aq_cyclicrefresh.c 23.4 KB
Newer Older
Jingning Han's avatar
Jingning Han committed
1 2 3 4 5 6 7 8 9 10 11 12 13
/*
 *  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>

14
#include "vp10/common/seg_common.h"
15
#include "vp10/encoder/aq_cyclicrefresh.h"
16 17
#include "vp10/encoder/ratectrl.h"
#include "vp10/encoder/segmentation.h"
18
#include "vpx_ports/system_state.h"
Jingning Han's avatar
Jingning Han committed
19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568

struct CYCLIC_REFRESH {
  // Percentage of blocks per frame that are targeted as candidates
  // for cyclic refresh.
  int percent_refresh;
  // Maximum q-delta as percentage of base q.
  int max_qdelta_perc;
  // Superblock starting index for cycling through the frame.
  int sb_index;
  // Controls how long block will need to wait to be refreshed again, in
  // excess of the cycle time, i.e., in the case of all zero motion, block
  // will be refreshed every (100/percent_refresh + time_for_refresh) frames.
  int time_for_refresh;
  // Target number of (8x8) blocks that are set for delta-q.
  int target_num_seg_blocks;
  // Actual number of (8x8) blocks that were applied delta-q.
  int actual_num_seg1_blocks;
  int actual_num_seg2_blocks;
  // RD mult. parameters for segment 1.
  int rdmult;
  // Cyclic refresh map.
  signed char *map;
  // Map of the last q a block was coded at.
  uint8_t *last_coded_q_map;
  // Thresholds applied to the projected rate/distortion of the coding block,
  // when deciding whether block should be refreshed.
  int64_t thresh_rate_sb;
  int64_t thresh_dist_sb;
  // Threshold applied to the motion vector (in units of 1/8 pel) of the
  // coding block, when deciding whether block should be refreshed.
  int16_t motion_thresh;
  // Rate target ratio to set q delta.
  double rate_ratio_qdelta;
  // Boost factor for rate target ratio, for segment CR_SEGMENT_ID_BOOST2.
  int rate_boost_fac;
  double low_content_avg;
  int qindex_delta[3];
};

CYCLIC_REFRESH *vp10_cyclic_refresh_alloc(int mi_rows, int mi_cols) {
  size_t last_coded_q_map_size;
  CYCLIC_REFRESH *const cr = vpx_calloc(1, sizeof(*cr));
  if (cr == NULL)
    return NULL;

  cr->map = vpx_calloc(mi_rows * mi_cols, sizeof(*cr->map));
  if (cr->map == NULL) {
    vpx_free(cr);
    return NULL;
  }
  last_coded_q_map_size = mi_rows * mi_cols * sizeof(*cr->last_coded_q_map);
  cr->last_coded_q_map = vpx_malloc(last_coded_q_map_size);
  if (cr->last_coded_q_map == NULL) {
    vpx_free(cr);
    return NULL;
  }
  assert(MAXQ <= 255);
  memset(cr->last_coded_q_map, MAXQ, last_coded_q_map_size);

  return cr;
}

void vp10_cyclic_refresh_free(CYCLIC_REFRESH *cr) {
  vpx_free(cr->map);
  vpx_free(cr->last_coded_q_map);
  vpx_free(cr);
}

// 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 = avg_frame_bandwidth
  // Number of (8x8) blocks in frame = mi_rows * mi_cols;
  const float factor = 0.25;
  const int number_blocks = cm->mi_rows  * cm->mi_cols;
  // The condition below corresponds to turning off at target bitrates:
  // (at 30fps), ~12kbps for CIF, 36kbps for VGA, 100kps for HD/720p.
  // Also turn off at very small frame sizes, to avoid too large fraction of
  // superblocks to be refreshed per frame. Threshold below is less than QCIF.
  if (rc->avg_frame_bandwidth < factor * number_blocks ||
      number_blocks / 64 < 5)
    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(const CYCLIC_REFRESH *cr,
                                const MB_MODE_INFO *mbmi,
                                int64_t rate,
                                int64_t dist,
                                int bsize) {
  MV mv = mbmi->mv[0].as_mv;
  // Reject the block for lower-qp coding if projected distortion
  // is above the threshold, and any of the following is true:
  // 1) mode uses large mv
  // 2) mode is an intra-mode
  // Otherwise accept for refresh.
  if (dist > cr->thresh_dist_sb &&
      (mv.row > cr->motion_thresh || mv.row < -cr->motion_thresh ||
       mv.col > cr->motion_thresh || mv.col < -cr->motion_thresh ||
       !is_inter_block(mbmi)))
    return CR_SEGMENT_ID_BASE;
  else  if (bsize >= BLOCK_16X16 &&
            rate < cr->thresh_rate_sb &&
            is_inter_block(mbmi) &&
            mbmi->mv[0].as_int == 0 &&
            cr->rate_boost_fac > 10)
    // More aggressive delta-q for bigger blocks with zero motion.
    return CR_SEGMENT_ID_BOOST2;
  else
    return CR_SEGMENT_ID_BOOST1;
}

