libvpx: Add VP9 decoder.

source/libvpx/vp9/encoder/vp9_firstpass.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 "math.h"
+#include "limits.h"
+#include "vp9/encoder/vp9_block.h"
+#include "vp9/encoder/vp9_onyx_int.h"
+#include "vp9/encoder/vp9_variance.h"
+#include "vp9/encoder/vp9_encodeintra.h"
+#include "vp9/common/vp9_setupintrarecon.h"
+#include "vp9/encoder/vp9_mcomp.h"
+#include "vp9/encoder/vp9_firstpass.h"
+#include "vpx_scale/vpxscale.h"
+#include "vp9/encoder/vp9_encodeframe.h"
+#include "vp9/encoder/vp9_encodemb.h"
+#include "vp9/common/vp9_extend.h"
+#include "vp9/common/vp9_systemdependent.h"
+#include "vpx_mem/vpx_mem.h"
+#include "vp9/common/vp9_swapyv12buffer.h"
+#include <stdio.h>
+#include "vp9/encoder/vp9_quantize.h"
+#include "vp9/encoder/vp9_rdopt.h"
+#include "vp9/encoder/vp9_ratectrl.h"
+#include "vp9/common/vp9_quant_common.h"
+#include "vp9/common/vp9_entropymv.h"
+#include "vp9/encoder/vp9_encodemv.h"
+#include "./vpx_scale_rtcd.h"
+
+#define OUTPUT_FPF 0
+
+#define IIFACTOR   12.5
+#define IIKFACTOR1 12.5
+#define IIKFACTOR2 15.0
+#define RMAX       128.0
+#define GF_RMAX    96.0
+#define ERR_DIVISOR   150.0
+
+#define KF_MB_INTRA_MIN 300
+#define GF_MB_INTRA_MIN 200
+
+#define DOUBLE_DIVIDE_CHECK(X) ((X)<0?(X)-.000001:(X)+.000001)
+
+#define POW1 (double)cpi->oxcf.two_pass_vbrbias/100.0
+#define POW2 (double)cpi->oxcf.two_pass_vbrbias/100.0
+
+static void find_next_key_frame(VP9_COMP *cpi, FIRSTPASS_STATS *this_frame);
+
+static int select_cq_level(int qindex) {
+  int ret_val = QINDEX_RANGE - 1;
+  int i;
+
+  double target_q = (vp9_convert_qindex_to_q(qindex) * 0.5847) + 1.0;
+
+  for (i = 0; i < QINDEX_RANGE; i++) {
+    if (target_q <= vp9_convert_qindex_to_q(i)) {
+      ret_val = i;
+      break;
+    }
+  }
+
+  return ret_val;
+}
+
+
+// Resets the first pass file to the given position using a relative seek from the current position
+static void reset_fpf_position(VP9_COMP *cpi, FIRSTPASS_STATS *Position) {
+  cpi->twopass.stats_in = Position;
+}
+
+static int lookup_next_frame_stats(VP9_COMP *cpi, FIRSTPASS_STATS *next_frame) {
+  if (cpi->twopass.stats_in >= cpi->twopass.stats_in_end)
+    return EOF;
+
+  *next_frame = *cpi->twopass.stats_in;
+  return 1;
+}
+
+// Read frame stats at an offset from the current position
+static int read_frame_stats(VP9_COMP *cpi,
+                            FIRSTPASS_STATS *frame_stats,
+                            int offset) {
+  FIRSTPASS_STATS *fps_ptr = cpi->twopass.stats_in;
+
+  // Check legality of offset
+  if (offset >= 0) {
+    if (&fps_ptr[offset] >= cpi->twopass.stats_in_end)
+      return EOF;
+  } else if (offset < 0) {
+    if (&fps_ptr[offset] < cpi->twopass.stats_in_start)
+      return EOF;
+  }
+
+  *frame_stats = fps_ptr[offset];
+  return 1;
+}
+
+static int input_stats(VP9_COMP *cpi, FIRSTPASS_STATS *fps) {
+  if (cpi->twopass.stats_in >= cpi->twopass.stats_in_end)
+    return EOF;
+
+  *fps = *cpi->twopass.stats_in;
+  cpi->twopass.stats_in =
+    (void *)((char *)cpi->twopass.stats_in + sizeof(FIRSTPASS_STATS));
+  return 1;
+}
+
+static void output_stats(const VP9_COMP            *cpi,
+                         struct vpx_codec_pkt_list *pktlist,
+                         FIRSTPASS_STATS            *stats) {
+  struct vpx_codec_cx_pkt pkt;
+  pkt.kind = VPX_CODEC_STATS_PKT;
+  pkt.data.twopass_stats.buf = stats;
+  pkt.data.twopass_stats.sz = sizeof(FIRSTPASS_STATS);
+  vpx_codec_pkt_list_add(pktlist, &pkt);
+
+// TEMP debug code
+#if OUTPUT_FPF
+
+  {
+    FILE *fpfile;
+    fpfile = fopen("firstpass.stt", "a");
+
+    fprintf(fpfile, "%12.0f %12.0f %12.0f %12.0f %12.0f %12.4f %12.4f"
+            "%12.4f %12.4f %12.4f %12.4f %12.4f %12.4f %12.4f"
+            "%12.0f %12.0f %12.4f %12.0f %12.0f %12.4f\n",
+            stats->frame,
+            stats->intra_error,
+            stats->coded_error,
+            stats->sr_coded_error,
+            stats->ssim_weighted_pred_err,
+            stats->pcnt_inter,
+            stats->pcnt_motion,
+            stats->pcnt_second_ref,
+            stats->pcnt_neutral,
+            stats->MVr,
+            stats->mvr_abs,
+            stats->MVc,
+            stats->mvc_abs,
+            stats->MVrv,
+            stats->MVcv,
+            stats->mv_in_out_count,
+            stats->new_mv_count,
+            stats->count,
+            stats->duration);
+    fclose(fpfile);
+  }
+#endif
+}
+
+static void zero_stats(FIRSTPASS_STATS *section) {
+  section->frame      = 0.0;
+  section->intra_error = 0.0;
+  section->coded_error = 0.0;
+  section->sr_coded_error = 0.0;
+  section->ssim_weighted_pred_err = 0.0;
+  section->pcnt_inter  = 0.0;
+  section->pcnt_motion  = 0.0;
+  section->pcnt_second_ref = 0.0;
+  section->pcnt_neutral = 0.0;
+  section->MVr        = 0.0;
+  section->mvr_abs     = 0.0;
+  section->MVc        = 0.0;
+  section->mvc_abs     = 0.0;
+  section->MVrv       = 0.0;
+  section->MVcv       = 0.0;
+  section->mv_in_out_count  = 0.0;
+  section->new_mv_count = 0.0;
+  section->count      = 0.0;
+  section->duration   = 1.0;
+}
+
+static void accumulate_stats(FIRSTPASS_STATS *section, FIRSTPASS_STATS *frame) {
+  section->frame += frame->frame;
+  section->intra_error += frame->intra_error;
+  section->coded_error += frame->coded_error;
+  section->sr_coded_error += frame->sr_coded_error;
+  section->ssim_weighted_pred_err += frame->ssim_weighted_pred_err;
+  section->pcnt_inter  += frame->pcnt_inter;
+  section->pcnt_motion += frame->pcnt_motion;
+  section->pcnt_second_ref += frame->pcnt_second_ref;
+  section->pcnt_neutral += frame->pcnt_neutral;
+  section->MVr        += frame->MVr;
+  section->mvr_abs     += frame->mvr_abs;
+  section->MVc        += frame->MVc;
+  section->mvc_abs     += frame->mvc_abs;
+  section->MVrv       += frame->MVrv;
+  section->MVcv       += frame->MVcv;
+  section->mv_in_out_count  += frame->mv_in_out_count;
+  section->new_mv_count += frame->new_mv_count;
+  section->count      += frame->count;
+  section->duration   += frame->duration;
+}
+
+static void subtract_stats(FIRSTPASS_STATS *section, FIRSTPASS_STATS *frame) {
+  section->frame -= frame->frame;
+  section->intra_error -= frame->intra_error;
+  section->coded_error -= frame->coded_error;
+  section->sr_coded_error -= frame->sr_coded_error;
+  section->ssim_weighted_pred_err -= frame->ssim_weighted_pred_err;
+  section->pcnt_inter  -= frame->pcnt_inter;
+  section->pcnt_motion -= frame->pcnt_motion;
+  section->pcnt_second_ref -= frame->pcnt_second_ref;
+  section->pcnt_neutral -= frame->pcnt_neutral;
+  section->MVr        -= frame->MVr;
+  section->mvr_abs     -= frame->mvr_abs;
+  section->MVc        -= frame->MVc;
+  section->mvc_abs     -= frame->mvc_abs;
+  section->MVrv       -= frame->MVrv;
+  section->MVcv       -= frame->MVcv;
+  section->mv_in_out_count  -= frame->mv_in_out_count;
+  section->new_mv_count -= frame->new_mv_count;
+  section->count      -= frame->count;
+  section->duration   -= frame->duration;
+}
+
+static void avg_stats(FIRSTPASS_STATS *section) {
+  if (section->count < 1.0)
+    return;
+
+  section->intra_error /= section->count;
+  section->coded_error /= section->count;
+  section->sr_coded_error /= section->count;
+  section->ssim_weighted_pred_err /= section->count;
+  section->pcnt_inter  /= section->count;
+  section->pcnt_second_ref /= section->count;
+  section->pcnt_neutral /= section->count;
+  section->pcnt_motion /= section->count;
+  section->MVr        /= section->count;
+  section->mvr_abs     /= section->count;
+  section->MVc        /= section->count;
+  section->mvc_abs     /= section->count;
+  section->MVrv       /= section->count;
+  section->MVcv       /= section->count;
+  section->mv_in_out_count   /= section->count;
+  section->duration   /= section->count;
+}
+
+// Calculate a modified Error used in distributing bits between easier and harder frames
+static double calculate_modified_err(VP9_COMP *cpi, FIRSTPASS_STATS *this_frame) {
+  double av_err = (cpi->twopass.total_stats->ssim_weighted_pred_err /
+                   cpi->twopass.total_stats->count);
+  double this_err = this_frame->ssim_weighted_pred_err;
+  double modified_err;
+
+  if (this_err > av_err)
+    modified_err = av_err * pow((this_err / DOUBLE_DIVIDE_CHECK(av_err)), POW1);
+  else
+    modified_err = av_err * pow((this_err / DOUBLE_DIVIDE_CHECK(av_err)), POW2);
+
+  return modified_err;
+}
+
+static const double weight_table[256] = {
+  0.020000, 0.020000, 0.020000, 0.020000, 0.020000, 0.020000, 0.020000, 0.020000,
+  0.020000, 0.020000, 0.020000, 0.020000, 0.020000, 0.020000, 0.020000, 0.020000,
+  0.020000, 0.020000, 0.020000, 0.020000, 0.020000, 0.020000, 0.020000, 0.020000,
+  0.020000, 0.020000, 0.020000, 0.020000, 0.020000, 0.020000, 0.020000, 0.020000,
+  0.020000, 0.031250, 0.062500, 0.093750, 0.125000, 0.156250, 0.187500, 0.218750,
+  0.250000, 0.281250, 0.312500, 0.343750, 0.375000, 0.406250, 0.437500, 0.468750,
+  0.500000, 0.531250, 0.562500, 0.593750, 0.625000, 0.656250, 0.687500, 0.718750,
+  0.750000, 0.781250, 0.812500, 0.843750, 0.875000, 0.906250, 0.937500, 0.968750,
+  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000,
+  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000,
+  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000,
+  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000,
+  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000,
+  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000,
+  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000,
+  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000,
+  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000,
+  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000,
+  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000,
+  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000,
+  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000,
+  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000,
+  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000,
+  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000,
+  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000,
+  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000,
+  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000,
+  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000,
+  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000,
+  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000,
+  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000,
