libvpx: Add VP9 decoder.

source/libvpx/vp9/encoder/vp9_ratectrl.c

+/*
+ *  Copyright (c) 2010 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 <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <limits.h>
+#include <assert.h>
+
+#include "math.h"
+#include "vp9/common/vp9_alloccommon.h"
+#include "vp9/common/vp9_modecont.h"
+#include "vp9/common/vp9_common.h"
+#include "vp9/encoder/vp9_ratectrl.h"
+#include "vp9/common/vp9_entropymode.h"
+#include "vpx_mem/vpx_mem.h"
+#include "vp9/common/vp9_systemdependent.h"
+#include "vp9/encoder/vp9_encodemv.h"
+#include "vp9/common/vp9_quant_common.h"
+
+#define MIN_BPB_FACTOR          0.005
+#define MAX_BPB_FACTOR          50
+
+#ifdef MODE_STATS
+extern unsigned int y_modes[VP9_YMODES];
+extern unsigned int uv_modes[VP9_UV_MODES];
+extern unsigned int b_modes[B_MODE_COUNT];
+
+extern unsigned int inter_y_modes[MB_MODE_COUNT];
+extern unsigned int inter_uv_modes[VP9_UV_MODES];
+extern unsigned int inter_b_modes[B_MODE_COUNT];
+#endif
+
+// Bits Per MB at different Q (Multiplied by 512)
+#define BPER_MB_NORMBITS    9
+
+// % adjustment to target kf size based on seperation from previous frame
+static const int kf_boost_seperation_adjustment[16] = {
+  30,   40,   50,   55,   60,   65,   70,   75,
+  80,   85,   90,   95,  100,  100,  100,  100,
+};
+
+static const int gf_adjust_table[101] = {
+  100,
+  115, 130, 145, 160, 175, 190, 200, 210, 220, 230,
+  240, 260, 270, 280, 290, 300, 310, 320, 330, 340,
+  350, 360, 370, 380, 390, 400, 400, 400, 400, 400,
+  400, 400, 400, 400, 400, 400, 400, 400, 400, 400,
+  400, 400, 400, 400, 400, 400, 400, 400, 400, 400,
+  400, 400, 400, 400, 400, 400, 400, 400, 400, 400,
+  400, 400, 400, 400, 400, 400, 400, 400, 400, 400,
+  400, 400, 400, 400, 400, 400, 400, 400, 400, 400,
+  400, 400, 400, 400, 400, 400, 400, 400, 400, 400,
+  400, 400, 400, 400, 400, 400, 400, 400, 400, 400,
+};
+
+static const int gf_intra_usage_adjustment[20] = {
+  125, 120, 115, 110, 105, 100,  95,  85,  80,  75,
+  70,  65,  60,  55,  50,  50,  50,  50,  50,  50,
+};
+
+static const int gf_interval_table[101] = {
+  7,
+  7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
+  7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
+  7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
+  8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+  8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+  9, 9, 9, 9, 9, 9, 9, 9, 9, 9,
+  9, 9, 9, 9, 9, 9, 9, 9, 9, 9,
+  10, 10, 10, 10, 10, 10, 10, 10, 10, 10,
+  10, 10, 10, 10, 10, 10, 10, 10, 10, 10,
+  11, 11, 11, 11, 11, 11, 11, 11, 11, 11,
+};
+
+static const unsigned int prior_key_frame_weight[KEY_FRAME_CONTEXT] = { 1, 2, 3, 4, 5 };
+
+// These functions use formulaic calculations to make playing with the
+// quantizer tables easier. If necessary they can be replaced by lookup
+// tables if and when things settle down in the experimental bitstream
+double vp9_convert_qindex_to_q(int qindex) {