// Compute delta-q for the segment.
static int compute_deltaq(const VP9_COMP *cpi, int q, double rate_factor) {
  const CYCLIC_REFRESH *const cr = cpi->cyclic_refresh;
  const RATE_CONTROL *const rc = &cpi->rc;
  int deltaq = vp10_compute_qdelta_by_rate(rc, cpi->common.frame_type,
                                          q, rate_factor,
                                          cpi->common.bit_depth);
  if ((-deltaq) > cr->max_qdelta_perc * q / 100) {
    deltaq = -cr->max_qdelta_perc * q / 100;
  }
  return deltaq;
}

// For the just encoded frame, estimate the bits, incorporating the delta-q
// from non-base segment. For now ignore effect of multiple segments
// (with different delta-q). Note this function is called in the postencode
// (called from rc_update_rate_correction_factors()).
int vp10_cyclic_refresh_estimate_bits_at_q(const VP9_COMP *cpi,
                                          double correction_factor) {
  const VP9_COMMON *const cm = &cpi->common;
  const CYCLIC_REFRESH *const cr = cpi->cyclic_refresh;
  int estimated_bits;
  int mbs = cm->MBs;
  int num8x8bl = mbs << 2;
  // Weight for non-base segments: use actual number of blocks refreshed in
  // previous/just encoded frame. Note number of blocks here is in 8x8 units.
  double weight_segment1 = (double)cr->actual_num_seg1_blocks / num8x8bl;
  double weight_segment2 = (double)cr->actual_num_seg2_blocks / num8x8bl;
  // Take segment weighted average for estimated bits.
  estimated_bits = (int)((1.0 - weight_segment1 - weight_segment2) *
      vp10_estimate_bits_at_q(cm->frame_type, cm->base_qindex, mbs,
                             correction_factor, cm->bit_depth) +
                             weight_segment1 *
      vp10_estimate_bits_at_q(cm->frame_type,
                             cm->base_qindex + cr->qindex_delta[1], mbs,
                             correction_factor, cm->bit_depth) +
                             weight_segment2 *
      vp10_estimate_bits_at_q(cm->frame_type,
                             cm->base_qindex + cr->qindex_delta[2], mbs,
                             correction_factor, cm->bit_depth));
  return estimated_bits;
}

// Prior to encoding the frame, estimate the bits per mb, for a given q = i and
// a corresponding delta-q (for segment 1). This function is called in the
// rc_regulate_q() to set the base qp index.
// Note: the segment map is set to either 0/CR_SEGMENT_ID_BASE (no refresh) or
// to 1/CR_SEGMENT_ID_BOOST1 (refresh) for each superblock, prior to encoding.
int vp10_cyclic_refresh_rc_bits_per_mb(const VP9_COMP *cpi, int i,
                                      double correction_factor) {
  const VP9_COMMON *const cm = &cpi->common;
  CYCLIC_REFRESH *const cr = cpi->cyclic_refresh;
  int bits_per_mb;
  int num8x8bl = cm->MBs << 2;
  // Weight for segment prior to encoding: take the average of the target
  // number for the frame to be encoded and the actual from the previous frame.
  double weight_segment = (double)((cr->target_num_seg_blocks +
      cr->actual_num_seg1_blocks + cr->actual_num_seg2_blocks) >> 1) /
      num8x8bl;
  // Compute delta-q corresponding to qindex i.
  int deltaq = compute_deltaq(cpi, i, cr->rate_ratio_qdelta);
  // Take segment weighted average for bits per mb.
  bits_per_mb = (int)((1.0 - weight_segment) *
      vp10_rc_bits_per_mb(cm->frame_type, i, correction_factor, cm->bit_depth) +
      weight_segment *
      vp10_rc_bits_per_mb(cm->frame_type, i + deltaq, correction_factor,
                         cm->bit_depth));
  return bits_per_mb;
}