+  1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000
+};
+
+static double simple_weight(YV12_BUFFER_CONFIG *source) {
+  int i, j;
+
+  unsigned char *src = source->y_buffer;
+  double sum_weights = 0.0;
+
+  // Loop throught the Y plane raw examining levels and creating a weight for the image
+  i = source->y_height;
+  do {
+    j = source->y_width;
+    do {
+      sum_weights += weight_table[ *src];
+      src++;
+    } while (--j);
+    src -= source->y_width;
+    src += source->y_stride;
+  } while (--i);
+
+  sum_weights /= (source->y_height * source->y_width);
+
+  return sum_weights;
+}
+
+
+// This function returns the current per frame maximum bitrate target
+static int frame_max_bits(VP9_COMP *cpi) {
+  // Max allocation for a single frame based on the max section guidelines passed in and how many bits are left
+  int max_bits;
+
+  // For VBR base this on the bits and frames left plus the two_pass_vbrmax_section rate passed in by the user
+  max_bits = (int)(((double)cpi->twopass.bits_left / (cpi->twopass.total_stats->count - (double)cpi->common.current_video_frame)) * ((double)cpi->oxcf.two_pass_vbrmax_section / 100.0));
+
+  // Trap case where we are out of bits
+  if (max_bits < 0)
+    max_bits = 0;
+
+  return max_bits;
+}
+
+void vp9_init_first_pass(VP9_COMP *cpi) {
+  zero_stats(cpi->twopass.total_stats);
+}
+
+void vp9_end_first_pass(VP9_COMP *cpi) {
+  output_stats(cpi, cpi->output_pkt_list, cpi->twopass.total_stats);
+}
+
+static void zz_motion_search(VP9_COMP *cpi, MACROBLOCK *x, YV12_BUFFER_CONFIG *recon_buffer, int *best_motion_err, int recon_yoffset) {
+  MACROBLOCKD *const xd = &x->e_mbd;
+  BLOCK *b = &x->block[0];
+  BLOCKD *d = &x->e_mbd.block[0];
+
+  unsigned char *src_ptr = (*(b->base_src) + b->src);
+  int src_stride = b->src_stride;
+  unsigned char *ref_ptr;
+  int ref_stride = d->pre_stride;
+
+  // Set up pointers for this macro block recon buffer
+  xd->pre.y_buffer = recon_buffer->y_buffer + recon_yoffset;
+
+  ref_ptr = (unsigned char *)(*(d->base_pre) + d->pre);
+
+  vp9_mse16x16(src_ptr, src_stride, ref_ptr, ref_stride,
+               (unsigned int *)(best_motion_err));
+}
+
+static void first_pass_motion_search(VP9_COMP *cpi, MACROBLOCK *x,
+                                     int_mv *ref_mv, MV *best_mv,
+                                     YV12_BUFFER_CONFIG *recon_buffer,
+                                     int *best_motion_err, int recon_yoffset) {
+  MACROBLOCKD *const xd = &x->e_mbd;
+  BLOCK *b = &x->block[0];
+  BLOCKD *d = &x->e_mbd.block[0];
+  int num00;
+
+  int_mv tmp_mv;
+  int_mv ref_mv_full;
+
+  int tmp_err;
+  int step_param = 3;
+  int further_steps = (MAX_MVSEARCH_STEPS - 1) - step_param;
+  int n;
+  vp9_variance_fn_ptr_t v_fn_ptr = cpi->fn_ptr[BLOCK_16X16];
+  int new_mv_mode_penalty = 256;
+
+  // override the default variance function to use MSE
+  v_fn_ptr.vf = vp9_mse16x16;
+
+  // Set up pointers for this macro block recon buffer
+  xd->pre.y_buffer = recon_buffer->y_buffer + recon_yoffset;
+
+  // Initial step/diamond search centred on best mv
+  tmp_mv.as_int = 0;
+  ref_mv_full.as_mv.col = ref_mv->as_mv.col >> 3;
+  ref_mv_full.as_mv.row = ref_mv->as_mv.row >> 3;
+  tmp_err = cpi->diamond_search_sad(x, b, d, &ref_mv_full, &tmp_mv, step_param,
+                                    x->sadperbit16, &num00, &v_fn_ptr,
+                                    x->nmvjointcost,
+                                    x->mvcost, ref_mv);
+  if (tmp_err < INT_MAX - new_mv_mode_penalty)
+    tmp_err += new_mv_mode_penalty;
+
+  if (tmp_err < *best_motion_err) {
+    *best_motion_err = tmp_err;
+    best_mv->row = tmp_mv.as_mv.row;
+    best_mv->col = tmp_mv.as_mv.col;
+  }
+
+  // Further step/diamond searches as necessary
+  n = num00;
+  num00 = 0;
+
+  while (n < further_steps) {
+    n++;
+
+    if (num00)
+      num00--;
+    else {
+      tmp_err = cpi->diamond_search_sad(x, b, d, &ref_mv_full, &tmp_mv,
+                                        step_param + n, x->sadperbit16,
+                                        &num00, &v_fn_ptr,
+                                        x->nmvjointcost,
+                                        x->mvcost, ref_mv);
+      if (tmp_err < INT_MAX - new_mv_mode_penalty)
+        tmp_err += new_mv_mode_penalty;
+
+      if (tmp_err < *best_motion_err) {
+        *best_motion_err = tmp_err;
+        best_mv->row = tmp_mv.as_mv.row;
+        best_mv->col = tmp_mv.as_mv.col;
+      }
+    }
+  }
+}
+
+void vp9_first_pass(VP9_COMP *cpi) {
+  int mb_row, mb_col;
+  MACROBLOCK *const x = &cpi->mb;
+  VP9_COMMON *const cm = &cpi->common;
+  MACROBLOCKD *const xd = &x->e_mbd;
+
+  int recon_yoffset, recon_uvoffset;
+  YV12_BUFFER_CONFIG *lst_yv12 = &cm->yv12_fb[cm->lst_fb_idx];
+  YV12_BUFFER_CONFIG *new_yv12 = &cm->yv12_fb[cm->new_fb_idx];
+  YV12_BUFFER_CONFIG *gld_yv12 = &cm->yv12_fb[cm->gld_fb_idx];
+  int recon_y_stride = lst_yv12->y_stride;
+  int recon_uv_stride = lst_yv12->uv_stride;
+  int64_t intra_error = 0;
+  int64_t coded_error = 0;
+  int64_t sr_coded_error = 0;
+
+  int sum_mvr = 0, sum_mvc = 0;
+  int sum_mvr_abs = 0, sum_mvc_abs = 0;
+  int sum_mvrs = 0, sum_mvcs = 0;
+  int mvcount = 0;
+  int intercount = 0;
+  int second_ref_count = 0;
+  int intrapenalty = 256;
+  int neutral_count = 0;
+  int new_mv_count = 0;
+  int sum_in_vectors = 0;
+  uint32_t lastmv_as_int = 0;
+
+  int_mv zero_ref_mv;
+
+  zero_ref_mv.as_int = 0;
+
+  vp9_clear_system_state();  // __asm emms;
+
+  x->src = * cpi->Source;
+  xd->pre = *lst_yv12;
+  xd->dst = *new_yv12;
+
+  x->partition_info = x->pi;
+
+  xd->mode_info_context = cm->mi;
+
+  vp9_build_block_offsets(x);
+
+  vp9_setup_block_dptrs(&x->e_mbd);
+
+  vp9_setup_block_ptrs(x);
+
+  // set up frame new frame for intra coded blocks
+  vp9_setup_intra_recon(new_yv12);
+  vp9_frame_init_quantizer(cpi);
+
+  // Initialise the MV cost table to the defaults
+  // if( cm->current_video_frame == 0)
+  // if ( 0 )
+  {
+    vp9_init_mv_probs(cm);
+    vp9_initialize_rd_consts(cpi, cm->base_qindex + cm->y1dc_delta_q);
+  }
+
+  // for each macroblock row in image
+  for (mb_row = 0; mb_row < cm->mb_rows; mb_row++) {
+    int_mv best_ref_mv;
+
+    best_ref_mv.as_int = 0;
+
+    // reset above block coeffs
+    xd->up_available = (mb_row != 0);
+    recon_yoffset = (mb_row * recon_y_stride * 16);
+    recon_uvoffset = (mb_row * recon_uv_stride * 8);
+
+    // Set up limit values for motion vectors to prevent them extending outside the UMV borders
+    x->mv_row_min = -((mb_row * 16) + (VP9BORDERINPIXELS - 16));
+    x->mv_row_max = ((cm->mb_rows - 1 - mb_row) * 16)
+                    + (VP9BORDERINPIXELS - 16);
+
+
+    // for each macroblock col in image
+    for (mb_col = 0; mb_col < cm->mb_cols; mb_col++) {
+      int this_error;
+      int gf_motion_error = INT_MAX;
+      int use_dc_pred = (mb_col || mb_row) && (!mb_col || !mb_row);
+
+      xd->dst.y_buffer = new_yv12->y_buffer + recon_yoffset;
+      xd->dst.u_buffer = new_yv12->u_buffer + recon_uvoffset;
+      xd->dst.v_buffer = new_yv12->v_buffer + recon_uvoffset;
+      xd->left_available = (mb_col != 0);
+
+#if !CONFIG_SUPERBLOCKS
+      // Copy current mb to a buffer
+      vp9_copy_mem16x16(x->src.y_buffer, x->src.y_stride, x->thismb, 16);
+#endif
+
+      // do intra 16x16 prediction
+      this_error = vp9_encode_intra(cpi, x, use_dc_pred);
+
+      // "intrapenalty" below deals with situations where the intra and inter error scores are very low (eg a plain black frame)
+      // We do not have special cases in first pass for 0,0 and nearest etc so all inter modes carry an overhead cost estimate fot the mv.
+      // When the error score is very low this causes us to pick all or lots of INTRA modes and throw lots of key frames.
+      // This penalty adds a cost matching that of a 0,0 mv to the intra case.
+      this_error += intrapenalty;
+
+      // Cumulative intra error total
+      intra_error += (int64_t)this_error;
+
+      // Set up limit values for motion vectors to prevent them extending outside the UMV borders
+      x->mv_col_min = -((mb_col * 16) + (VP9BORDERINPIXELS - 16));
+      x->mv_col_max = ((cm->mb_cols - 1 - mb_col) * 16)
+                      + (VP9BORDERINPIXELS - 16);
+
+      // Other than for the first frame do a motion search
+      if (cm->current_video_frame > 0) {
+        int tmp_err;
+        int motion_error = INT_MAX;
+        int_mv mv, tmp_mv;
+
+        // Simple 0,0 motion with no mv overhead
+        zz_motion_search(cpi, x, lst_yv12, &motion_error, recon_yoffset);
+        mv.as_int = tmp_mv.as_int = 0;
+
+        // Test last reference frame using the previous best mv as the
+        // starting point (best reference) for the search
+        first_pass_motion_search(cpi, x, &best_ref_mv,
+                                 &mv.as_mv, lst_yv12,
+                                 &motion_error, recon_yoffset);
+
+        // If the current best reference mv is not centred on 0,0 then do a 0,0 based search as well
+        if (best_ref_mv.as_int) {
+          tmp_err = INT_MAX;
+          first_pass_motion_search(cpi, x, &zero_ref_mv, &tmp_mv.as_mv,
+                                   lst_yv12, &tmp_err, recon_yoffset);
+
+          if (tmp_err < motion_error) {
+            motion_error = tmp_err;
+            mv.as_int = tmp_mv.as_int;
+          }
+        }
+
+        // Experimental search in an older reference frame
+        if (cm->current_video_frame > 1) {
+          // Simple 0,0 motion with no mv overhead
+          zz_motion_search(cpi, x, gld_yv12,
+                           &gf_motion_error, recon_yoffset);
+
+          first_pass_motion_search(cpi, x, &zero_ref_mv,
+                                   &tmp_mv.as_mv, gld_yv12,
+                                   &gf_motion_error, recon_yoffset);
+
+          if ((gf_motion_error < motion_error) &&
+              (gf_motion_error < this_error)) {
+            second_ref_count++;
+          }
+
+          // Reset to last frame as reference buffer
+          xd->pre.y_buffer = lst_yv12->y_buffer + recon_yoffset;
+          xd->pre.u_buffer = lst_yv12->u_buffer + recon_uvoffset;
+          xd->pre.v_buffer = lst_yv12->v_buffer + recon_uvoffset;
+
+          // In accumulating a score for the older reference frame
+          // take the best of the motion predicted score and
+          // the intra coded error (just as will be done for)
+          // accumulation of "coded_error" for the last frame.