+  // Convert the index to a real Q value (scaled down to match old Q values)
+  return (double)vp9_ac_yquant(qindex) / 4.0;
+}
+
+int vp9_gfboost_qadjust(int qindex) {
+  int retval;
+  double q;
+
+  q = vp9_convert_qindex_to_q(qindex);
+  retval = (int)((0.00000828 * q * q * q) +
+                 (-0.0055 * q * q) +
+                 (1.32 * q) + 79.3);
+  return retval;
+}
+
+static int kfboost_qadjust(int qindex) {
+  int retval;
+  double q;
+
+  q = vp9_convert_qindex_to_q(qindex);
+  retval = (int)((0.00000973 * q * q * q) +
+                 (-0.00613 * q * q) +
+                 (1.316 * q) + 121.2);
+  return retval;
+}
+
+int vp9_bits_per_mb(FRAME_TYPE frame_type, int qindex) {
+  if (frame_type == KEY_FRAME)
+    return (int)(4500000 / vp9_convert_qindex_to_q(qindex));
+  else
+    return (int)(2850000 / vp9_convert_qindex_to_q(qindex));
+}
+
+
+void vp9_save_coding_context(VP9_COMP *cpi) {
+  CODING_CONTEXT *const cc = &cpi->coding_context;
+  VP9_COMMON *cm = &cpi->common;
+  MACROBLOCKD *xd = &cpi->mb.e_mbd;
+
+  // Stores a snapshot of key state variables which can subsequently be
+  // restored with a call to vp9_restore_coding_context. These functions are
+  // intended for use in a re-code loop in vp9_compress_frame where the
+  // quantizer value is adjusted between loop iterations.
+
+  cc->nmvc = cm->fc.nmvc;
+  vp9_copy(cc->nmvjointcost,  cpi->mb.nmvjointcost);
+  vp9_copy(cc->nmvcosts,  cpi->mb.nmvcosts);
+  vp9_copy(cc->nmvcosts_hp,  cpi->mb.nmvcosts_hp);
+
+  vp9_copy(cc->vp9_mode_contexts, cm->fc.vp9_mode_contexts);
+
+  vp9_copy(cc->ymode_prob, cm->fc.ymode_prob);
+#if CONFIG_SUPERBLOCKS
+  vp9_copy(cc->sb_ymode_prob, cm->fc.sb_ymode_prob);
+#endif
+  vp9_copy(cc->bmode_prob, cm->fc.bmode_prob);
+  vp9_copy(cc->uv_mode_prob, cm->fc.uv_mode_prob);
+  vp9_copy(cc->i8x8_mode_prob, cm->fc.i8x8_mode_prob);
+  vp9_copy(cc->sub_mv_ref_prob, cm->fc.sub_mv_ref_prob);
+  vp9_copy(cc->mbsplit_prob, cm->fc.mbsplit_prob);
+
+  // Stats
+#ifdef MODE_STATS
+  vp9_copy(cc->y_modes,       y_modes);
+  vp9_copy(cc->uv_modes,      uv_modes);
+  vp9_copy(cc->b_modes,       b_modes);
+  vp9_copy(cc->inter_y_modes,  inter_y_modes);
+  vp9_copy(cc->inter_uv_modes, inter_uv_modes);
+  vp9_copy(cc->inter_b_modes,  inter_b_modes);
+#endif
+
+  vp9_copy(cc->segment_pred_probs, cm->segment_pred_probs);
+  vp9_copy(cc->ref_pred_probs_update, cpi->ref_pred_probs_update);
+  vp9_copy(cc->ref_pred_probs, cm->ref_pred_probs);
+  vp9_copy(cc->prob_comppred, cm->prob_comppred);
+
+  vpx_memcpy(cpi->coding_context.last_frame_seg_map_copy,
+             cm->last_frame_seg_map, (cm->mb_rows * cm->mb_cols));
+
+  vp9_copy(cc->last_ref_lf_deltas, xd->last_ref_lf_deltas);
+  vp9_copy(cc->last_mode_lf_deltas, xd->last_mode_lf_deltas);
+
+  vp9_copy(cc->coef_probs, cm->fc.coef_probs);
+  vp9_copy(cc->hybrid_coef_probs, cm->fc.hybrid_coef_probs);
+  vp9_copy(cc->coef_probs_8x8, cm->fc.coef_probs_8x8);
+  vp9_copy(cc->hybrid_coef_probs_8x8, cm->fc.hybrid_coef_probs_8x8);