// 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 vp10_cyclic_refresh_update_segment(VP9_COMP *const cpi,
                                       MB_MODE_INFO *const mbmi,
                                       int mi_row, int mi_col,
                                       BLOCK_SIZE bsize,
                                       int64_t rate,
                                       int64_t dist,
                                       int skip) {
  const VP9_COMMON *const cm = &cpi->common;
  CYCLIC_REFRESH *const cr = cpi->cyclic_refresh;
  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;
  const int refresh_this_block = candidate_refresh_aq(cr, mbmi, rate, dist,
                                                      bsize);
  // Default is to not update the refresh map.
  int new_map_value = cr->map[block_index];
  int x = 0; int y = 0;

  // If this block is labeled for refresh, check if we should reset the
  // segment_id.
  if (cyclic_refresh_segment_id_boosted(mbmi->segment_id)) {
    mbmi->segment_id = refresh_this_block;
    // Reset segment_id if will be skipped.
    if (skip)
      mbmi->segment_id = CR_SEGMENT_ID_BASE;
  }

  // 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 (cyclic_refresh_segment_id_boosted(mbmi->segment_id)) {
    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++) {
      int map_offset = block_index + y * cm->mi_cols + x;
      cr->map[map_offset] = new_map_value;
      cpi->segmentation_map[map_offset] = mbmi->segment_id;
      // Inter skip blocks were clearly not coded at the current qindex, so
      // don't update the map for them. For cases where motion is non-zero or
      // the reference frame isn't the previous frame, the previous value in
      // the map for this spatial location is not entirely correct.
      if (!is_inter_block(mbmi) || !skip)
        cr->last_coded_q_map[map_offset] = clamp(
            cm->base_qindex + cr->qindex_delta[mbmi->segment_id], 0, MAXQ);
    }
}

// Update the actual number of blocks that were applied the segment delta q.
void vp10_cyclic_refresh_postencode(VP9_COMP *const cpi) {
  VP9_COMMON *const cm = &cpi->common;
  CYCLIC_REFRESH *const cr = cpi->cyclic_refresh;
  unsigned char *const seg_map = cpi->segmentation_map;
  int mi_row, mi_col;
  cr->actual_num_seg1_blocks = 0;
  cr->actual_num_seg2_blocks = 0;
  for (mi_row = 0; mi_row < cm->mi_rows; mi_row++)
    for (mi_col = 0; mi_col < cm->mi_cols; mi_col++) {
      if (cyclic_refresh_segment_id(
          seg_map[mi_row * cm->mi_cols + mi_col]) == CR_SEGMENT_ID_BOOST1)
        cr->actual_num_seg1_blocks++;
      else if (cyclic_refresh_segment_id(
          seg_map[mi_row * cm->mi_cols + mi_col]) == CR_SEGMENT_ID_BOOST2)
        cr->actual_num_seg2_blocks++;
    }
}

// Set golden frame update interval, for non-svc 1 pass CBR mode.
void vp10_cyclic_refresh_set_golden_update(VP9_COMP *const cpi) {
  RATE_CONTROL *const rc = &cpi->rc;
  CYCLIC_REFRESH *const cr = cpi->cyclic_refresh;
  // Set minimum gf_interval for GF update to a multiple (== 2) of refresh
  // period. Depending on past encoding stats, GF flag may be reset and update
  // may not occur until next baseline_gf_interval.
  if (cr->percent_refresh > 0)
    rc->baseline_gf_interval = 4 * (100 / cr->percent_refresh);
  else
    rc->baseline_gf_interval = 40;
}

