FLAG | VP9_GOLD_FLAG;

--- a/vp9/encoder/vp9_svc_layercontext.h

+++ b/vp9/encoder/vp9_svc_layercontext.h

@@ -106,7 +106,8 @@

   int use_longterm_ref;

   // Frame level flag to enable second (long term) temporal reference.

   int use_longterm_ref_current_layer;

-  BUFFER_LONGTERM_REF buffer_longterm_ref;

+  // Allow second reference for at most 2 top highest resolution layers.

+  BUFFER_LONGTERM_REF buffer_longterm_ref[2];

   int current_superframe;

   int non_reference_frame;

   int use_base_mv;