+          if (gf_motion_error < this_error)
+            sr_coded_error += gf_motion_error;
+          else
+            sr_coded_error += this_error;
+        } else
+          sr_coded_error += motion_error;
+
+        /* Intra assumed best */
+        best_ref_mv.as_int = 0;
+
+        if (motion_error <= this_error) {
+          // Keep a count of cases where the inter and intra were
+          // very close and very low. This helps with scene cut
+          // detection for example in cropped clips with black bars
+          // at the sides or top and bottom.
+          if ((((this_error - intrapenalty) * 9) <=
+               (motion_error * 10)) &&
+              (this_error < (2 * intrapenalty))) {
+            neutral_count++;
+          }
+
+          mv.as_mv.row <<= 3;
+          mv.as_mv.col <<= 3;
+          this_error = motion_error;
+          vp9_set_mbmode_and_mvs(x, NEWMV, &mv);
+          xd->mode_info_context->mbmi.txfm_size = TX_4X4;
+          vp9_encode_inter16x16y(x);
+          sum_mvr += mv.as_mv.row;
+          sum_mvr_abs += abs(mv.as_mv.row);
+          sum_mvc += mv.as_mv.col;
+          sum_mvc_abs += abs(mv.as_mv.col);
+          sum_mvrs += mv.as_mv.row * mv.as_mv.row;
+          sum_mvcs += mv.as_mv.col * mv.as_mv.col;
+          intercount++;
+
+          best_ref_mv.as_int = mv.as_int;
+
+          // Was the vector non-zero
+          if (mv.as_int) {
+            mvcount++;
+
+            // Was it different from the last non zero vector
+            if (mv.as_int != lastmv_as_int)
+              new_mv_count++;
+            lastmv_as_int = mv.as_int;
+
+            // Does the Row vector point inwards or outwards
+            if (mb_row < cm->mb_rows / 2) {
+              if (mv.as_mv.row > 0)
+                sum_in_vectors--;
+              else if (mv.as_mv.row < 0)
+                sum_in_vectors++;
+            } else if (mb_row > cm->mb_rows / 2) {
+              if (mv.as_mv.row > 0)
+                sum_in_vectors++;
+              else if (mv.as_mv.row < 0)
+                sum_in_vectors--;
+            }
+
+            // Does the Row vector point inwards or outwards
+            if (mb_col < cm->mb_cols / 2) {
+              if (mv.as_mv.col > 0)
+                sum_in_vectors--;
+              else if (mv.as_mv.col < 0)
+                sum_in_vectors++;
+            } else if (mb_col > cm->mb_cols / 2) {
+              if (mv.as_mv.col > 0)
+                sum_in_vectors++;
+              else if (mv.as_mv.col < 0)
+                sum_in_vectors--;
+            }
+          }
+        }
+      } else
+        sr_coded_error += (int64_t)this_error;
+
+      coded_error += (int64_t)this_error;
+
+      // adjust to the next column of macroblocks
+      x->src.y_buffer += 16;
+      x->src.u_buffer += 8;
+      x->src.v_buffer += 8;
+
+      recon_yoffset += 16;
+      recon_uvoffset += 8;
+    }
+
+    // adjust to the next row of mbs
+    x->src.y_buffer += 16 * x->src.y_stride - 16 * cm->mb_cols;
+    x->src.u_buffer += 8 * x->src.uv_stride - 8 * cm->mb_cols;
+    x->src.v_buffer += 8 * x->src.uv_stride - 8 * cm->mb_cols;
+
+    // extend the recon for intra prediction
+    vp9_extend_mb_row(new_yv12, xd->dst.y_buffer + 16,
+                      xd->dst.u_buffer + 8, xd->dst.v_buffer + 8);
+    vp9_clear_system_state();  // __asm emms;
+  }
+
+  vp9_clear_system_state();  // __asm emms;
+  {
+    double weight = 0.0;
+
+    FIRSTPASS_STATS fps;
+
+    fps.frame      = cm->current_video_frame;
+    fps.intra_error = (double)(intra_error >> 8);
+    fps.coded_error = (double)(coded_error >> 8);
+    fps.sr_coded_error = (double)(sr_coded_error >> 8);
+    weight = simple_weight(cpi->Source);
+
+
+    if (weight < 0.1)
+      weight = 0.1;
+
+    fps.ssim_weighted_pred_err = fps.coded_error * weight;
+
+    fps.pcnt_inter  = 0.0;
+    fps.pcnt_motion = 0.0;
+    fps.MVr        = 0.0;
+    fps.mvr_abs     = 0.0;
+    fps.MVc        = 0.0;
+    fps.mvc_abs     = 0.0;
+    fps.MVrv       = 0.0;
+    fps.MVcv       = 0.0;
+    fps.mv_in_out_count  = 0.0;
+    fps.new_mv_count = 0.0;
+    fps.count      = 1.0;
+
+    fps.pcnt_inter   = 1.0 * (double)intercount / cm->MBs;
+    fps.pcnt_second_ref = 1.0 * (double)second_ref_count / cm->MBs;
+    fps.pcnt_neutral = 1.0 * (double)neutral_count / cm->MBs;
+
+    if (mvcount > 0) {
+      fps.MVr = (double)sum_mvr / (double)mvcount;
+      fps.mvr_abs = (double)sum_mvr_abs / (double)mvcount;
+      fps.MVc = (double)sum_mvc / (double)mvcount;
+      fps.mvc_abs = (double)sum_mvc_abs / (double)mvcount;
+      fps.MVrv = ((double)sum_mvrs - (fps.MVr * fps.MVr / (double)mvcount)) / (double)mvcount;
+      fps.MVcv = ((double)sum_mvcs - (fps.MVc * fps.MVc / (double)mvcount)) / (double)mvcount;
+      fps.mv_in_out_count = (double)sum_in_vectors / (double)(mvcount * 2);
+      fps.new_mv_count = new_mv_count;
+
+      fps.pcnt_motion = 1.0 * (double)mvcount / cpi->common.MBs;
+    }
+
+    // TODO:  handle the case when duration is set to 0, or something less
+    // than the full time between subsequent cpi->source_time_stamp s  .
+    fps.duration = (double)(cpi->source->ts_end
+                            - cpi->source->ts_start);
+
+    // don't want to do output stats with a stack variable!
+    memcpy(cpi->twopass.this_frame_stats,
+           &fps,
+           sizeof(FIRSTPASS_STATS));
+    output_stats(cpi, cpi->output_pkt_list, cpi->twopass.this_frame_stats);
+    accumulate_stats(cpi->twopass.total_stats, &fps);
+  }
+
+  // Copy the previous Last Frame back into gf and and arf buffers if
+  // the prediction is good enough... but also dont allow it to lag too far
+  if ((cpi->twopass.sr_update_lag > 3) ||
+      ((cm->current_video_frame > 0) &&
+       (cpi->twopass.this_frame_stats->pcnt_inter > 0.20) &&
+       ((cpi->twopass.this_frame_stats->intra_error /
+         cpi->twopass.this_frame_stats->coded_error) > 2.0))) {
+    vp8_yv12_copy_frame(lst_yv12, gld_yv12);
+    cpi->twopass.sr_update_lag = 1;
+  } else
+    cpi->twopass.sr_update_lag++;
+
+  // swap frame pointers so last frame refers to the frame we just compressed
+  vp9_swap_yv12_buffer(lst_yv12, new_yv12);
+  vp8_yv12_extend_frame_borders(lst_yv12);
+
+  // Special case for the first frame. Copy into the GF buffer as a second reference.
+  if (cm->current_video_frame == 0) {
+    vp8_yv12_copy_frame(lst_yv12, gld_yv12);
+  }
+
+
+  // use this to see what the first pass reconstruction looks like
+  if (0) {
+    char filename[512];
+    FILE *recon_file;
+    sprintf(filename, "enc%04d.yuv", (int) cm->current_video_frame);
+
+    if (cm->current_video_frame == 0)
+      recon_file = fopen(filename, "wb");
+    else
+      recon_file = fopen(filename, "ab");
+
+    (void)fwrite(lst_yv12->buffer_alloc, lst_yv12->frame_size, 1, recon_file);
+    fclose(recon_file);
+  }
+
+  cm->current_video_frame++;
+
+}
+
+// Estimate a cost per mb attributable to overheads such as the coding of
+// modes and motion vectors.
+// Currently simplistic in its assumptions for testing.
+//
+
+
+static double bitcost(double prob) {
+  return -(log(prob) / log(2.0));
+}
+
+static long long estimate_modemvcost(VP9_COMP *cpi,
+                                     FIRSTPASS_STATS *fpstats) {
+  int mv_cost;
+  int mode_cost;
+
+  double av_pct_inter = fpstats->pcnt_inter / fpstats->count;
+  double av_pct_motion = fpstats->pcnt_motion / fpstats->count;
+  double av_intra = (1.0 - av_pct_inter);
+
+  double zz_cost;
+  double motion_cost;
+  double intra_cost;
+
+  zz_cost = bitcost(av_pct_inter - av_pct_motion);
+  motion_cost = bitcost(av_pct_motion);
+  intra_cost = bitcost(av_intra);
+
+  // Estimate of extra bits per mv overhead for mbs
+  // << 9 is the normalization to the (bits * 512) used in vp9_bits_per_mb
+  mv_cost = ((int)(fpstats->new_mv_count / fpstats->count) * 8) << 9;
+
+  // Crude estimate of overhead cost from modes
+  // << 9 is the normalization to (bits * 512) used in vp9_bits_per_mb
+  mode_cost =
+    (int)((((av_pct_inter - av_pct_motion) * zz_cost) +
+           (av_pct_motion * motion_cost) +
+           (av_intra * intra_cost)) * cpi->common.MBs) << 9;
+
+  // return mv_cost + mode_cost;
+  // TODO PGW Fix overhead costs for extended Q range
+  return 0;
+}
+
+static double calc_correction_factor(double err_per_mb,
+                                     double err_divisor,
+                                     double pt_low,
+                                     double pt_high,
+                                     int Q) {
+  double power_term;
+  double error_term = err_per_mb / err_divisor;
+  double correction_factor;
+
+  // Adjustment based on actual quantizer to power term.
+  power_term = (vp9_convert_qindex_to_q(Q) * 0.01) + pt_low;
+  power_term = (power_term > pt_high) ? pt_high : power_term;
+
+  // Adjustments to error term
+  // TBD
+
+  // Calculate correction factor
+  correction_factor = pow(error_term, power_term);
+
+  // Clip range
+  correction_factor =
+    (correction_factor < 0.05)
+    ? 0.05 : (correction_factor > 2.0) ? 2.0 : correction_factor;
+
+  return correction_factor;
+}
+
+// Given a current maxQ value sets a range for future values.
