vp9_aq_cyclicrefresh.c

/*
 *  Copyright (c) 2014 The WebM project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */

#include <limits.h>
#include <math.h>

#include "vp9/encoder/vp9_aq_cyclicrefresh.h"

#include "vp9/common/vp9_seg_common.h"

#include "vp9/encoder/vp9_ratectrl.h"
#include "vp9/encoder/vp9_rdopt.h"
#include "vp9/encoder/vp9_segmentation.h"


// Check if we should turn off cyclic refresh based on bitrate condition.
static int apply_cyclic_refresh_bitrate(const VP9_COMMON *cm,
                                        const RATE_CONTROL *rc) {
  // Turn off cyclic refresh if bits available per frame is not sufficiently
  // larger than bit cost of segmentation. Segment map bit cost should scale
  // with number of seg blocks, so compare available bits to number of blocks.
  // Average bits available per frame = av_per_frame_bandwidth
  // Number of (8x8) blocks in frame = mi_rows * mi_cols;
  const float factor  = 0.5;
  const int number_blocks = cm->mi_rows  * cm->mi_cols;
  // The condition below corresponds to turning off at target bitrates:
  // ~24kbps for CIF, 72kbps for VGA (at 30fps).
  return rc->av_per_frame_bandwidth >= factor * number_blocks;
}

// Check if this coding block, of size bsize, should be considered for refresh
// (lower-qp coding). Decision can be based on various factors, such as
// size of the coding block (i.e., below min_block size rejected), coding
// mode, and rate/distortion.
static int candidate_refresh_aq(const CYCLIC_REFRESH *cr,
                                const MB_MODE_INFO *mbmi,
                                BLOCK_SIZE bsize, int use_rd) {
  if (use_rd) {
    // If projected rate is below the thresh_rate (well below target,
    // so undershoot expected), accept it for lower-qp coding.
    if (cr->projected_rate_sb < cr->thresh_rate_sb)
      return 1;
    // Otherwise, reject the block for lower-qp coding if any of the following:
    // 1) prediction block size is below min_block_size
    // 2) mode is non-zero mv and projected distortion is above thresh_dist
    // 3) mode is an intra-mode (we may want to allow some of this under
    // another thresh_dist)
    else if (bsize < cr->min_block_size ||
             (mbmi->mv[0].as_int != 0 &&
              cr->projected_dist_sb > cr->thresh_dist_sb) ||
             !is_inter_block(mbmi))
      return 0;
    else
      return 1;
  } else {
    // Rate/distortion not used for update.
    if (bsize < cr->min_block_size ||
        mbmi->mv[0].as_int != 0 ||
        !is_inter_block(mbmi))
      return 0;
    else
      return 1;
  }