// Update some encoding stats (from the just encoded frame). If this frame's
// background has high motion, refresh the golden frame. Otherwise, if the
// golden reference is to be updated check if we should NOT update the golden
// ref.
void vp10_cyclic_refresh_check_golden_update(VP9_COMP *const cpi) {
  VP9_COMMON *const cm = &cpi->common;
  CYCLIC_REFRESH *const cr = cpi->cyclic_refresh;
  int mi_row, mi_col;
  double fraction_low = 0.0;
  int low_content_frame = 0;

  MODE_INFO **mi = cm->mi_grid_visible;
  RATE_CONTROL *const rc = &cpi->rc;
  const int rows = cm->mi_rows, cols = cm->mi_cols;
  int cnt1 = 0, cnt2 = 0;
  int force_gf_refresh = 0;

  for (mi_row = 0; mi_row < rows; mi_row++) {
    for (mi_col = 0; mi_col < cols; mi_col++) {
      int16_t abs_mvr = mi[0]->mbmi.mv[0].as_mv.row >= 0 ?
          mi[0]->mbmi.mv[0].as_mv.row : -1 * mi[0]->mbmi.mv[0].as_mv.row;
      int16_t abs_mvc = mi[0]->mbmi.mv[0].as_mv.col >= 0 ?
          mi[0]->mbmi.mv[0].as_mv.col : -1 * mi[0]->mbmi.mv[0].as_mv.col;

      // Calculate the motion of the background.
      if (abs_mvr <= 16 && abs_mvc <= 16) {
        cnt1++;
        if (abs_mvr == 0 && abs_mvc == 0)
          cnt2++;
      }
      mi++;

      // Accumulate low_content_frame.
      if (cr->map[mi_row * cols + mi_col] < 1)
        low_content_frame++;
    }
    mi += 8;
  }

  // For video conference clips, if the background has high motion in current
  // frame because of the camera movement, set this frame as the golden frame.
  // Use 70% and 5% as the thresholds for golden frame refreshing.
  // Also, force this frame as a golden update frame if this frame will change
  // the resolution (resize_pending != 0).
  if (cpi->resize_pending != 0 ||
     (cnt1 * 10 > (70 * rows * cols) && cnt2 * 20 < cnt1)) {
    vp10_cyclic_refresh_set_golden_update(cpi);
    rc->frames_till_gf_update_due = rc->baseline_gf_interval;

    if (rc->frames_till_gf_update_due > rc->frames_to_key)
      rc->frames_till_gf_update_due = rc->frames_to_key;
    cpi->refresh_golden_frame = 1;
    force_gf_refresh = 1;
  }

  fraction_low =
      (double)low_content_frame / (rows * cols);
  // Update average.
  cr->low_content_avg = (fraction_low + 3 * cr->low_content_avg) / 4;
  if (!force_gf_refresh && cpi->refresh_golden_frame == 1) {
    // Don't update golden reference if the amount of low_content for the
    // current encoded frame is small, or if the recursive average of the
    // low_content over the update interval window falls below threshold.
    if (fraction_low < 0.8 || cr->low_content_avg < 0.7)
      cpi->refresh_golden_frame = 0;
    // Reset for next internal.
    cr->low_content_avg = fraction_low;
  }
}