+  vp9_copy(cc->coef_probs_16x16, cm->fc.coef_probs_16x16);
+  vp9_copy(cc->hybrid_coef_probs_16x16, cm->fc.hybrid_coef_probs_16x16);
+  vp9_copy(cc->switchable_interp_prob, cm->fc.switchable_interp_prob);
+#if CONFIG_COMP_INTERINTRA_PRED
+  cc->interintra_prob = cm->fc.interintra_prob;
+#endif
+}
+
+void vp9_restore_coding_context(VP9_COMP *cpi) {
+  CODING_CONTEXT *const cc = &cpi->coding_context;
+  VP9_COMMON *cm = &cpi->common;
+  MACROBLOCKD *xd = &cpi->mb.e_mbd;
+
+  // Restore key state variables to the snapshot state stored in the
+  // previous call to vp9_save_coding_context.
+
+  cm->fc.nmvc = cc->nmvc;
+  vp9_copy(cpi->mb.nmvjointcost, cc->nmvjointcost);
+  vp9_copy(cpi->mb.nmvcosts, cc->nmvcosts);
+  vp9_copy(cpi->mb.nmvcosts_hp, cc->nmvcosts_hp);
+
+  vp9_copy(cm->fc.vp9_mode_contexts, cc->vp9_mode_contexts);
+
+  vp9_copy(cm->fc.ymode_prob, cc->ymode_prob);
+#if CONFIG_SUPERBLOCKS
+  vp9_copy(cm->fc.sb_ymode_prob, cc->sb_ymode_prob);
+#endif
+  vp9_copy(cm->fc.bmode_prob, cc->bmode_prob);
+  vp9_copy(cm->fc.i8x8_mode_prob, cc->i8x8_mode_prob);
+  vp9_copy(cm->fc.uv_mode_prob, cc->uv_mode_prob);
+  vp9_copy(cm->fc.sub_mv_ref_prob, cc->sub_mv_ref_prob);
+  vp9_copy(cm->fc.mbsplit_prob, cc->mbsplit_prob);
+
+  // Stats
+#ifdef MODE_STATS
+  vp9_copy(y_modes, cc->y_modes);
+  vp9_copy(uv_modes, cc->uv_modes);
+  vp9_copy(b_modes, cc->b_modes);
+  vp9_copy(inter_y_modes, cc->inter_y_modes);
+  vp9_copy(inter_uv_modes, cc->inter_uv_modes);
+  vp9_copy(inter_b_modes, cc->inter_b_modes);
+#endif
+
+  vp9_copy(cm->segment_pred_probs, cc->segment_pred_probs);
+  vp9_copy(cpi->ref_pred_probs_update, cc->ref_pred_probs_update);
+  vp9_copy(cm->ref_pred_probs, cc->ref_pred_probs);
+  vp9_copy(cm->prob_comppred, cc->prob_comppred);
+
+  vpx_memcpy(cm->last_frame_seg_map,
+             cpi->coding_context.last_frame_seg_map_copy,
+             (cm->mb_rows * cm->mb_cols));
+
+  vp9_copy(xd->last_ref_lf_deltas, cc->last_ref_lf_deltas);
+  vp9_copy(xd->last_mode_lf_deltas, cc->last_mode_lf_deltas);
+
+  vp9_copy(cm->fc.coef_probs, cc->coef_probs);
+  vp9_copy(cm->fc.hybrid_coef_probs, cc->hybrid_coef_probs);
+  vp9_copy(cm->fc.coef_probs_8x8, cc->coef_probs_8x8);
+  vp9_copy(cm->fc.hybrid_coef_probs_8x8, cc->hybrid_coef_probs_8x8);
+  vp9_copy(cm->fc.coef_probs_16x16, cc->coef_probs_16x16);
+  vp9_copy(cm->fc.hybrid_coef_probs_16x16, cc->hybrid_coef_probs_16x16);
+  vp9_copy(cm->fc.switchable_interp_prob, cc->switchable_interp_prob);
+#if CONFIG_COMP_INTERINTRA_PRED
+  cm->fc.interintra_prob = cc->interintra_prob;
+#endif
+}
+
+
+void vp9_setup_key_frame(VP9_COMP *cpi) {
+  VP9_COMMON *cm = &cpi->common;
+  // Setup for Key frame:
+  vp9_default_coef_probs(& cpi->common);
+  vp9_kf_default_bmode_probs(cpi->common.kf_bmode_prob);
+  vp9_init_mbmode_probs(& cpi->common);
+  vp9_default_bmode_probs(cm->fc.bmode_prob);
+
+  vp9_init_mv_probs(& cpi->common);
+
+  // cpi->common.filter_level = 0;      // Reset every key frame.