+// PGW TODO..
+// This code removes direct dependency on QIndex to determin the range
+// (now uses the actual quantizer) but has not been tuned.
+static void adjust_maxq_qrange(VP9_COMP *cpi) {
+  int i;
+  double q;
+
+  // Set the max corresponding to cpi->avg_q * 2.0
+  q = cpi->avg_q * 2.0;
+  cpi->twopass.maxq_max_limit = cpi->worst_quality;
+  for (i = cpi->best_quality; i <= cpi->worst_quality; i++) {
+    cpi->twopass.maxq_max_limit = i;
+    if (vp9_convert_qindex_to_q(i) >= q)
+      break;
+  }
+
+  // Set the min corresponding to cpi->avg_q * 0.5
+  q = cpi->avg_q * 0.5;
+  cpi->twopass.maxq_min_limit = cpi->best_quality;
+  for (i = cpi->worst_quality; i >= cpi->best_quality; i--) {
+    cpi->twopass.maxq_min_limit = i;
+    if (vp9_convert_qindex_to_q(i) <= q)
+      break;
+  }
+}
+
+static int estimate_max_q(VP9_COMP *cpi,
+                          FIRSTPASS_STATS *fpstats,
+                          int section_target_bandwitdh,
+                          int overhead_bits) {
+  int Q;
+  int num_mbs = cpi->common.MBs;
+  int target_norm_bits_per_mb;
+
+  double section_err = (fpstats->coded_error / fpstats->count);
+  double sr_err_diff;
+  double sr_correction;
+  double err_per_mb = section_err / num_mbs;
+  double err_correction_factor;
+  double speed_correction = 1.0;
+  double overhead_bits_per_mb;
+
+  if (section_target_bandwitdh <= 0)
+    return cpi->twopass.maxq_max_limit;          // Highest value allowed
+
+  target_norm_bits_per_mb =
+    (section_target_bandwitdh < (1 << 20))
+    ? (512 * section_target_bandwitdh) / num_mbs
+    : 512 * (section_target_bandwitdh / num_mbs);
+
+  // Look at the drop in prediction quality between the last frame
+  // and the GF buffer (which contained an older frame).
+  sr_err_diff =
+    (fpstats->sr_coded_error - fpstats->coded_error) /
+    (fpstats->count * cpi->common.MBs);
+  sr_correction = (sr_err_diff / 32.0);
+  sr_correction = pow(sr_correction, 0.25);
+  if (sr_correction < 0.75)
+    sr_correction = 0.75;
+  else if (sr_correction > 1.25)
+    sr_correction = 1.25;
+
+  // Calculate a corrective factor based on a rolling ratio of bits spent
+  // vs target bits
+  if ((cpi->rolling_target_bits > 0) &&
+      (cpi->active_worst_quality < cpi->worst_quality)) {
+    double rolling_ratio;
+
+    rolling_ratio = (double)cpi->rolling_actual_bits /
+                    (double)cpi->rolling_target_bits;
+
+    if (rolling_ratio < 0.95)
+      cpi->twopass.est_max_qcorrection_factor -= 0.005;
+    else if (rolling_ratio > 1.05)
+      cpi->twopass.est_max_qcorrection_factor += 0.005;
+
+    cpi->twopass.est_max_qcorrection_factor =
+      (cpi->twopass.est_max_qcorrection_factor < 0.1)
+      ? 0.1
+      : (cpi->twopass.est_max_qcorrection_factor > 10.0)
+      ? 10.0 : cpi->twopass.est_max_qcorrection_factor;
+  }
+
+  // Corrections for higher compression speed settings
+  // (reduced compression expected)
+  if (cpi->compressor_speed == 1) {
+    if (cpi->oxcf.cpu_used <= 5)
+      speed_correction = 1.04 + (cpi->oxcf.cpu_used * 0.04);
+    else
+      speed_correction = 1.25;
+  }
+
+  // Estimate of overhead bits per mb
+  // Correction to overhead bits for min allowed Q.
+  // PGW TODO.. This code is broken for the extended Q range
+  //            for now overhead set to 0.
+  overhead_bits_per_mb = overhead_bits / num_mbs;
+  overhead_bits_per_mb *= pow(0.98, (double)cpi->twopass.maxq_min_limit);
+
+  // Try and pick a max Q that will be high enough to encode the
+  // content at the given rate.
+  for (Q = cpi->twopass.maxq_min_limit; Q < cpi->twopass.maxq_max_limit; Q++) {
+    int bits_per_mb_at_this_q;
+
+    err_correction_factor =
+      calc_correction_factor(err_per_mb, ERR_DIVISOR, 0.4, 0.90, Q) *
+      sr_correction * speed_correction *
+      cpi->twopass.est_max_qcorrection_factor;
+
+    if (err_correction_factor < 0.05)
+      err_correction_factor = 0.05;
+    else if (err_correction_factor > 5.0)
+      err_correction_factor = 5.0;
+
+    bits_per_mb_at_this_q =
+      vp9_bits_per_mb(INTER_FRAME, Q) + (int)overhead_bits_per_mb;
+
+    bits_per_mb_at_this_q = (int)(.5 + err_correction_factor *
+                                  (double)bits_per_mb_at_this_q);
+
+    // Mode and motion overhead
+    // As Q rises in real encode loop rd code will force overhead down
+    // We make a crude adjustment for this here as *.98 per Q step.
+    // PGW TODO.. This code is broken for the extended Q range
+    //            for now overhead set to 0.
+    // overhead_bits_per_mb = (int)((double)overhead_bits_per_mb * 0.98);
+
+    if (bits_per_mb_at_this_q <= target_norm_bits_per_mb)
+      break;
+  }
+
+  // Restriction on active max q for constrained quality mode.
+  if ((cpi->oxcf.end_usage == USAGE_CONSTRAINED_QUALITY) &&
+      (Q < cpi->cq_target_quality)) {
+    Q = cpi->cq_target_quality;
+  }
+
+  // Adjust maxq_min_limit and maxq_max_limit limits based on
+  // averaga q observed in clip for non kf/gf/arf frames
+  // Give average a chance to settle though.
+  // PGW TODO.. This code is broken for the extended Q range
+  if ((cpi->ni_frames >
+       ((int)cpi->twopass.total_stats->count >> 8)) &&
+      (cpi->ni_frames > 150)) {
+    adjust_maxq_qrange(cpi);
+  }
+
+  return Q;
+}
+
+// For cq mode estimate a cq level that matches the observed
+// complexity and data rate.
+static int estimate_cq(VP9_COMP *cpi,
+                       FIRSTPASS_STATS *fpstats,
+                       int section_target_bandwitdh,
+                       int overhead_bits) {
+  int Q;
+  int num_mbs = cpi->common.MBs;
+  int target_norm_bits_per_mb;
+
+  double section_err = (fpstats->coded_error / fpstats->count);
+  double err_per_mb = section_err / num_mbs;
+  double err_correction_factor;
+  double sr_err_diff;
+  double sr_correction;
+  double speed_correction = 1.0;
+  double clip_iiratio;
+  double clip_iifactor;
+  double overhead_bits_per_mb;
+
+
+  target_norm_bits_per_mb = (section_target_bandwitdh < (1 << 20))
+                            ? (512 * section_target_bandwitdh) / num_mbs
+                            : 512 * (section_target_bandwitdh / num_mbs);
+
+  // Estimate of overhead bits per mb
+  overhead_bits_per_mb = overhead_bits / num_mbs;
+
+  // Corrections for higher compression speed settings
+  // (reduced compression expected)
+  if (cpi->compressor_speed == 1) {
+    if (cpi->oxcf.cpu_used <= 5)
+      speed_correction = 1.04 + (cpi->oxcf.cpu_used * 0.04);
+    else
+      speed_correction = 1.25;
+  }
+
+  // Look at the drop in prediction quality between the last frame
+  // and the GF buffer (which contained an older frame).
+  sr_err_diff =
+    (fpstats->sr_coded_error - fpstats->coded_error) /
+    (fpstats->count * cpi->common.MBs);
+  sr_correction = (sr_err_diff / 32.0);
+  sr_correction = pow(sr_correction, 0.25);
+  if (sr_correction < 0.75)
+    sr_correction = 0.75;
+  else if (sr_correction > 1.25)
+    sr_correction = 1.25;
+
+  // II ratio correction factor for clip as a whole
+  clip_iiratio = cpi->twopass.total_stats->intra_error /
+                 DOUBLE_DIVIDE_CHECK(cpi->twopass.total_stats->coded_error);
+  clip_iifactor = 1.0 - ((clip_iiratio - 10.0) * 0.025);
+  if (clip_iifactor < 0.80)
+    clip_iifactor = 0.80;
+
+  // Try and pick a Q that can encode the content at the given rate.
+  for (Q = 0; Q < MAXQ; Q++) {
+    int bits_per_mb_at_this_q;
+
+    // Error per MB based correction factor
+    err_correction_factor =
+      calc_correction_factor(err_per_mb, 100.0, 0.4, 0.90, Q) *
+      sr_correction * speed_correction * clip_iifactor;
+
+    if (err_correction_factor < 0.05)
+      err_correction_factor = 0.05;
+    else if (err_correction_factor > 5.0)
+      err_correction_factor = 5.0;
+
+    bits_per_mb_at_this_q =
+      vp9_bits_per_mb(INTER_FRAME, Q) + (int)overhead_bits_per_mb;
+
+    bits_per_mb_at_this_q = (int)(.5 + err_correction_factor *
+                                  (double)bits_per_mb_at_this_q);
+
+    // Mode and motion overhead
+    // As Q rises in real encode loop rd code will force overhead down
+    // We make a crude adjustment for this here as *.98 per Q step.
+    // PGW TODO.. This code is broken for the extended Q range
+    //            for now overhead set to 0.
+    overhead_bits_per_mb = (int)((double)overhead_bits_per_mb * 0.98);
+
+    if (bits_per_mb_at_this_q <= target_norm_bits_per_mb)
+      break;
+  }
+
+  // Clip value to range "best allowed to (worst allowed - 1)"
+  Q = select_cq_level(Q);
+  if (Q >= cpi->worst_quality)
+    Q = cpi->worst_quality - 1;
+  if (Q < cpi->best_quality)
+    Q = cpi->best_quality;
+
+  return Q;
+}
+
+
+extern void vp9_new_frame_rate(VP9_COMP *cpi, double framerate);
+
+void vp9_init_second_pass(VP9_COMP *cpi) {
+  FIRSTPASS_STATS this_frame;
+  FIRSTPASS_STATS *start_pos;
+
+  double lower_bounds_min_rate = FRAME_OVERHEAD_BITS * cpi->oxcf.frame_rate;
+  double two_pass_min_rate = (double)(cpi->oxcf.target_bandwidth
+                                      * cpi->oxcf.two_pass_vbrmin_section / 100);
+
+  if (two_pass_min_rate < lower_bounds_min_rate)
+    two_pass_min_rate = lower_bounds_min_rate;
+
+  zero_stats(cpi->twopass.total_stats);
+  zero_stats(cpi->twopass.total_left_stats);
+
+  if (!cpi->twopass.stats_in_end)
+    return;
+
+  *cpi->twopass.total_stats = *cpi->twopass.stats_in_end;
+  *cpi->twopass.total_left_stats = *cpi->twopass.total_stats;
+
+  // each frame can have a different duration, as the frame rate in the source
+  // isn't guaranteed to be constant.   The frame rate prior to the first frame
+  // encoded in the second pass is a guess.  However the sum duration is not.
+  // Its calculated based on the actual durations of all frames from the first
+  // pass.