// Update the segmentation map, and related quantities: cyclic refresh map,
// refresh sb_index, and target number of blocks to be refreshed.
// The map is set to either 0/CR_SEGMENT_ID_BASE (no refresh) or to
// 1/CR_SEGMENT_ID_BOOST1 (refresh) for each superblock.
// Blocks labeled as BOOST1 may later get set to BOOST2 (during the
// encoding of the superblock).
static void cyclic_refresh_update_map(VP9_COMP *const cpi) {
  VP9_COMMON *const cm = &cpi->common;
  CYCLIC_REFRESH *const cr = cpi->cyclic_refresh;
  unsigned char *const seg_map = cpi->segmentation_map;
  int i, block_count, bl_index, sb_rows, sb_cols, sbs_in_frame;
  int xmis, ymis, x, y;
  memset(seg_map, CR_SEGMENT_ID_BASE, cm->mi_rows * cm->mi_cols);
  sb_cols = (cm->mi_cols + MI_BLOCK_SIZE - 1) / MI_BLOCK_SIZE;
  sb_rows = (cm->mi_rows + MI_BLOCK_SIZE - 1) / MI_BLOCK_SIZE;
  sbs_in_frame = sb_cols * sb_rows;
  // Number of target blocks to get the q delta (segment 1).
  block_count = cr->percent_refresh * cm->mi_rows * cm->mi_cols / 100;
  // Set the segmentation map: cycle through the superblocks, 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.
  assert(cr->sb_index < sbs_in_frame);
  i = cr->sb_index;
  cr->target_num_seg_blocks = 0;
  do {
    int sum_map = 0;
    // Get the mi_row/mi_col corresponding to superblock index i.
    int sb_row_index = (i / sb_cols);
    int sb_col_index = i - sb_row_index * sb_cols;
    int mi_row = sb_row_index * MI_BLOCK_SIZE;
    int mi_col = sb_col_index * MI_BLOCK_SIZE;
    int qindex_thresh =
        cpi->oxcf.content == VP9E_CONTENT_SCREEN
            ? vp10_get_qindex(&cm->seg, CR_SEGMENT_ID_BOOST2, cm->base_qindex)
            : 0;
    assert(mi_row >= 0 && mi_row < cm->mi_rows);
    assert(mi_col >= 0 && mi_col < cm->mi_cols);
    bl_index = mi_row * cm->mi_cols + mi_col;
    // Loop through all 8x8 blocks in superblock and update map.
    xmis = MIN(cm->mi_cols - mi_col,
               num_8x8_blocks_wide_lookup[BLOCK_64X64]);
    ymis = MIN(cm->mi_rows - mi_row,
               num_8x8_blocks_high_lookup[BLOCK_64X64]);
    for (y = 0; y < ymis; y++) {
      for (x = 0; x < xmis; x++) {
        const int bl_index2 = bl_index + y * cm->mi_cols + x;
        // If the block 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 block gets coded anything other than ZEROMV.
        if (cr->map[bl_index2] == 0) {
          if (cr->last_coded_q_map[bl_index2] > qindex_thresh)
            sum_map++;
        } else if (cr->map[bl_index2] < 0) {
          cr->map[bl_index2]++;
        }
      }
    }
    // Enforce constant segment over superblock.
    // If segment is at least half of superblock, set to 1.
    if (sum_map >= xmis * ymis / 2) {
      for (y = 0; y < ymis; y++)
        for (x = 0; x < xmis; x++) {
          seg_map[bl_index + y * cm->mi_cols + x] = CR_SEGMENT_ID_BOOST1;
        }
      cr->target_num_seg_blocks += xmis * ymis;
    }
    i++;
    if (i == sbs_in_frame) {
      i = 0;
    }
  } while (cr->target_num_seg_blocks < block_count && i != cr->sb_index);
  cr->sb_index = i;
}

// Set cyclic refresh parameters.
void vp10_cyclic_refresh_update_parameters(VP9_COMP *const cpi) {
  const RATE_CONTROL *const rc = &cpi->rc;
  const VP9_COMMON *const cm = &cpi->common;
  CYCLIC_REFRESH *const cr = cpi->cyclic_refresh;
  cr->percent_refresh = 10;
  cr->max_qdelta_perc = 50;
  cr->time_for_refresh = 0;
  // Use larger delta-qp (increase rate_ratio_qdelta) for first few (~4)
  // periods of the refresh cycle, after a key frame.
  if (rc->frames_since_key <  4 * cr->percent_refresh)
    cr->rate_ratio_qdelta = 3.0;
  else
    cr->rate_ratio_qdelta = 2.0;
  // Adjust some parameters for low resolutions at low bitrates.
  if (cm->width <= 352 &&
      cm->height <= 288 &&
      rc->avg_frame_bandwidth < 3400) {
    cr->motion_thresh = 4;
    cr->rate_boost_fac = 10;
  } else {
    cr->motion_thresh = 32;
    cr->rate_boost_fac = 17;
  }
}