+  cpi->common.filter_level = cpi->common.base_qindex * 3 / 8;
+
+  // interval before next GF
+  cpi->frames_till_gf_update_due = cpi->baseline_gf_interval;
+
+  cpi->common.refresh_golden_frame = TRUE;
+  cpi->common.refresh_alt_ref_frame = TRUE;
+
+  vp9_init_mode_contexts(&cpi->common);
+  vpx_memcpy(&cpi->common.lfc, &cpi->common.fc, sizeof(cpi->common.fc));
+  vpx_memcpy(&cpi->common.lfc_a, &cpi->common.fc, sizeof(cpi->common.fc));
+
+  vpx_memset(cm->prev_mip, 0,
+    (cm->mb_cols + 1) * (cm->mb_rows + 1)* sizeof(MODE_INFO));
+  vpx_memset(cm->mip, 0,
+    (cm->mb_cols + 1) * (cm->mb_rows + 1)* sizeof(MODE_INFO));
+
+  vp9_update_mode_info_border(cm, cm->mip);
+  vp9_update_mode_info_in_image(cm, cm->mi);
+}
+
+void vp9_setup_inter_frame(VP9_COMP *cpi) {
+  if (cpi->common.refresh_alt_ref_frame) {
+    vpx_memcpy(&cpi->common.fc,
+               &cpi->common.lfc_a,
+               sizeof(cpi->common.fc));
+  } else {
+    vpx_memcpy(&cpi->common.fc,
+               &cpi->common.lfc,
+               sizeof(cpi->common.fc));
+  }
+}
+
+
+static int estimate_bits_at_q(int frame_kind, int Q, int MBs,
+                              double correction_factor) {
+  int Bpm = (int)(.5 + correction_factor * vp9_bits_per_mb(frame_kind, Q));
+
+  /* Attempt to retain reasonable accuracy without overflow. The cutoff is
+   * chosen such that the maximum product of Bpm and MBs fits 31 bits. The
+   * largest Bpm takes 20 bits.
+   */
+  if (MBs > (1 << 11))
+    return (Bpm >> BPER_MB_NORMBITS) * MBs;
+  else
+    return (Bpm * MBs) >> BPER_MB_NORMBITS;
+}
+
+
+static void calc_iframe_target_size(VP9_COMP *cpi) {
+  // boost defaults to half second
+  int target;
+
+  // Clear down mmx registers to allow floating point in what follows
+  vp9_clear_system_state();  // __asm emms;
+
+  // New Two pass RC
+  target = cpi->per_frame_bandwidth;
+
+  if (cpi->oxcf.rc_max_intra_bitrate_pct) {
+    int max_rate = cpi->per_frame_bandwidth
+                 * cpi->oxcf.rc_max_intra_bitrate_pct / 100;
+
+    if (target > max_rate)
+      target = max_rate;
+  }
+
+  cpi->this_frame_target = target;
+
+}
+
+
+//  Do the best we can to define the parameteres for the next GF based
+//  on what information we have available.