+  vp9_new_frame_rate(cpi,
+                     10000000.0 * cpi->twopass.total_stats->count /
+                     cpi->twopass.total_stats->duration);
+
+  cpi->output_frame_rate = cpi->oxcf.frame_rate;
+  cpi->twopass.bits_left = (int64_t)(cpi->twopass.total_stats->duration *
+                                     cpi->oxcf.target_bandwidth / 10000000.0);
+  cpi->twopass.bits_left -= (int64_t)(cpi->twopass.total_stats->duration *
+                                      two_pass_min_rate / 10000000.0);
+
+  // Calculate a minimum intra value to be used in determining the IIratio
+  // scores used in the second pass. We have this minimum to make sure
+  // that clips that are static but "low complexity" in the intra domain
+  // are still boosted appropriately for KF/GF/ARF
+  cpi->twopass.kf_intra_err_min = KF_MB_INTRA_MIN * cpi->common.MBs;
+  cpi->twopass.gf_intra_err_min = GF_MB_INTRA_MIN * cpi->common.MBs;
+
+  // This variable monitors how far behind the second ref update is lagging
+  cpi->twopass.sr_update_lag = 1;
+
+  // Scan the first pass file and calculate an average Intra / Inter error score ratio for the sequence
+  {
+    double sum_iiratio = 0.0;
+    double IIRatio;
+
+    start_pos = cpi->twopass.stats_in;               // Note starting "file" position
+
+    while (input_stats(cpi, &this_frame) != EOF) {
+      IIRatio = this_frame.intra_error / DOUBLE_DIVIDE_CHECK(this_frame.coded_error);
+      IIRatio = (IIRatio < 1.0) ? 1.0 : (IIRatio > 20.0) ? 20.0 : IIRatio;
+      sum_iiratio += IIRatio;
+    }
+
+    cpi->twopass.avg_iiratio = sum_iiratio / DOUBLE_DIVIDE_CHECK((double)cpi->twopass.total_stats->count);
+
+    // Reset file position
+    reset_fpf_position(cpi, start_pos);
+  }
+
+  // Scan the first pass file and calculate a modified total error based upon the bias/power function
+  // used to allocate bits
+  {
+    start_pos = cpi->twopass.stats_in;               // Note starting "file" position
+
+    cpi->twopass.modified_error_total = 0.0;
+    cpi->twopass.modified_error_used = 0.0;
+
+    while (input_stats(cpi, &this_frame) != EOF) {
+      cpi->twopass.modified_error_total += calculate_modified_err(cpi, &this_frame);
+    }
+    cpi->twopass.modified_error_left = cpi->twopass.modified_error_total;
+
+    reset_fpf_position(cpi, start_pos);            // Reset file position
+
+  }
+}
+
+void vp9_end_second_pass(VP9_COMP *cpi) {
+}
+
+// This function gives and estimate of how badly we believe
+// the prediction quality is decaying from frame to frame.
+static double get_prediction_decay_rate(VP9_COMP *cpi,
+                                        FIRSTPASS_STATS *next_frame) {
+  double prediction_decay_rate;
+  double second_ref_decay;
+  double mb_sr_err_diff;
+
+  // Initial basis is the % mbs inter coded
+  prediction_decay_rate = next_frame->pcnt_inter;
+
+  // Look at the observed drop in prediction quality between the last frame
+  // and the GF buffer (which contains an older frame).
+  mb_sr_err_diff =
+    (next_frame->sr_coded_error - next_frame->coded_error) /
+    (cpi->common.MBs);
+  second_ref_decay = 1.0 - (mb_sr_err_diff / 512.0);
+  second_ref_decay = pow(second_ref_decay, 0.5);
+  if (second_ref_decay < 0.85)
+    second_ref_decay = 0.85;
+  else if (second_ref_decay > 1.0)
+    second_ref_decay = 1.0;
+
+  if (second_ref_decay < prediction_decay_rate)
+    prediction_decay_rate = second_ref_decay;
+
+  return prediction_decay_rate;
+}
+
+// Function to test for a condition where a complex transition is followed
+// by a static section. For example in slide shows where there is a fade
+// between slides. This is to help with more optimal kf and gf positioning.
+static int detect_transition_to_still(
+  VP9_COMP *cpi,
+  int frame_interval,
+  int still_interval,
+  double loop_decay_rate,
+  double last_decay_rate) {
+  BOOL trans_to_still = FALSE;
+
+  // Break clause to detect very still sections after motion
+  // For example a static image after a fade or other transition
+  // instead of a clean scene cut.
+  if ((frame_interval > MIN_GF_INTERVAL) &&
+      (loop_decay_rate >= 0.999) &&
+      (last_decay_rate < 0.9)) {
+    int j;
+    FIRSTPASS_STATS *position = cpi->twopass.stats_in;
+    FIRSTPASS_STATS tmp_next_frame;
+    double zz_inter;
+
+    // Look ahead a few frames to see if static condition
+    // persists...
+    for (j = 0; j < still_interval; j++) {
+      if (EOF == input_stats(cpi, &tmp_next_frame))
+        break;
+
+      zz_inter =
+        (tmp_next_frame.pcnt_inter - tmp_next_frame.pcnt_motion);
+      if (zz_inter < 0.999)
+        break;
+    }
+    // Reset file position
+    reset_fpf_position(cpi, position);
+
+    // Only if it does do we signal a transition to still
+    if (j == still_interval)
+      trans_to_still = TRUE;
+  }
+
+  return trans_to_still;
+}
+
+// This function detects a flash through the high relative pcnt_second_ref
+// score in the frame following a flash frame. The offset passed in should
+// reflect this
+static BOOL detect_flash(VP9_COMP *cpi, int offset) {
+  FIRSTPASS_STATS next_frame;
+
+  BOOL flash_detected = FALSE;
+
+  // Read the frame data.
+  // The return is FALSE (no flash detected) if not a valid frame
+  if (read_frame_stats(cpi, &next_frame, offset) != EOF) {
+    // What we are looking for here is a situation where there is a
+    // brief break in prediction (such as a flash) but subsequent frames
+    // are reasonably well predicted by an earlier (pre flash) frame.
+    // The recovery after a flash is indicated by a high pcnt_second_ref
+    // comapred to pcnt_inter.
+    if ((next_frame.pcnt_second_ref > next_frame.pcnt_inter) &&
+        (next_frame.pcnt_second_ref >= 0.5)) {
+      flash_detected = TRUE;
+    }
+  }
+
+  return flash_detected;
+}
+
+// Update the motion related elements to the GF arf boost calculation
+static void accumulate_frame_motion_stats(
+  VP9_COMP *cpi,
+  FIRSTPASS_STATS *this_frame,
+  double *this_frame_mv_in_out,
+  double *mv_in_out_accumulator,
+  double *abs_mv_in_out_accumulator,
+  double *mv_ratio_accumulator) {
+  // double this_frame_mv_in_out;
+  double this_frame_mvr_ratio;
+  double this_frame_mvc_ratio;
+  double motion_pct;
+
+  // Accumulate motion stats.
+  motion_pct = this_frame->pcnt_motion;
+
+  // Accumulate Motion In/Out of frame stats
+  *this_frame_mv_in_out = this_frame->mv_in_out_count * motion_pct;
+  *mv_in_out_accumulator += this_frame->mv_in_out_count * motion_pct;
+  *abs_mv_in_out_accumulator +=
+    fabs(this_frame->mv_in_out_count * motion_pct);
+
+  // Accumulate a measure of how uniform (or conversely how random)
+  // the motion field is. (A ratio of absmv / mv)
+  if (motion_pct > 0.05) {
+    this_frame_mvr_ratio = fabs(this_frame->mvr_abs) /
+                           DOUBLE_DIVIDE_CHECK(fabs(this_frame->MVr));
+
+    this_frame_mvc_ratio = fabs(this_frame->mvc_abs) /
+                           DOUBLE_DIVIDE_CHECK(fabs(this_frame->MVc));
+
+    *mv_ratio_accumulator +=
+      (this_frame_mvr_ratio < this_frame->mvr_abs)
+      ? (this_frame_mvr_ratio * motion_pct)
+      : this_frame->mvr_abs * motion_pct;
+
+    *mv_ratio_accumulator +=
+      (this_frame_mvc_ratio < this_frame->mvc_abs)
+      ? (this_frame_mvc_ratio * motion_pct)
+      : this_frame->mvc_abs * motion_pct;
+
+  }
+}
+
+// Calculate a baseline boost number for the current frame.
+static double calc_frame_boost(
+  VP9_COMP *cpi,
+  FIRSTPASS_STATS *this_frame,
+  double this_frame_mv_in_out) {
+  double frame_boost;
+
+  // Underlying boost factor is based on inter intra error ratio
+  if (this_frame->intra_error > cpi->twopass.gf_intra_err_min)
+    frame_boost = (IIFACTOR * this_frame->intra_error /
+                   DOUBLE_DIVIDE_CHECK(this_frame->coded_error));
+  else
+    frame_boost = (IIFACTOR * cpi->twopass.gf_intra_err_min /
+                   DOUBLE_DIVIDE_CHECK(this_frame->coded_error));
+
+  // Increase boost for frames where new data coming into frame
+  // (eg zoom out). Slightly reduce boost if there is a net balance
+  // of motion out of the frame (zoom in).
+  // The range for this_frame_mv_in_out is -1.0 to +1.0
+  if (this_frame_mv_in_out > 0.0)
+    frame_boost += frame_boost * (this_frame_mv_in_out * 2.0);
+  // In extreme case boost is halved
+  else
+    frame_boost += frame_boost * (this_frame_mv_in_out / 2.0);
+
+  // Clip to maximum
+  if (frame_boost > GF_RMAX)
+    frame_boost = GF_RMAX;
+
+  return frame_boost;
+}
+
+static int calc_arf_boost(
+  VP9_COMP *cpi,
+  int offset,
+  int f_frames,
+  int b_frames,
+  int *f_boost,
+  int *b_boost) {
+  FIRSTPASS_STATS this_frame;
+
+  int i;
+  double boost_score = 0.0;
+  double mv_ratio_accumulator = 0.0;
+  double decay_accumulator = 1.0;
+  double this_frame_mv_in_out = 0.0;
+  double mv_in_out_accumulator = 0.0;
+  double abs_mv_in_out_accumulator = 0.0;
+  int arf_boost;
+  BOOL flash_detected = FALSE;
+
+  // Search forward from the proposed arf/next gf position
+  for (i = 0; i < f_frames; i++) {
+    if (read_frame_stats(cpi, &this_frame, (i + offset)) == EOF)
+      break;
+
+    // Update the motion related elements to the boost calculation
+    accumulate_frame_motion_stats(cpi, &this_frame,
+                                  &this_frame_mv_in_out, &mv_in_out_accumulator,
+                                  &abs_mv_in_out_accumulator, &mv_ratio_accumulator);
+
+    // We want to discount the the flash frame itself and the recovery
+    // frame that follows as both will have poor scores.
+    flash_detected = detect_flash(cpi, (i + offset)) ||
+                     detect_flash(cpi, (i + offset + 1));
+
+    // Cumulative effect of prediction quality decay
+    if (!flash_detected) {
+      decay_accumulator =
+        decay_accumulator *
+        get_prediction_decay_rate(cpi, &this_frame);
+      decay_accumulator =
+        decay_accumulator < 0.1 ? 0.1 : decay_accumulator;
+    }
+
+    boost_score += (decay_accumulator *
+                    calc_frame_boost(cpi, &this_frame, this_frame_mv_in_out));
+  }
+
+  *f_boost = (int)boost_score;
+
+  // Reset for backward looking loop
+  boost_score = 0.0;
+  mv_ratio_accumulator = 0.0;
+  decay_accumulator = 1.0;
+  this_frame_mv_in_out = 0.0;
+  mv_in_out_accumulator = 0.0;
+  abs_mv_in_out_accumulator = 0.0;
+
+  // Search backward towards last gf position
+  for (i = -1; i >= -b_frames; i--) {
+    if (read_frame_stats(cpi, &this_frame, (i + offset)) == EOF)
+      break;
+
+    // Update the motion related elements to the boost calculation
+    accumulate_frame_motion_stats(cpi, &this_frame,
+                                  &this_frame_mv_in_out, &mv_in_out_accumulator,
+                                  &abs_mv_in_out_accumulator, &mv_ratio_accumulator);
+
+    // We want to discount the the flash frame itself and the recovery
+    // frame that follows as both will have poor scores.
