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vp9 svc: Reuse scaled_temp in two stage downscaling.

This change eliminates redundant computation in the two stage
downscaling, which saves ~1% encoding time in 3-layer svc encoding.

Change-Id: Ib4b218811b68499a740af1f9b7b5a5445e28d671

--- a/vp9/encoder/vp9_encoder.c

+++ b/vp9/encoder/vp9_encoder.c

@@ -753,6 +753,26 @@

     vpx_internal_error(&cm->error, VPX_CODEC_MEM_ERROR,

                        "Failed to allocate scaled source buffer");

+  // For 1 pass cbr: allocate scaled_frame that may be used as an intermediate

+  // buffer for a 2 stage down-sampling: two stages of 1:2 down-sampling for a

+  // target of 1/4x1/4.

+  if (is_one_pass_cbr_svc(cpi) && !cpi->svc.scaled_temp_is_alloc) {

+    cpi->svc.scaled_temp_is_alloc = 1;

+    if (vpx_realloc_frame_buffer(&cpi->svc.scaled_temp,

+                                 cm->width >> 1,

+                                 cm->height >> 1,

+                                 cm->subsampling_x,

+                                 cm->subsampling_y,

+#if CONFIG_VP9_HIGHBITDEPTH

+                                 cm->use_highbitdepth,

+#endif

+                                 VP9_ENC_BORDER_IN_PIXELS,

+                                 cm->byte_alignment,

+                                 NULL, NULL, NULL))

+      vpx_internal_error(&cpi->common.error, VPX_CODEC_MEM_ERROR,

+                         "Failed to allocate scaled_frame for svc ");

+  }

+

   if (vpx_realloc_frame_buffer(&cpi->scaled_last_source,

                                cm->width, cm->height,

                                cm->subsampling_x, cm->subsampling_y,

@@ -3262,10 +3282,22 @@

       cpi->un_scaled_source->y_height == cm->height << 2 &&

       cpi->svc.scaled_temp.y_width == cm->width << 1 &&

       cpi->svc.scaled_temp.y_height == cm->height << 1) {

+    // For svc, if it is a 1/4x1/4 downscaling, do a two-stage scaling to take

+    // advantage of the 1:2 optimized scaler. In the process, the 1/2x1/2

+    // result will be saved in scaled_temp and might be used later.

     cpi->Source = vp9_svc_twostage_scale(cm,

                                          cpi->un_scaled_source,

                                          &cpi->scaled_source,

                                          &cpi->svc.scaled_temp);

+    cpi->svc.scaled_one_half = 1;

+  } else if (is_one_pass_cbr_svc(cpi) &&

+             cpi->un_scaled_source->y_width == cm->width << 1 &&

+             cpi->un_scaled_source->y_height == cm->height << 1 &&

+             cpi->svc.scaled_one_half) {

+    // If the spatial layer is 1/2x1/2 and the scaling is already done in the

+    // two-stage scaling, use the result directly.

+    cpi->Source = &cpi->svc.scaled_temp;

+    cpi->svc.scaled_one_half = 0;

   } else {

     cpi->Source = vp9_scale_if_required(cm,

                                         cpi->un_scaled_source,

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

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

@@ -33,6 +33,8 @@

   svc->rc_drop_superframe = 0;

   svc->force_zero_mode_spatial_ref = 0;

   svc->use_base_mv = 0;

+  svc->scaled_temp_is_alloc = 0;

+  svc->scaled_one_half = 0;

   svc->current_superframe = 0;

   for (i = 0; i < REF_FRAMES; ++i)

     svc->ref_frame_index[i] = -1;

@@ -42,26 +44,6 @@

     cpi->svc.ext_gld_fb_idx[sl] = 1;

     cpi->svc.ext_alt_fb_idx[sl] = 2;

   }

-

-  // For 1 pass cbr: allocate scaled_frame that may be used as an intermediate

-  // buffer for a 2 stage down-sampling: two stages of 1:2 down-sampling for a

-  // target of 1/4x1/4.

-  if (cpi->oxcf.pass == 0 && cpi->oxcf.rc_mode == VPX_CBR) {

-    if (vpx_realloc_frame_buffer(&cpi->svc.scaled_temp,

-                                 cpi->common.width >> 1,

-                                 cpi->common.height >> 1,

-                                 cpi->common.subsampling_x,

-                                 cpi->common.subsampling_y,

-#if CONFIG_VP9_HIGHBITDEPTH

-                                 cpi->common.use_highbitdepth,

-#endif

-                                 VP9_ENC_BORDER_IN_PIXELS,

-                                 cpi->common.byte_alignment,

-                                 NULL, NULL, NULL))

-      vpx_internal_error(&cpi->common.error, VPX_CODEC_MEM_ERROR,

-                         "Failed to allocate scaled_frame for svc ");

-  }

-

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

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

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

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

@@ -72,6 +72,8 @@

   YV12_BUFFER_CONFIG scaled_frames[MAX_LAG_BUFFERS];

   // Temp buffer used for 2-stage down-sampling, for real-time mode.

   YV12_BUFFER_CONFIG scaled_temp;

+  int scaled_one_half;

+  int scaled_temp_is_alloc;

   // Layer context used for rate control in one pass temporal CBR mode or

   // two pass spatial mode.