+//
+//  In this experimental code only two pass is supported
+//  so we just use the interval determined in the two pass code.
+static void calc_gf_params(VP9_COMP *cpi) {
+  // Set the gf interval
+  cpi->frames_till_gf_update_due = cpi->baseline_gf_interval;
+}
+
+
+static void calc_pframe_target_size(VP9_COMP *cpi) {
+  int min_frame_target;
+
+  min_frame_target = 0;
+
+  min_frame_target = cpi->min_frame_bandwidth;
+
+  if (min_frame_target < (cpi->av_per_frame_bandwidth >> 5))
+    min_frame_target = cpi->av_per_frame_bandwidth >> 5;
+
+
+  // Special alt reference frame case
+  if (cpi->common.refresh_alt_ref_frame) {
+    // Per frame bit target for the alt ref frame
+    cpi->per_frame_bandwidth = cpi->twopass.gf_bits;
+    cpi->this_frame_target = cpi->per_frame_bandwidth;
+  }
+
+  // Normal frames (gf,and inter)
+  else {
+    cpi->this_frame_target = cpi->per_frame_bandwidth;
+  }
+
+  // Sanity check that the total sum of adjustments is not above the maximum allowed
+  // That is that having allowed for KF and GF penalties we have not pushed the
+  // current interframe target to low. If the adjustment we apply here is not capable of recovering
+  // all the extra bits we have spent in the KF or GF then the remainder will have to be recovered over
+  // a longer time span via other buffer / rate control mechanisms.
+  if (cpi->this_frame_target < min_frame_target)
+    cpi->this_frame_target = min_frame_target;
+
+  if (!cpi->common.refresh_alt_ref_frame)
+    // Note the baseline target data rate for this inter frame.
+    cpi->inter_frame_target = cpi->this_frame_target;
+
+  // Adjust target frame size for Golden Frames:
+  if (cpi->frames_till_gf_update_due == 0) {
+    // int Boost = 0;
+    int Q = (cpi->oxcf.fixed_q < 0) ? cpi->last_q[INTER_FRAME] : cpi->oxcf.fixed_q;
+
+    cpi->common.refresh_golden_frame = TRUE;
+
+    calc_gf_params(cpi);
+
+    // If we are using alternate ref instead of gf then do not apply the boost
+    // It will instead be applied to the altref update
+    // Jims modified boost
+    if (!cpi->source_alt_ref_active) {
+      if (cpi->oxcf.fixed_q < 0) {
+        // The spend on the GF is defined in the two pass code
+        // for two pass encodes
+        cpi->this_frame_target = cpi->per_frame_bandwidth;
+      } else
+        cpi->this_frame_target =
+          (estimate_bits_at_q(1, Q, cpi->common.MBs, 1.0)
+           * cpi->last_boost) / 100;
+
+    }
+    // If there is an active ARF at this location use the minimum
+    // bits on this frame even if it is a contructed arf.
+    // The active maximum quantizer insures that an appropriate
+    // number of bits will be spent if needed for contstructed ARFs.
+    else {
+      cpi->this_frame_target = 0;
+    }
+
+    cpi->current_gf_interval = cpi->frames_till_gf_update_due;
+  }
+}
+
+
+void vp9_update_rate_correction_factors(VP9_COMP *cpi, int damp_var) {
+  int    Q = cpi->common.base_qindex;
+  int    correction_factor = 100;
+  double rate_correction_factor;
+  double adjustment_limit;
+
+  int    projected_size_based_on_q = 0;
+
+  // Clear down mmx registers to allow floating point in what follows
+  vp9_clear_system_state();  // __asm emms;
+
+  if (cpi->common.frame_type == KEY_FRAME) {
+    rate_correction_factor = cpi->key_frame_rate_correction_factor;
+  } else {
+    if (cpi->common.refresh_alt_ref_frame || cpi->common.refresh_golden_frame)
+      rate_correction_factor = cpi->gf_rate_correction_factor;
+    else
+      rate_correction_factor = cpi->rate_correction_factor;
+  }
+
+  // Work out how big we would have expected the frame to be at this Q given the current correction factor.