+    flash_detected = detect_flash(cpi, (i + offset)) ||
+                     detect_flash(cpi, (i + offset + 1));
+
+    // Cumulative effect of prediction quality decay
+    if (!flash_detected) {
+      decay_accumulator =
+        decay_accumulator *
+        get_prediction_decay_rate(cpi, &this_frame);
+      decay_accumulator =
+        decay_accumulator < 0.1 ? 0.1 : decay_accumulator;
+    }
+
+    boost_score += (decay_accumulator *
+                    calc_frame_boost(cpi, &this_frame, this_frame_mv_in_out));
+
+  }
+  *b_boost = (int)boost_score;
+
+  arf_boost = (*f_boost + *b_boost);
+  if (arf_boost < ((b_frames + f_frames) * 20))
+    arf_boost = ((b_frames + f_frames) * 20);
+
+  return arf_boost;
+}
+
+static void configure_arnr_filter(VP9_COMP *cpi, FIRSTPASS_STATS *this_frame) {
+  int half_gf_int;
+  int frames_after_arf;
+  int frames_bwd = cpi->oxcf.arnr_max_frames - 1;
+  int frames_fwd = cpi->oxcf.arnr_max_frames - 1;
+
+  // Define the arnr filter width for this group of frames:
+  // We only filter frames that lie within a distance of half
+  // the GF interval from the ARF frame. We also have to trap
+  // cases where the filter extends beyond the end of clip.
+  // Note: this_frame->frame has been updated in the loop
+  // so it now points at the ARF frame.
+  half_gf_int = cpi->baseline_gf_interval >> 1;
+  frames_after_arf = (int)(cpi->twopass.total_stats->count -
+                           this_frame->frame - 1);
+
+  switch (cpi->oxcf.arnr_type) {
+    case 1: // Backward filter
+      frames_fwd = 0;
+      if (frames_bwd > half_gf_int)
+        frames_bwd = half_gf_int;
+      break;
+
+    case 2: // Forward filter
+      if (frames_fwd > half_gf_int)
+        frames_fwd = half_gf_int;
+      if (frames_fwd > frames_after_arf)
+        frames_fwd = frames_after_arf;
+      frames_bwd = 0;
+      break;
+
+    case 3: // Centered filter
+    default:
+      frames_fwd >>= 1;
+      if (frames_fwd > frames_after_arf)
+        frames_fwd = frames_after_arf;
+      if (frames_fwd > half_gf_int)
+        frames_fwd = half_gf_int;
+
+      frames_bwd = frames_fwd;
+
+      // For even length filter there is one more frame backward
+      // than forward: e.g. len=6 ==> bbbAff, len=7 ==> bbbAfff.
+      if (frames_bwd < half_gf_int)
+        frames_bwd += (cpi->oxcf.arnr_max_frames + 1) & 0x1;
+      break;
+  }
+
+  cpi->active_arnr_frames = frames_bwd + 1 + frames_fwd;
+}
+
+// Analyse and define a gf/arf group .
+static void define_gf_group(VP9_COMP *cpi, FIRSTPASS_STATS *this_frame) {
+  FIRSTPASS_STATS next_frame;
+  FIRSTPASS_STATS *start_pos;
+  int i;
+  double boost_score = 0.0;
+  double old_boost_score = 0.0;
+  double gf_group_err = 0.0;
+  double gf_first_frame_err = 0.0;
+  double mod_frame_err = 0.0;
+
+  double mv_ratio_accumulator = 0.0;
+  double decay_accumulator = 1.0;
+  double zero_motion_accumulator = 1.0;
+
+  double loop_decay_rate = 1.00;          // Starting decay rate
+  double last_loop_decay_rate = 1.00;
+
+  double this_frame_mv_in_out = 0.0;
+  double mv_in_out_accumulator = 0.0;
+  double abs_mv_in_out_accumulator = 0.0;
+
+  int max_bits = frame_max_bits(cpi);     // Max for a single frame
+
+  unsigned int allow_alt_ref =
+    cpi->oxcf.play_alternate && cpi->oxcf.lag_in_frames;
+
+  int f_boost = 0;
+  int b_boost = 0;
+  BOOL flash_detected;
+
+  cpi->twopass.gf_group_bits = 0;
+
+  vp9_clear_system_state();  // __asm emms;
+
+  start_pos = cpi->twopass.stats_in;
+
+  vpx_memset(&next_frame, 0, sizeof(next_frame)); // assure clean
+
+  // Load stats for the current frame.
+  mod_frame_err = calculate_modified_err(cpi, this_frame);
+
+  // Note the error of the frame at the start of the group (this will be
+  // the GF frame error if we code a normal gf
+  gf_first_frame_err = mod_frame_err;
+
+  // Special treatment if the current frame is a key frame (which is also
+  // a gf). If it is then its error score (and hence bit allocation) need
+  // to be subtracted out from the calculation for the GF group
+  if (cpi->common.frame_type == KEY_FRAME)
+    gf_group_err -= gf_first_frame_err;
+
+  // Scan forward to try and work out how many frames the next gf group
+  // should contain and what level of boost is appropriate for the GF
+  // or ARF that will be coded with the group
+  i = 0;
+
+  while (((i < cpi->twopass.static_scene_max_gf_interval) ||
+          ((cpi->twopass.frames_to_key - i) < MIN_GF_INTERVAL)) &&
+         (i < cpi->twopass.frames_to_key)) {
+    i++;    // Increment the loop counter
+
+    // Accumulate error score of frames in this gf group
+    mod_frame_err = calculate_modified_err(cpi, this_frame);
+    gf_group_err += mod_frame_err;
+
+    if (EOF == input_stats(cpi, &next_frame))
+      break;
+
+    // Test for the case where there is a brief flash but the prediction
+    // quality back to an earlier frame is then restored.
+    flash_detected = detect_flash(cpi, 0);
+
+    // Update the motion related elements to the boost calculation
+    accumulate_frame_motion_stats(cpi, &next_frame,
+                                  &this_frame_mv_in_out, &mv_in_out_accumulator,
+                                  &abs_mv_in_out_accumulator, &mv_ratio_accumulator);
+
+    // Cumulative effect of prediction quality decay
+    if (!flash_detected) {
+      last_loop_decay_rate = loop_decay_rate;
+      loop_decay_rate = get_prediction_decay_rate(cpi, &next_frame);
+      decay_accumulator = decay_accumulator * loop_decay_rate;
+
+      // Monitor for static sections.
+      if ((next_frame.pcnt_inter - next_frame.pcnt_motion) <
+          zero_motion_accumulator) {
+        zero_motion_accumulator =
+          (next_frame.pcnt_inter - next_frame.pcnt_motion);
+      }
+
+      // Break clause to detect very still sections after motion
+      // (for example a staic image after a fade or other transition).
+      if (detect_transition_to_still(cpi, i, 5, loop_decay_rate,
+                                     last_loop_decay_rate)) {
+        allow_alt_ref = FALSE;
+        break;
+      }
+    }
+
+    // Calculate a boost number for this frame
+    boost_score +=
+      (decay_accumulator *
+       calc_frame_boost(cpi, &next_frame, this_frame_mv_in_out));
+
+    // Break out conditions.
+    if (
+      // Break at cpi->max_gf_interval unless almost totally static
+      (i >= cpi->max_gf_interval && (zero_motion_accumulator < 0.995)) ||
+      (
+        // Dont break out with a very short interval
+        (i > MIN_GF_INTERVAL) &&
+        // Dont break out very close to a key frame
+        ((cpi->twopass.frames_to_key - i) >= MIN_GF_INTERVAL) &&
+        ((boost_score > 125.0) || (next_frame.pcnt_inter < 0.75)) &&
+        (!flash_detected) &&
+        ((mv_ratio_accumulator > 100.0) ||
+         (abs_mv_in_out_accumulator > 3.0) ||
+         (mv_in_out_accumulator < -2.0) ||
+         ((boost_score - old_boost_score) < 12.5))
+      )) {
+      boost_score = old_boost_score;
+      break;
+    }
+
+    vpx_memcpy(this_frame, &next_frame, sizeof(*this_frame));
+
+    old_boost_score = boost_score;
+  }
+
+  // Dont allow a gf too near the next kf
+  if ((cpi->twopass.frames_to_key - i) < MIN_GF_INTERVAL) {
+    while (i < cpi->twopass.frames_to_key) {
+      i++;
+
+      if (EOF == input_stats(cpi, this_frame))
+        break;
+
+      if (i < cpi->twopass.frames_to_key) {
+        mod_frame_err = calculate_modified_err(cpi, this_frame);
+        gf_group_err += mod_frame_err;
+      }
+    }
+  }
+
+  // Set the interval till the next gf or arf.
+  cpi->baseline_gf_interval = i;
+
+  // Should we use the alternate refernce frame
+  if (allow_alt_ref &&
+      (i < cpi->oxcf.lag_in_frames) &&
+      (i >= MIN_GF_INTERVAL) &&
+      // dont use ARF very near next kf
+      (i <= (cpi->twopass.frames_to_key - MIN_GF_INTERVAL)) &&
+      ((next_frame.pcnt_inter > 0.75) ||
+       (next_frame.pcnt_second_ref > 0.5)) &&
+      ((mv_in_out_accumulator / (double)i > -0.2) ||
+       (mv_in_out_accumulator > -2.0)) &&
+      (boost_score > 100)) {
+    // Alterrnative boost calculation for alt ref
+    cpi->gfu_boost = calc_arf_boost(cpi, 0, (i - 1), (i - 1), &f_boost, &b_boost);
+    cpi->source_alt_ref_pending = TRUE;
+
+    configure_arnr_filter(cpi, this_frame);
+  } else {
+    cpi->gfu_boost = (int)boost_score;
+    cpi->source_alt_ref_pending = FALSE;
+  }
+
+  // Now decide how many bits should be allocated to the GF group as  a
+  // proportion of those remaining in the kf group.
+  // The final key frame group in the clip is treated as a special case
+  // where cpi->twopass.kf_group_bits is tied to cpi->twopass.bits_left.
+  // This is also important for short clips where there may only be one
+  // key frame.
+  if (cpi->twopass.frames_to_key >= (int)(cpi->twopass.total_stats->count -
+                                          cpi->common.current_video_frame)) {
+    cpi->twopass.kf_group_bits =
+      (cpi->twopass.bits_left > 0) ? cpi->twopass.bits_left : 0;
+  }
+
+  // Calculate the bits to be allocated to the group as a whole
+  if ((cpi->twopass.kf_group_bits > 0) &&
+      (cpi->twopass.kf_group_error_left > 0)) {
+    cpi->twopass.gf_group_bits =
+      (int)((double)cpi->twopass.kf_group_bits *
+            (gf_group_err / cpi->twopass.kf_group_error_left));
+  } else
+    cpi->twopass.gf_group_bits = 0;
+
+  cpi->twopass.gf_group_bits =
+    (cpi->twopass.gf_group_bits < 0)
+    ? 0
+    : (cpi->twopass.gf_group_bits > cpi->twopass.kf_group_bits)
+    ? cpi->twopass.kf_group_bits : cpi->twopass.gf_group_bits;
+
+  // Clip cpi->twopass.gf_group_bits based on user supplied data rate
+  // variability limit (cpi->oxcf.two_pass_vbrmax_section)
+  if (cpi->twopass.gf_group_bits > max_bits * cpi->baseline_gf_interval)
+    cpi->twopass.gf_group_bits = max_bits * cpi->baseline_gf_interval;
+
+  // Reset the file position
+  reset_fpf_position(cpi, start_pos);
+
+  // Update the record of error used so far (only done once per gf group)
+  cpi->twopass.modified_error_used += gf_group_err;
+
+  // Assign  bits to the arf or gf.