// Setup cyclic background refresh: set delta q and segmentation map.
void vp10_cyclic_refresh_setup(VP9_COMP *const cpi) {
  VP9_COMMON *const cm = &cpi->common;
  const RATE_CONTROL *const rc = &cpi->rc;
  CYCLIC_REFRESH *const cr = cpi->cyclic_refresh;
  struct segmentation *const seg = &cm->seg;
  const int apply_cyclic_refresh  = apply_cyclic_refresh_bitrate(cm, rc);
  if (cm->current_video_frame == 0)
    cr->low_content_avg = 0.0;
  // Don't apply refresh on key frame or enhancement layer frames.
  if (!apply_cyclic_refresh ||
      (cm->frame_type == KEY_FRAME) ||
      (cpi->svc.temporal_layer_id > 0) ||
      (cpi->svc.spatial_layer_id > 0)) {
    // Set segmentation map to 0 and disable.
    unsigned char *const seg_map = cpi->segmentation_map;
    memset(seg_map, 0, cm->mi_rows * cm->mi_cols);
    vp10_disable_segmentation(&cm->seg);
    if (cm->frame_type == KEY_FRAME) {
      memset(cr->last_coded_q_map, MAXQ,
             cm->mi_rows * cm->mi_cols * sizeof(*cr->last_coded_q_map));
      cr->sb_index = 0;
    }
    return;
  } else {
    int qindex_delta = 0;
    int qindex2;
    const double q = vp10_convert_qindex_to_q(cm->base_qindex, cm->bit_depth);
    vpx_clear_system_state();
    // Set rate threshold to some multiple (set to 2 for now) of the target
    // rate (target is given by sb64_target_rate and scaled by 256).
    cr->thresh_rate_sb = ((int64_t)(rc->sb64_target_rate) << 8) << 2;
    // Distortion threshold, quadratic in Q, scale factor to be adjusted.
    // q will not exceed 457, so (q * q) is within 32bit; see:
    // vp10_convert_qindex_to_q(), vp10_ac_quant(), ac_qlookup*[].
    cr->thresh_dist_sb = ((int64_t)(q * q)) << 2;

    // Set up segmentation.
    // Clear down the segment map.
    vp10_enable_segmentation(&cm->seg);
    vp10_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 vp10_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 BASE "Q" feature is disabled so it defaults to the baseline Q.
    vp10_disable_segfeature(seg, CR_SEGMENT_ID_BASE, SEG_LVL_ALT_Q);
    // Use segment BOOST1 for in-frame Q adjustment.
    vp10_enable_segfeature(seg, CR_SEGMENT_ID_BOOST1, SEG_LVL_ALT_Q);
    // Use segment BOOST2 for more aggressive in-frame Q adjustment.
    vp10_enable_segfeature(seg, CR_SEGMENT_ID_BOOST2, SEG_LVL_ALT_Q);

    // Set the q delta for segment BOOST1.
    qindex_delta = compute_deltaq(cpi, cm->base_qindex, cr->rate_ratio_qdelta);
    cr->qindex_delta[1] = qindex_delta;

    // Compute rd-mult for segment BOOST1.
    qindex2 = clamp(cm->base_qindex + cm->y_dc_delta_q + qindex_delta, 0, MAXQ);

    cr->rdmult = vp10_compute_rd_mult(cpi, qindex2);

    vp10_set_segdata(seg, CR_SEGMENT_ID_BOOST1, SEG_LVL_ALT_Q, qindex_delta);

    // Set a more aggressive (higher) q delta for segment BOOST2.
    qindex_delta = compute_deltaq(
        cpi, cm->base_qindex, MIN(CR_MAX_RATE_TARGET_RATIO,
        0.1 * cr->rate_boost_fac * cr->rate_ratio_qdelta));
    cr->qindex_delta[2] = qindex_delta;
    vp10_set_segdata(seg, CR_SEGMENT_ID_BOOST2, SEG_LVL_ALT_Q, qindex_delta);

    // Update the segmentation and refresh map.
    cyclic_refresh_update_map(cpi);
  }
}

int vp10_cyclic_refresh_get_rdmult(const CYCLIC_REFRESH *cr) {
  return cr->rdmult;
}

void vp10_cyclic_refresh_reset_resize(VP9_COMP *const cpi) {
  const VP9_COMMON *const cm = &cpi->common;
  CYCLIC_REFRESH *const cr = cpi->cyclic_refresh;
  memset(cr->map, 0, cm->mi_rows * cm->mi_cols);
  cr->sb_index = 0;
  cpi->refresh_golden_frame = 1;
}