+  // Stay in double to avoid int overflow when values are large
+  projected_size_based_on_q =
+    (int)(((.5 + rate_correction_factor *
+            vp9_bits_per_mb(cpi->common.frame_type, Q)) *
+           cpi->common.MBs) / (1 << BPER_MB_NORMBITS));
+
+  // Make some allowance for cpi->zbin_over_quant
+  if (cpi->zbin_over_quant > 0) {
+    int Z = cpi->zbin_over_quant;
+    double Factor = 0.99;
+    double factor_adjustment = 0.01 / 256.0; // (double)ZBIN_OQ_MAX;
+
+    while (Z > 0) {
+      Z--;
+      projected_size_based_on_q =
+        (int)(Factor * projected_size_based_on_q);
+      Factor += factor_adjustment;
+
+      if (Factor  >= 0.999)
+        Factor = 0.999;
+    }
+  }
+
+  // Work out a size correction factor.
+  // if ( cpi->this_frame_target > 0 )
+  //  correction_factor = (100 * cpi->projected_frame_size) / cpi->this_frame_target;
+  if (projected_size_based_on_q > 0)
+    correction_factor = (100 * cpi->projected_frame_size) / projected_size_based_on_q;
+
+  // More heavily damped adjustment used if we have been oscillating either side of target
+  switch (damp_var) {
+    case 0:
+      adjustment_limit = 0.75;
+      break;
+    case 1:
+      adjustment_limit = 0.375;
+      break;
+    case 2:
+    default:
+      adjustment_limit = 0.25;
+      break;
+  }
+
+  // if ( (correction_factor > 102) && (Q < cpi->active_worst_quality) )
+  if (correction_factor > 102) {
+    // We are not already at the worst allowable quality
+    correction_factor = (int)(100.5 + ((correction_factor - 100) * adjustment_limit));
+    rate_correction_factor = ((rate_correction_factor * correction_factor) / 100);
+
+    // Keep rate_correction_factor within limits
+    if (rate_correction_factor > MAX_BPB_FACTOR)
+      rate_correction_factor = MAX_BPB_FACTOR;
+  }
+  // else if ( (correction_factor < 99) && (Q > cpi->active_best_quality) )
+  else if (correction_factor < 99) {
+    // We are not already at the best allowable quality
+    correction_factor = (int)(100.5 - ((100 - correction_factor) * adjustment_limit));
+    rate_correction_factor = ((rate_correction_factor * correction_factor) / 100);
+
+    // Keep rate_correction_factor within limits
+    if (rate_correction_factor < MIN_BPB_FACTOR)
+      rate_correction_factor = MIN_BPB_FACTOR;
+  }
+
+  if (cpi->common.frame_type == KEY_FRAME)
+    cpi->key_frame_rate_correction_factor = rate_correction_factor;
+  else {
+    if (cpi->common.refresh_alt_ref_frame || cpi->common.refresh_golden_frame)
+      cpi->gf_rate_correction_factor = rate_correction_factor;
+    else
+      cpi->rate_correction_factor = rate_correction_factor;
+  }
+}
+
+
+int vp9_regulate_q(VP9_COMP *cpi, int target_bits_per_frame) {
+  int Q = cpi->active_worst_quality;
+
+  int i;
+  int last_error = INT_MAX;
+  int target_bits_per_mb;
+  int bits_per_mb_at_this_q;
+  double correction_factor;
+
+  // Reset Zbin OQ value
+  cpi->zbin_over_quant = 0;
+
+  // Select the appropriate correction factor based upon type of frame.