+  for (i = 0; i <= (cpi->source_alt_ref_pending && cpi->common.frame_type != KEY_FRAME); i++) {
+    int boost;
+    int allocation_chunks;
+    int Q = (cpi->oxcf.fixed_q < 0) ? cpi->last_q[INTER_FRAME] : cpi->oxcf.fixed_q;
+    int gf_bits;
+
+    boost = (cpi->gfu_boost * vp9_gfboost_qadjust(Q)) / 100;
+
+    // Set max and minimum boost and hence minimum allocation
+    if (boost > ((cpi->baseline_gf_interval + 1) * 200))
+      boost = ((cpi->baseline_gf_interval + 1) * 200);
+    else if (boost < 125)
+      boost = 125;
+
+    if (cpi->source_alt_ref_pending && i == 0)
+      allocation_chunks =
+        ((cpi->baseline_gf_interval + 1) * 100) + boost;
+    else
+      allocation_chunks =
+        (cpi->baseline_gf_interval * 100) + (boost - 100);
+
+    // Prevent overflow
+    if (boost > 1028) {
+      int divisor = boost >> 10;
+      boost /= divisor;
+      allocation_chunks /= divisor;
+    }
+
+    // Calculate the number of bits to be spent on the gf or arf based on
+    // the boost number
+    gf_bits = (int)((double)boost *
+                    (cpi->twopass.gf_group_bits /
+                     (double)allocation_chunks));
+
+    // If the frame that is to be boosted is simpler than the average for
+    // the gf/arf group then use an alternative calculation
+    // based on the error score of the frame itself
+    if (mod_frame_err < gf_group_err / (double)cpi->baseline_gf_interval) {
+      double  alt_gf_grp_bits;
+      int     alt_gf_bits;
+
+      alt_gf_grp_bits =
+        (double)cpi->twopass.kf_group_bits  *
+        (mod_frame_err * (double)cpi->baseline_gf_interval) /
+        DOUBLE_DIVIDE_CHECK(cpi->twopass.kf_group_error_left);
+
+      alt_gf_bits = (int)((double)boost * (alt_gf_grp_bits /
+                                           (double)allocation_chunks));
+
+      if (gf_bits > alt_gf_bits) {
+        gf_bits = alt_gf_bits;
+      }
+    }
+    // Else if it is harder than other frames in the group make sure it at
+    // least receives an allocation in keeping with its relative error
+    // score, otherwise it may be worse off than an "un-boosted" frame
+    else {
+      int alt_gf_bits =
+        (int)((double)cpi->twopass.kf_group_bits *
+              mod_frame_err /
+              DOUBLE_DIVIDE_CHECK(cpi->twopass.kf_group_error_left));
+
+      if (alt_gf_bits > gf_bits) {
+        gf_bits = alt_gf_bits;
+      }
+    }
+
+    // Dont allow a negative value for gf_bits
+    if (gf_bits < 0)
+      gf_bits = 0;
+
+    gf_bits += cpi->min_frame_bandwidth;                     // Add in minimum for a frame
+
+    if (i == 0) {
+      cpi->twopass.gf_bits = gf_bits;
+    }
+    if (i == 1 || (!cpi->source_alt_ref_pending && (cpi->common.frame_type != KEY_FRAME))) {
+      cpi->per_frame_bandwidth = gf_bits;                 // Per frame bit target for this frame
+    }
+  }
+
+  {
+    // Adjust KF group bits and error remainin
+    cpi->twopass.kf_group_error_left -= (int64_t)gf_group_err;
+    cpi->twopass.kf_group_bits -= cpi->twopass.gf_group_bits;
+
+    if (cpi->twopass.kf_group_bits < 0)
+      cpi->twopass.kf_group_bits = 0;
+
+    // Note the error score left in the remaining frames of the group.
+    // For normal GFs we want to remove the error score for the first frame
+    // of the group (except in Key frame case where this has already
+    // happened)
+    if (!cpi->source_alt_ref_pending && cpi->common.frame_type != KEY_FRAME)
+      cpi->twopass.gf_group_error_left = (int64_t)(gf_group_err
+                                                   - gf_first_frame_err);
+    else
+      cpi->twopass.gf_group_error_left = (int64_t)gf_group_err;
+
+    cpi->twopass.gf_group_bits -= cpi->twopass.gf_bits - cpi->min_frame_bandwidth;
+
+    if (cpi->twopass.gf_group_bits < 0)
+      cpi->twopass.gf_group_bits = 0;
+
+    // This condition could fail if there are two kfs very close together
+    // despite (MIN_GF_INTERVAL) and would cause a devide by 0 in the
+    // calculation of cpi->twopass.alt_extra_bits.
+    if (cpi->baseline_gf_interval >= 3) {
+      int boost = (cpi->source_alt_ref_pending)
+                  ? b_boost : cpi->gfu_boost;
+
+      if (boost >= 150) {
+        int pct_extra;
+
+        pct_extra = (boost - 100) / 50;
+        pct_extra = (pct_extra > 20) ? 20 : pct_extra;
+
+        cpi->twopass.alt_extra_bits = (int)
+          ((cpi->twopass.gf_group_bits * pct_extra) / 100);
+        cpi->twopass.gf_group_bits -= cpi->twopass.alt_extra_bits;
+        cpi->twopass.alt_extra_bits /=
+          ((cpi->baseline_gf_interval - 1) >> 1);
+      } else
+        cpi->twopass.alt_extra_bits = 0;
+    } else
+      cpi->twopass.alt_extra_bits = 0;
+  }
+
+  if (cpi->common.frame_type != KEY_FRAME) {
+    FIRSTPASS_STATS sectionstats;
+
+    zero_stats(&sectionstats);
+    reset_fpf_position(cpi, start_pos);
+
+    for (i = 0; i < cpi->baseline_gf_interval; i++) {
+      input_stats(cpi, &next_frame);
+      accumulate_stats(&sectionstats, &next_frame);
+    }
+
+    avg_stats(&sectionstats);
+
+    cpi->twopass.section_intra_rating = (int)
+      (sectionstats.intra_error /
+      DOUBLE_DIVIDE_CHECK(sectionstats.coded_error));
+
+    reset_fpf_position(cpi, start_pos);
+  }
+}
+
+// Allocate bits to a normal frame that is neither a gf an arf or a key frame.
+static void assign_std_frame_bits(VP9_COMP *cpi, FIRSTPASS_STATS *this_frame) {
+  int    target_frame_size;                                                             // gf_group_error_left
+
+  double modified_err;
+  double err_fraction;                                                                 // What portion of the remaining GF group error is used by this frame
+
+  int max_bits = frame_max_bits(cpi);    // Max for a single frame
+
+  // Calculate modified prediction error used in bit allocation
+  modified_err = calculate_modified_err(cpi, this_frame);
+
+  if (cpi->twopass.gf_group_error_left > 0)
+    err_fraction = modified_err / cpi->twopass.gf_group_error_left;                              // What portion of the remaining GF group error is used by this frame
+  else
+    err_fraction = 0.0;
+
+  target_frame_size = (int)((double)cpi->twopass.gf_group_bits * err_fraction);                    // How many of those bits available for allocation should we give it?
+
+  // Clip to target size to 0 - max_bits (or cpi->twopass.gf_group_bits) at the top end.
+  if (target_frame_size < 0)
+    target_frame_size = 0;
+  else {
+    if (target_frame_size > max_bits)
+      target_frame_size = max_bits;
+
+    if (target_frame_size > cpi->twopass.gf_group_bits)
+      target_frame_size = (int)cpi->twopass.gf_group_bits;
+  }
+
+  // Adjust error remaining
+  cpi->twopass.gf_group_error_left -= (int64_t)modified_err;
+  cpi->twopass.gf_group_bits -= target_frame_size;                                                // Adjust bits remaining
+
+  if (cpi->twopass.gf_group_bits < 0)
+    cpi->twopass.gf_group_bits = 0;
+
+  target_frame_size += cpi->min_frame_bandwidth;                                          // Add in the minimum number of bits that is set aside for every frame.
+
+
+  cpi->per_frame_bandwidth = target_frame_size;                                           // Per frame bit target for this frame
+}
+
+// Make a damped adjustment to the active max q.
+static int adjust_active_maxq(int old_maxqi, int new_maxqi) {
+  int i;
+  int ret_val = new_maxqi;
+  double old_q;
+  double new_q;
+  double target_q;
+
+  old_q = vp9_convert_qindex_to_q(old_maxqi);
+  new_q = vp9_convert_qindex_to_q(new_maxqi);
+
+  target_q = ((old_q * 7.0) + new_q) / 8.0;
+
+  if (target_q > old_q) {
+    for (i = old_maxqi; i <= new_maxqi; i++) {
+      if (vp9_convert_qindex_to_q(i) >= target_q) {
+        ret_val = i;
+        break;
+      }
+    }
+  } else {
+    for (i = old_maxqi; i >= new_maxqi; i--) {
+      if (vp9_convert_qindex_to_q(i) <= target_q) {
+        ret_val = i;
+        break;
+      }
+    }
+  }
+
+  return ret_val;
+}
+
+void vp9_second_pass(VP9_COMP *cpi) {
+  int tmp_q;
+  int frames_left = (int)(cpi->twopass.total_stats->count - cpi->common.current_video_frame);
+
+  FIRSTPASS_STATS this_frame;
+  FIRSTPASS_STATS this_frame_copy;
+
+  double this_frame_error;
+  double this_frame_intra_error;
+  double this_frame_coded_error;
+
+  FIRSTPASS_STATS *start_pos;
+
+  int overhead_bits;
+
+  if (!cpi->twopass.stats_in) {
+    return;
+  }
+
+  vp9_clear_system_state();
+
+  vpx_memset(&this_frame, 0, sizeof(FIRSTPASS_STATS));
+
+  if (EOF == input_stats(cpi, &this_frame))
+    return;
+
+  this_frame_error = this_frame.ssim_weighted_pred_err;
+  this_frame_intra_error = this_frame.intra_error;
+  this_frame_coded_error = this_frame.coded_error;
+
+  start_pos = cpi->twopass.stats_in;
+
+  // keyframe and section processing !
+  if (cpi->twopass.frames_to_key == 0) {
+    // Define next KF group and assign bits to it
+    vpx_memcpy(&this_frame_copy, &this_frame, sizeof(this_frame));
+    find_next_key_frame(cpi, &this_frame_copy);
+  }
+
+  // Is this a GF / ARF (Note that a KF is always also a GF)
+  if (cpi->frames_till_gf_update_due == 0) {
+    // Define next gf group and assign bits to it
+    vpx_memcpy(&this_frame_copy, &this_frame, sizeof(this_frame));
+    define_gf_group(cpi, &this_frame_copy);
+
+    // If we are going to code an altref frame at the end of the group and the current frame is not a key frame....
