vp9/encoder/vp9_craq.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_craq.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(VP9_COMP *const cpi) {
  // 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;
  float factor  = 0.5;
  int number_blocks = cpi->common.mi_rows  * cpi->common.mi_cols;
  // The condition below corresponds to turning off at target bitrates:
  // ~24kbps for CIF, 72kbps for VGA (at 30fps).
  if (cpi->rc.av_per_frame_bandwidth < factor * number_blocks)
    return 0;
  else
    return 1;
}

// 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(VP9_COMP *const cpi,
                                MODE_INFO *const mi,
                                int bsize,
                                int use_rd) {
  CYCLIC_REFRESH *const cr = &cpi->cyclic_refresh;
  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) ||
        (mi->mbmi.mv[0].as_int != 0 &&
            cr->projected_dist_sb > cr->thresh_dist_sb) ||
            !is_inter_block(&mi->mbmi))
      return 0;
    else
      return 1;
  } else {
    // Rate/distortion not used for update.
    if ((bsize < cr->min_block_size) ||
      (mi->mbmi.mv[0].as_int != 0) ||
      !is_inter_block(&mi->mbmi))
      return 0;
    else
      return 1;
  }
}

// Prior to coding a given prediction block, of size bsize at (mi_row, mi_col),
// check if we should reset the segment_id, and update the cyclic_refresh map
// and segmentation map.
void vp9_update_segment_aq(VP9_COMP *const cpi,
                           MODE_INFO *const mi,
                           int mi_row,
                           int mi_col,
                           int bsize,
                           int use_rd) {
  CYCLIC_REFRESH *const cr = &cpi->cyclic_refresh;
  VP9_COMMON *const cm = &cpi->common;
  const int bw = num_8x8_blocks_wide_lookup[bsize];
  const int bh = num_8x8_blocks_high_lookup[bsize];
  const int xmis = MIN(cm->mi_cols - mi_col, bw);
  const int ymis = MIN(cm->mi_rows - mi_row, bh);
  const int block_index = mi_row * cm->mi_cols + mi_col;
  // Default is to not update the refresh map.
  int new_map_value = cr->map[block_index];
  int x = 0; int y = 0;
  int current_segment = mi->mbmi.segment_id;
  int refresh_this_block = candidate_refresh_aq(cpi, mi, bsize, use_rd);
  // Check if we should reset the segment_id for this block.
  if (current_segment && !refresh_this_block)
    mi->mbmi.segment_id = 0;

  // Update the cyclic refresh map, to be used for setting segmentation map
  // for the next frame. If the block  will be refreshed this frame, mark it
  // as clean. The magnitude of the -ve influences how long before we consider
  // it for refresh again.
  if (mi->mbmi.segment_id == 1) {
    new_map_value = -cr->time_for_refresh;
  } else if (refresh_this_block) {
    // Else if it is accepted as candidate for refresh, and has not already
    // been refreshed (marked as 1) then mark it as a candidate for cleanup
    // for future time (marked as 0), otherwise don't update it.
    if (cr->map[block_index] == 1)
      new_map_value = 0;
  } else {
    // Leave it marked as block that is not candidate for refresh.
    new_map_value = 1;
  }
  // Update entries in the cyclic refresh map with new_map_value, and
  // copy mbmi->segment_id into global segmentation map.
  for (y = 0; y < ymis; y++)
    for (x = 0; x < xmis; x++) {
      cr->map[block_index + y * cm->mi_cols + x] = new_map_value;
      cpi->segmentation_map[block_index + y * cm->mi_cols + x] =
          mi->mbmi.segment_id;
    }
  // Keep track of actual number (in units of 8x8) of blocks in segment 1 used
  // for encoding this frame.
  if (mi->mbmi.segment_id)
    cr->num_seg_blocks += xmis * ymis;
}

// Setup cyclic background refresh: set delta q and segmentation map.
void vp9_setup_cyclic_refresh_aq(VP9_COMP *const cpi) {
  VP9_COMMON *const cm = &cpi->common;
  CYCLIC_REFRESH *const cr = &cpi->cyclic_refresh;
  struct segmentation *const seg = &cm->seg;
  unsigned char *seg_map = cpi->segmentation_map;
  int apply_cyclic_refresh  = apply_cyclic_refresh_bitrate(cpi);
  // Don't apply refresh on key frame or enhancement layer frames.
  if (!apply_cyclic_refresh ||
      (cpi->common.frame_type == KEY_FRAME) ||
      (cpi->svc.temporal_layer_id > 0)) {
    // Set segmentation map to 0 and disable.
    vpx_memset(seg_map, 0, cm->mi_rows * cm->mi_cols);
    vp9_disable_segmentation(&cm->seg);
    if (cpi->common.frame_type == KEY_FRAME)
      cr->mb_index = 0;
    return;
  } else {
    int qindex_delta = 0;
    int mbs_in_frame = cm->mi_rows * cm->mi_cols;
    int i, x, y, block_count, bl_index, bl_index2;
    int sum_map, new_value, mi_row, mi_col, xmis, ymis, qindex2;