+  if (cpi->common.frame_type == KEY_FRAME)
+    correction_factor = cpi->key_frame_rate_correction_factor;
+  else {
+    if (cpi->common.refresh_alt_ref_frame || cpi->common.refresh_golden_frame)
+      correction_factor = cpi->gf_rate_correction_factor;
+    else
+      correction_factor = cpi->rate_correction_factor;
+  }
+
+  // Calculate required scaling factor based on target frame size and size of frame produced using previous Q
+  if (target_bits_per_frame >= (INT_MAX >> BPER_MB_NORMBITS))
+    target_bits_per_mb = (target_bits_per_frame / cpi->common.MBs) << BPER_MB_NORMBITS;       // Case where we would overflow int
+  else
+    target_bits_per_mb = (target_bits_per_frame << BPER_MB_NORMBITS) / cpi->common.MBs;
+
+  i = cpi->active_best_quality;
+
+  do {
+    bits_per_mb_at_this_q =
+      (int)(.5 + correction_factor *
+            vp9_bits_per_mb(cpi->common.frame_type, i));
+
+    if (bits_per_mb_at_this_q <= target_bits_per_mb) {
+      if ((target_bits_per_mb - bits_per_mb_at_this_q) <= last_error)
+        Q = i;
+      else
+        Q = i - 1;
+
+      break;
+    } else
+      last_error = bits_per_mb_at_this_q - target_bits_per_mb;
+  } while (++i <= cpi->active_worst_quality);
+
+
+  // If we are at MAXQ then enable Q over-run which seeks to claw back additional bits through things like
+  // the RD multiplier and zero bin size.
+  if (Q >= MAXQ) {
+    int zbin_oqmax;
+
+    double Factor = 0.99;
+    double factor_adjustment = 0.01 / 256.0; // (double)ZBIN_OQ_MAX;
+
+    if (cpi->common.frame_type == KEY_FRAME)
+      zbin_oqmax = 0; // ZBIN_OQ_MAX/16
+    else if (cpi->common.refresh_alt_ref_frame || (cpi->common.refresh_golden_frame && !cpi->source_alt_ref_active))
+      zbin_oqmax = 16;
+    else
+      zbin_oqmax = ZBIN_OQ_MAX;
+
+    // Each incrment in the zbin is assumed to have a fixed effect on bitrate. This is not of course true.
+    // The effect will be highly clip dependent and may well have sudden steps.
+    // The idea here is to acheive higher effective quantizers than the normal maximum by expanding the zero
+    // bin and hence decreasing the number of low magnitude non zero coefficients.
+    while (cpi->zbin_over_quant < zbin_oqmax) {
+      cpi->zbin_over_quant++;
+
+      if (cpi->zbin_over_quant > zbin_oqmax)
+        cpi->zbin_over_quant = zbin_oqmax;
+
+      // Adjust bits_per_mb_at_this_q estimate
+      bits_per_mb_at_this_q = (int)(Factor * bits_per_mb_at_this_q);
+      Factor += factor_adjustment;
+
+      if (Factor  >= 0.999)
+        Factor = 0.999;
+
+      if (bits_per_mb_at_this_q <= target_bits_per_mb)    // Break out if we get down to the target rate
+        break;
+    }
+
+  }
+
+  return Q;
+}
+
+
+static int estimate_keyframe_frequency(VP9_COMP *cpi) {
+  int i;
+
+  // Average key frame frequency
+  int av_key_frame_frequency = 0;
+
+  /* First key frame at start of sequence is a special case. We have no
+   * frequency data.
+   */
+  if (cpi->key_frame_count == 1) {
+    /* Assume a default of 1 kf every 2 seconds, or the max kf interval,
+     * whichever is smaller.
