VP8: For high overshoot, force drop frame and max-out QP.

This allows rate control to react to content of current frame being encoded.
Enabling this feature via the setting: screen_content_mode = 2.

Change-Id: Ib2c6670551d96f4907495d5b7b76bb8c49e673db

vp8/encoder/onyx_if.c

@@ -587,7 +587,8 @@ static void cyclic_background_refresh(VP8_COMP *cpi, int Q, int lf_adjustment)
       // Turn-off under certain conditions (i.e., away from key frame, and if
       // we are at good quality (low Q) and most of the blocks were skipped-encoded
       // in previous frame.
-      if (Q >= 100) {
+      int qp_thresh = (cpi->oxcf.screen_content_mode == 2) ? 80 : 100;
+      if (Q >= qp_thresh) {
         cpi->cyclic_refresh_mode_max_mbs_perframe =
             (cpi->common.mb_rows * cpi->common.mb_cols) / 10;
       } else if (cpi->frames_since_key > 250 &&
@@ -2011,6 +2012,8 @@ struct VP8_COMP* vp8_create_compressor(VP8_CONFIG *oxcf)
     cpi->source_alt_ref_active = 0;
     cpi->common.refresh_alt_ref_frame = 0;
 
+    cpi->force_maxqp = 0;
+
     cpi->b_calculate_psnr = CONFIG_INTERNAL_STATS;
 #if CONFIG_INTERNAL_STATS
     cpi->b_calculate_ssimg = 0;
@@ -4184,7 +4187,10 @@ static void encode_frame_to_data_rate
     */
     if (cpi->cyclic_refresh_mode_enabled)
     {
-      if (cpi->current_layer==0)
+      // Special case for screen_content_mode with golden frame updates.
+      int disable_cr_gf = (cpi->oxcf.screen_content_mode == 2 &&
+                           cm->refresh_golden_frame);
+      if (cpi->current_layer == 0 && cpi->force_maxqp == 0 && !disable_cr_gf)
         cyclic_background_refresh(cpi, Q, 0);
       else
         disable_segmentation(cpi);
@@ -4406,6 +4412,11 @@ static void encode_frame_to_data_rate
         /* transform / motion compensation build reconstruction frame */
         vp8_encode_frame(cpi);
 
+        if (cpi->oxcf.screen_content_mode == 2) {
+          if (vp8_drop_encodedframe_overshoot(cpi, Q))
+            return;
+        }
+
         cpi->projected_frame_size -= vp8_estimate_entropy_savings(cpi);
         cpi->projected_frame_size = (cpi->projected_frame_size > 0) ? cpi->projected_frame_size : 0;
 #endif

vp8/encoder/onyx_int.h

@@ -526,6 +526,8 @@ typedef struct VP8_COMP
     // Measure of average squared difference between source and denoised signal.
     int mse_source_denoised;
 
+    int force_maxqp;
+
 #if CONFIG_MULTITHREAD
     /* multithread data */
     int * mt_current_mb_col;

vp8/encoder/ratectrl.c

@@ -1215,6 +1215,11 @@ int vp8_regulate_q(VP8_COMP *cpi, int target_bits_per_frame)
 {
     int Q = cpi->active_worst_quality;
 
+    if (cpi->force_maxqp == 1) {
+      cpi->active_worst_quality = cpi->worst_quality;
+      return cpi->worst_quality;
+    }
+
     /* Reset Zbin OQ value */
     cpi->mb.zbin_over_quant = 0;
 
@@ -1559,3 +1564,44 @@ int vp8_pick_frame_size(VP8_COMP *cpi)
     }
     return 1;
 }
+// If this just encoded frame (mcomp/transform/quant, but before loopfilter and
+// pack_bitstream) has large overshoot, and was not being encoded close to the
+// max QP, then drop this frame and force next frame to be encoded at max QP.
+// Condition this on 1 pass CBR with screen content mode and frame dropper off.
+// TODO(marpan): Should do this exit condition during the encode_frame
+// (i.e., halfway during the encoding of the frame) to save cycles.
+int vp8_drop_encodedframe_overshoot(VP8_COMP *cpi, int Q) {
+  if (cpi->pass == 0 &&
+      cpi->oxcf.end_usage == USAGE_STREAM_FROM_SERVER &&
+      cpi->drop_frames_allowed == 0 &&
+      cpi->common.frame_type != KEY_FRAME) {
+    // Note: the "projected_frame_size" from encode_frame() only gives estimate
+    // of mode/motion vector rate (in non-rd mode): so below we only require
+    // that projected_frame_size is somewhat greater than per-frame-bandwidth,
+    // but add additional condition with high threshold on prediction residual.
+
+    // QP threshold: only allow dropping if we are not close to qp_max.
+    int thresh_qp = 3 * cpi->worst_quality >> 2;
+    // Rate threshold, in bytes.
+    int thresh_rate = 2 * (cpi->av_per_frame_bandwidth >> 3);
+    // Threshold for the average (over all macroblocks) of the pixel-sum
+    // residual error over 16x16 block. Should add QP dependence on threshold?
+    int thresh_pred_err_mb = (256 << 4);
+    int pred_err_mb = cpi->mb.prediction_error / cpi->common.MBs;
+    if (Q < thresh_qp &&
+        cpi->projected_frame_size > thresh_rate &&
+        pred_err_mb > thresh_pred_err_mb) {
+      // Drop this frame: advance frame counters, and set force_maxqp flag.
+      cpi->common.current_video_frame++;
+      cpi->frames_since_key++;
+      // Flag to indicate we will force next frame to be encoded at max QP.
+      cpi->force_maxqp = 1;
+      return 1;
+    } else {
+      cpi->force_maxqp = 0;
+      return 0;
+    }
+    return 0;
+  }
+  return 0;
+}

vp8/encoder/ratectrl.h

@@ -30,6 +30,8 @@ extern void vp8_compute_frame_size_bounds(VP8_COMP *cpi, int *frame_under_shoot_
 /* return of 0 means drop frame */
 extern int vp8_pick_frame_size(VP8_COMP *cpi);
 
+extern int vp8_drop_encodedframe_overshoot(VP8_COMP *cpi, int Q);
+
 #ifdef __cplusplus
 }  // extern "C"
 #endif

vp8/vp8_cx_iface.c

@@ -199,7 +199,7 @@ static vpx_codec_err_t validate_config(vpx_codec_alg_priv_t      *ctx,
     RANGE_CHECK_HI(vp8_cfg, arnr_strength,   6);
     RANGE_CHECK(vp8_cfg, arnr_type,       1, 3);
     RANGE_CHECK(vp8_cfg, cq_level, 0, 63);
-    RANGE_CHECK_BOOL(vp8_cfg, screen_content_mode);
+    RANGE_CHECK_HI(vp8_cfg, screen_content_mode, 2);
     if (finalize && (cfg->rc_end_usage == VPX_CQ || cfg->rc_end_usage == VPX_Q))
         RANGE_CHECK(vp8_cfg, cq_level,
                     cfg->rc_min_quantizer, cfg->rc_max_quantizer);

vpx/vp8cx.h

@@ -326,6 +326,8 @@ enum vp8e_enc_control_id {
   VP8E_SET_TEMPORAL_LAYER_ID,
 
   /*!\brief Codec control function to set encoder screen content mode.
+   *
+   * 0: off, 1: On, 2: On with more aggressive rate control.
    *
    * Supported in codecs: VP8
    */