    // Rate target ratio to set q delta.
    float rate_ratio_qdelta = 2.0;
    vp9_clear_system_state();
    // Some of these parameters may be set via codec-control function later.
    cr->max_mbs_perframe = 10;
    cr->max_qdelta_perc = 50;
    cr->min_block_size = BLOCK_16X16;
    cr->time_for_refresh = 1;
    // Set rate threshold to some fraction of target (and scaled by 256).
    cr->thresh_rate_sb = (cpi->rc.sb64_target_rate * 256) >> 2;
    // Distortion threshold, quadratic in Q, scale factor to be adjusted.
    cr->thresh_dist_sb = 8 * (int)(vp9_convert_qindex_to_q(cm->base_qindex) *
        vp9_convert_qindex_to_q(cm->base_qindex));
    if (cpi->sf.use_nonrd_pick_mode) {
      // May want to be more conservative with thresholds in non-rd mode for now
      // as rate/distortion are derived from model based on prediction residual.
      cr->thresh_rate_sb = (cpi->rc.sb64_target_rate * 256) >> 3;
      cr->thresh_dist_sb = 4 * (int)(vp9_convert_qindex_to_q(cm->base_qindex) *
          vp9_convert_qindex_to_q(cm->base_qindex));
    }

    cr->num_seg_blocks = 0;
    // Set up segmentation.
    // Clear down the segment map.
    vpx_memset(seg_map, 0, cm->mi_rows * cm->mi_cols);
    vp9_enable_segmentation(&cm->seg);
    vp9_clearall_segfeatures(seg);
    // Select delta coding method.
    seg->abs_delta = SEGMENT_DELTADATA;

    // Note: setting temporal_update has no effect, as the seg-map coding method
    // (temporal or spatial) is determined in vp9_choose_segmap_coding_method(),
    // based on the coding cost of each method. For error_resilient mode on the
    // last_frame_seg_map is set to 0, so if temporal coding is used, it is
    // relative to 0 previous map.
    // seg->temporal_update = 0;

    // Segment 0 "Q" feature is disabled so it defaults to the baseline Q.
    vp9_disable_segfeature(seg, 0, SEG_LVL_ALT_Q);
    // Use segment 1 for in-frame Q adjustment.
    vp9_enable_segfeature(seg, 1, SEG_LVL_ALT_Q);

    // Set the q delta for segment 1.
    qindex_delta = vp9_compute_qdelta_by_rate(cpi,
                                              cm->base_qindex,
                                              rate_ratio_qdelta);
    // TODO(marpan): Incorporate the actual-vs-target rate over/undershoot from
    // previous encoded frame.
    if ((-qindex_delta) > cr->max_qdelta_perc * cm->base_qindex / 100) {
      qindex_delta = -cr->max_qdelta_perc * cm->base_qindex / 100;
    }

    // Compute rd-mult for segment 1.
    qindex2 = clamp(cm->base_qindex + cm->y_dc_delta_q + qindex_delta, 0, MAXQ);
    cr->rdmult = vp9_compute_rd_mult(cpi, qindex2);

    vp9_set_segdata(seg, 1, SEG_LVL_ALT_Q, qindex_delta);
    // Number of target macroblocks to get the q delta (segment 1).
    block_count = cr->max_mbs_perframe * mbs_in_frame / 100;
    // Set the segmentation map: cycle through the macroblocks, starting at
    // cr->mb_index, and stopping when either block_count blocks have been found
    // to be refreshed, or we have passed through whole frame.
    // Note the setting of seg_map below is done in two steps (one over 8x8)
    // and then another over SB, in order to keep the value constant over SB.
    // TODO(marpan): Do this in one pass in SB order.
    assert(cr->mb_index < mbs_in_frame);
    i = cr->mb_index;
    do {
      // If the macroblock is as a candidate for clean up then mark it
      // for possible boost/refresh (segment 1). The segment id may get reset to
      // 0 later if the macroblock gets coded anything other than ZEROMV.
      if (cr->map[i] == 0) {
        seg_map[i] = 1;
        block_count--;
      } else if (cr->map[i] < 0) {
        cr->map[i]++;
      }
      i++;
      if (i == mbs_in_frame) {
        i = 0;
      }
    } while (block_count && i != cr->mb_index);
    cr->mb_index = i;
    // Enforce constant segment map over superblock.
    for (mi_row = 0; mi_row < cm->mi_rows; mi_row +=  MI_BLOCK_SIZE)
      for (mi_col = 0; mi_col < cm->mi_cols; mi_col += MI_BLOCK_SIZE) {
        bl_index = mi_row * cm->mi_cols + mi_col;
        xmis = num_8x8_blocks_wide_lookup[BLOCK_64X64];
        ymis = num_8x8_blocks_high_lookup[BLOCK_64X64];
        xmis = MIN(cm->mi_cols - mi_col, xmis);
        ymis = MIN(cm->mi_rows - mi_row, ymis);
        sum_map = 0;
        for (y = 0; y < ymis; y++)
          for (x = 0; x < xmis; x++) {
            bl_index2 = bl_index + y * cm->mi_cols + x;
               sum_map += seg_map[bl_index2];
          }
        new_value = 0;
        // If segment is partial over superblock, reset.
        if (sum_map > 0 && sum_map < xmis * ymis) {
          if (sum_map < xmis * ymis / 2)
            new_value = 0;
          else
            new_value = 1;
          for (y = 0; y < ymis; y++)
            for (x = 0; x < xmis; x++) {
              bl_index2 = bl_index + y * cm->mi_cols + x;
              seg_map[bl_index2] = new_value;
            }
        }
      }
  }
}