+     */
+    int key_freq = cpi->oxcf.key_freq > 0 ? cpi->oxcf.key_freq : 1;
+    av_key_frame_frequency = (int)cpi->output_frame_rate * 2;
+
+    if (cpi->oxcf.auto_key && av_key_frame_frequency > key_freq)
+      av_key_frame_frequency = cpi->oxcf.key_freq;
+
+    cpi->prior_key_frame_distance[KEY_FRAME_CONTEXT - 1]
+      = av_key_frame_frequency;
+  } else {
+    unsigned int total_weight = 0;
+    int last_kf_interval =
+      (cpi->frames_since_key > 0) ? cpi->frames_since_key : 1;
+
+    /* reset keyframe context and calculate weighted average of last
+     * KEY_FRAME_CONTEXT keyframes
+     */
+    for (i = 0; i < KEY_FRAME_CONTEXT; i++) {
+      if (i < KEY_FRAME_CONTEXT - 1)
+        cpi->prior_key_frame_distance[i]
+          = cpi->prior_key_frame_distance[i + 1];
+      else
+        cpi->prior_key_frame_distance[i] = last_kf_interval;
+
+      av_key_frame_frequency += prior_key_frame_weight[i]
+                                * cpi->prior_key_frame_distance[i];
+      total_weight += prior_key_frame_weight[i];
+    }
+
+    av_key_frame_frequency  /= total_weight;
+
+  }
+  return av_key_frame_frequency;
+}
+
+
+void vp9_adjust_key_frame_context(VP9_COMP *cpi) {
+  // Clear down mmx registers to allow floating point in what follows
+  vp9_clear_system_state();
+
+  cpi->frames_since_key = 0;
+  cpi->key_frame_count++;
+}
+
+
+void vp9_compute_frame_size_bounds(VP9_COMP *cpi, int *frame_under_shoot_limit,
+                                   int *frame_over_shoot_limit) {
+  // Set-up bounds on acceptable frame size:
+  if (cpi->oxcf.fixed_q >= 0) {
+    // Fixed Q scenario: frame size never outranges target (there is no target!)
+    *frame_under_shoot_limit = 0;
+    *frame_over_shoot_limit  = INT_MAX;
+  } else {
+    if (cpi->common.frame_type == KEY_FRAME) {
+      *frame_over_shoot_limit  = cpi->this_frame_target * 9 / 8;
+      *frame_under_shoot_limit = cpi->this_frame_target * 7 / 8;
+    } else {
+      if (cpi->common.refresh_alt_ref_frame || cpi->common.refresh_golden_frame) {
+        *frame_over_shoot_limit  = cpi->this_frame_target * 9 / 8;
+        *frame_under_shoot_limit = cpi->this_frame_target * 7 / 8;
+      } else {
+        // Stron overshoot limit for constrained quality
+        if (cpi->oxcf.end_usage == USAGE_CONSTRAINED_QUALITY) {
+          *frame_over_shoot_limit  = cpi->this_frame_target * 11 / 8;
+          *frame_under_shoot_limit = cpi->this_frame_target * 2 / 8;
+        } else {
+          *frame_over_shoot_limit  = cpi->this_frame_target * 11 / 8;
+          *frame_under_shoot_limit = cpi->this_frame_target * 5 / 8;
+        }
+      }
+    }
+
+    // For very small rate targets where the fractional adjustment
+    // (eg * 7/8) may be tiny make sure there is at least a minimum
+    // range.
+    *frame_over_shoot_limit += 200;
+    *frame_under_shoot_limit -= 200;
+    if (*frame_under_shoot_limit < 0)
+      *frame_under_shoot_limit = 0;
+  }
+}
+
+
+// return of 0 means drop frame
+int vp9_pick_frame_size(VP9_COMP *cpi) {
+  VP9_COMMON *cm = &cpi->common;
+
+  if (cm->frame_type == KEY_FRAME)
+    calc_iframe_target_size(cpi);
+  else
+    calc_pframe_target_size(cpi);
+
+  return 1;
+}