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vp9: Overshoot detection for skipped base layer.

If scene/slide change is detected on current
superframe and max-q set because of high overshoot:
then if the lower/base spatial layer are skipped on
the current superframe, max-q is forced on the
next encoded base/lower spatial layers.

Change-Id: Id61efda86ee545395012e19476d19845e3932678

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

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

@@ -3832,9 +3832,10 @@

   if (svc->spatial_layer_id == svc->first_spatial_layer_to_encode) {

     svc->high_source_sad_superframe = cpi->rc.high_source_sad;

     // On scene change reset temporal layer pattern to TL0.

-    // TODO(marpan/jianj): Fix this to handle case where base

-    // spatial layers are skipped, in which case we should insert

-    // and reset to spatial layer 0 on scene change.

+    // Note that if the base/lower spatial layers are skipped: instead of

+    // inserting base layer here, we force max-q for the next superframe

+    // with lower spatial layers: this is done in vp9_encodedframe_overshoot()

+    // when max-q is decided for the current layer.

     if (svc->high_source_sad_superframe && svc->temporal_layer_id > 0) {

       // rc->high_source_sad will get reset so copy it to restore it.

       int tmp_high_source_sad = cpi->rc.high_source_sad;

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

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

@@ -3081,21 +3081,27 @@

       cpi->rc.rate_correction_factors[INTER_NORMAL] = rate_correction_factor;

     }

     // For temporal layers, reset the rate control parametes across all

-    // temporal layers.

+    // temporal layers. If the first_spatial_layer_to_encode > 0, then this

+    // superframe has skipped lower base layers. So in this case we should also

+    // reset and force max-q for spatial layers < first_spatial_layer_to_encode.

     if (cpi->use_svc) {

-      int i = 0;

+      int tl = 0;

+      int sl = 0;

       SVC *svc = &cpi->svc;

-      for (i = 0; i < svc->number_temporal_layers; ++i) {

-        const int layer = LAYER_IDS_TO_IDX(svc->spatial_layer_id, i,

-                                           svc->number_temporal_layers);

-        LAYER_CONTEXT *lc = &svc->layer_context[layer];

-        RATE_CONTROL *lrc = &lc->rc;

-        lrc->avg_frame_qindex[INTER_FRAME] = *q;

-        lrc->buffer_level = lrc->optimal_buffer_level;

-        lrc->bits_off_target = lrc->optimal_buffer_level;

-        lrc->rc_1_frame = 0;

-        lrc->rc_2_frame = 0;

-        lrc->rate_correction_factors[INTER_NORMAL] = rate_correction_factor;

+      for (sl = 0; sl < svc->first_spatial_layer_to_encode; ++sl) {

+        for (tl = 0; tl < svc->number_temporal_layers; ++tl) {

+          const int layer =

+              LAYER_IDS_TO_IDX(sl, tl, svc->number_temporal_layers);

+          LAYER_CONTEXT *lc = &svc->layer_context[layer];

+          RATE_CONTROL *lrc = &lc->rc;

+          lrc->avg_frame_qindex[INTER_FRAME] = *q;

+          lrc->buffer_level = lrc->optimal_buffer_level;

+          lrc->bits_off_target = lrc->optimal_buffer_level;

+          lrc->rc_1_frame = 0;

+          lrc->rc_2_frame = 0;

+          lrc->rate_correction_factors[INTER_NORMAL] = rate_correction_factor;

+          lrc->force_max_q = 1;

+        }

       }

     }

     return 1;