+    // If the previous group used an arf this frame has already benefited from that arf boost and it should not be given extra bits
+    // If the previous group was NOT coded using arf we may want to apply some boost to this GF as well
+    if (cpi->source_alt_ref_pending && (cpi->common.frame_type != KEY_FRAME)) {
+      // Assign a standard frames worth of bits from those allocated to the GF group
+      int bak = cpi->per_frame_bandwidth;
+      vpx_memcpy(&this_frame_copy, &this_frame, sizeof(this_frame));
+      assign_std_frame_bits(cpi, &this_frame_copy);
+      cpi->per_frame_bandwidth = bak;
+    }
+  }
+
+  // Otherwise this is an ordinary frame
+  else {
+    // Assign bits from those allocated to the GF group
+    vpx_memcpy(&this_frame_copy, &this_frame, sizeof(this_frame));
+    assign_std_frame_bits(cpi, &this_frame_copy);
+  }
+
+  // Keep a globally available copy of this and the next frame's iiratio.
+  cpi->twopass.this_iiratio = (int)(this_frame_intra_error /
+                              DOUBLE_DIVIDE_CHECK(this_frame_coded_error));
+  {
+    FIRSTPASS_STATS next_frame;
+    if (lookup_next_frame_stats(cpi, &next_frame) != EOF) {
+      cpi->twopass.next_iiratio = (int)(next_frame.intra_error /
+                                  DOUBLE_DIVIDE_CHECK(next_frame.coded_error));
+    }
+  }
+
+  // Set nominal per second bandwidth for this frame
+  cpi->target_bandwidth = (int)(cpi->per_frame_bandwidth
+                                * cpi->output_frame_rate);
+  if (cpi->target_bandwidth < 0)
+    cpi->target_bandwidth = 0;
+
+
+  // Account for mv, mode and other overheads.
+  overhead_bits = (int)estimate_modemvcost(
+                        cpi, cpi->twopass.total_left_stats);
+
+  // Special case code for first frame.
+  if (cpi->common.current_video_frame == 0) {
+    cpi->twopass.est_max_qcorrection_factor = 1.0;
+
+    // Set a cq_level in constrained quality mode.
+    if (cpi->oxcf.end_usage == USAGE_CONSTRAINED_QUALITY) {
+      int est_cq;
+
+      est_cq =
+        estimate_cq(cpi,
+                    cpi->twopass.total_left_stats,
+                    (int)(cpi->twopass.bits_left / frames_left),
+                    overhead_bits);
+
+      cpi->cq_target_quality = cpi->oxcf.cq_level;
+      if (est_cq > cpi->cq_target_quality)
+        cpi->cq_target_quality = est_cq;
+    }
+
+    // guess at maxq needed in 2nd pass
+    cpi->twopass.maxq_max_limit = cpi->worst_quality;
+    cpi->twopass.maxq_min_limit = cpi->best_quality;
+
+    tmp_q = estimate_max_q(
+              cpi,
+              cpi->twopass.total_left_stats,
+              (int)(cpi->twopass.bits_left / frames_left),
+              overhead_bits);
+
+    cpi->active_worst_quality         = tmp_q;
+    cpi->ni_av_qi                     = tmp_q;
+    cpi->avg_q                        = vp9_convert_qindex_to_q(tmp_q);
+
+    // Limit the maxq value returned subsequently.
+    // This increases the risk of overspend or underspend if the initial
+    // estimate for the clip is bad, but helps prevent excessive
+    // variation in Q, especially near the end of a clip
+    // where for example a small overspend may cause Q to crash
+    adjust_maxq_qrange(cpi);
+  }
+
+  // The last few frames of a clip almost always have to few or too many
+  // bits and for the sake of over exact rate control we dont want to make
+  // radical adjustments to the allowed quantizer range just to use up a
+  // few surplus bits or get beneath the target rate.
+  else if ((cpi->common.current_video_frame <
+            (((unsigned int)cpi->twopass.total_stats->count * 255) >> 8)) &&
+           ((cpi->common.current_video_frame + cpi->baseline_gf_interval) <
+            (unsigned int)cpi->twopass.total_stats->count)) {
+    if (frames_left < 1)
+      frames_left = 1;
+
+    tmp_q = estimate_max_q(
+              cpi,
+              cpi->twopass.total_left_stats,
+              (int)(cpi->twopass.bits_left / frames_left),
+              overhead_bits);
+
+    // Make a damped adjustment to active max Q
+    cpi->active_worst_quality =
+      adjust_active_maxq(cpi->active_worst_quality, tmp_q);
+  }
+
+  cpi->twopass.frames_to_key--;
+
+  // Update the total stats remaining sturcture
+  subtract_stats(cpi->twopass.total_left_stats, &this_frame);
+}
+
+
+static BOOL test_candidate_kf(VP9_COMP *cpi,  FIRSTPASS_STATS *last_frame, FIRSTPASS_STATS *this_frame, FIRSTPASS_STATS *next_frame) {
+  BOOL is_viable_kf = FALSE;
+
+  // Does the frame satisfy the primary criteria of a key frame
+  //      If so, then examine how well it predicts subsequent frames
+  if ((this_frame->pcnt_second_ref < 0.10) &&
+      (next_frame->pcnt_second_ref < 0.10) &&
+      ((this_frame->pcnt_inter < 0.05) ||
+       (
+         ((this_frame->pcnt_inter - this_frame->pcnt_neutral) < .35) &&
+         ((this_frame->intra_error / DOUBLE_DIVIDE_CHECK(this_frame->coded_error)) < 2.5) &&
+         ((fabs(last_frame->coded_error - this_frame->coded_error) / DOUBLE_DIVIDE_CHECK(this_frame->coded_error) > .40) ||
+          (fabs(last_frame->intra_error - this_frame->intra_error) / DOUBLE_DIVIDE_CHECK(this_frame->intra_error) > .40) ||
+          ((next_frame->intra_error / DOUBLE_DIVIDE_CHECK(next_frame->coded_error)) > 3.5)
+         )
+       )
+      )
+     ) {
+    int i;
+    FIRSTPASS_STATS *start_pos;
+
+    FIRSTPASS_STATS local_next_frame;
+
+    double boost_score = 0.0;
+    double old_boost_score = 0.0;
+    double decay_accumulator = 1.0;
+    double next_iiratio;
+
+    vpx_memcpy(&local_next_frame, next_frame, sizeof(*next_frame));
+
+    // Note the starting file position so we can reset to it
+    start_pos = cpi->twopass.stats_in;
+
+    // Examine how well the key frame predicts subsequent frames
+    for (i = 0; i < 16; i++) {
+      next_iiratio = (IIKFACTOR1 * local_next_frame.intra_error / DOUBLE_DIVIDE_CHECK(local_next_frame.coded_error));
+
+      if (next_iiratio > RMAX)
+        next_iiratio = RMAX;
+
+      // Cumulative effect of decay in prediction quality
+      if (local_next_frame.pcnt_inter > 0.85)
+        decay_accumulator = decay_accumulator * local_next_frame.pcnt_inter;
+      else
+        decay_accumulator = decay_accumulator * ((0.85 + local_next_frame.pcnt_inter) / 2.0);
+
+      // decay_accumulator = decay_accumulator * local_next_frame.pcnt_inter;
+
+      // Keep a running total
+      boost_score += (decay_accumulator * next_iiratio);
+
+      // Test various breakout clauses
+      if ((local_next_frame.pcnt_inter < 0.05) ||
+          (next_iiratio < 1.5) ||
+          (((local_next_frame.pcnt_inter -
+             local_next_frame.pcnt_neutral) < 0.20) &&
+           (next_iiratio < 3.0)) ||
+          ((boost_score - old_boost_score) < 3.0) ||
+          (local_next_frame.intra_error < 200)
+         ) {
+        break;
+      }
+
+      old_boost_score = boost_score;
+
+      // Get the next frame details
+      if (EOF == input_stats(cpi, &local_next_frame))
+        break;
+    }
+
+    // If there is tolerable prediction for at least the next 3 frames then break out else discard this pottential key frame and move on
+    if (boost_score > 30.0 && (i > 3))
+      is_viable_kf = TRUE;
+    else {
+      // Reset the file position
+      reset_fpf_position(cpi, start_pos);
+
+      is_viable_kf = FALSE;
+    }
+  }
+
+  return is_viable_kf;
+}
+static void find_next_key_frame(VP9_COMP *cpi, FIRSTPASS_STATS *this_frame) {
+  int i, j;
+  FIRSTPASS_STATS last_frame;
+  FIRSTPASS_STATS first_frame;
+  FIRSTPASS_STATS next_frame;
+  FIRSTPASS_STATS *start_position;
+
+  double decay_accumulator = 1.0;
+  double zero_motion_accumulator = 1.0;
+  double boost_score = 0;
+  double old_boost_score = 0.0;
+  double loop_decay_rate;
+
+  double kf_mod_err = 0.0;
+  double kf_group_err = 0.0;
+  double kf_group_intra_err = 0.0;
+  double kf_group_coded_err = 0.0;
+  double recent_loop_decay[8] = {1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0};
+
+  vpx_memset(&next_frame, 0, sizeof(next_frame)); // assure clean
+
+  vp9_clear_system_state();  // __asm emms;
+  start_position = cpi->twopass.stats_in;
+
+  cpi->common.frame_type = KEY_FRAME;
+
+  // is this a forced key frame by interval
+  cpi->this_key_frame_forced = cpi->next_key_frame_forced;
+
+  // Clear the alt ref active flag as this can never be active on a key frame
+  cpi->source_alt_ref_active = FALSE;
+
+  // Kf is always a gf so clear frames till next gf counter
+  cpi->frames_till_gf_update_due = 0;
+
+  cpi->twopass.frames_to_key = 1;
+
+  // Take a copy of the initial frame details
+  vpx_memcpy(&first_frame, this_frame, sizeof(*this_frame));
+
+  cpi->twopass.kf_group_bits = 0;        // Total bits avaialable to kf group
+  cpi->twopass.kf_group_error_left = 0;  // Group modified error score.
+
+  kf_mod_err = calculate_modified_err(cpi, this_frame);
+
+  // find the next keyframe
+  i = 0;
+  while (cpi->twopass.stats_in < cpi->twopass.stats_in_end) {
+    // Accumulate kf group error
+    kf_group_err += calculate_modified_err(cpi, this_frame);
+
+    // These figures keep intra and coded error counts for all frames including key frames in the group.
+    // The effect of the key frame itself can be subtracted out using the first_frame data collected above
+    kf_group_intra_err += this_frame->intra_error;
+    kf_group_coded_err += this_frame->coded_error;
+
+    // load a the next frame's stats
+    vpx_memcpy(&last_frame, this_frame, sizeof(*this_frame));
+    input_stats(cpi, this_frame);
+
+    // Provided that we are not at the end of the file...
+    if (cpi->oxcf.auto_key
+        && lookup_next_frame_stats(cpi, &next_frame) != EOF) {
+      // Normal scene cut check
+      if (test_candidate_kf(cpi, &last_frame, this_frame, &next_frame)) {
+        break;
+      }
+
+      // How fast is prediction quality decaying
+      loop_decay_rate = get_prediction_decay_rate(cpi, &next_frame);
+
+      // We want to know something about the recent past... rather than
+      // as used elsewhere where we are concened with decay in prediction
+      // quality since the last GF or KF.
+      recent_loop_decay[i % 8] = loop_decay_rate;
+      decay_accumulator = 1.0;
+      for (j = 0; j < 8; j++) {
+        decay_accumulator = decay_accumulator * recent_loop_decay[j];
+      }
+
+      // Special check for transition or high motion followed by a
+      // to a static scene.
+      if (detect_transition_to_still(cpi, i,
+                                     (cpi->key_frame_frequency - i),
+                                     loop_decay_rate,
+                                     decay_accumulator)) {
+        break;
+      }
+
+
+      // Step on to the next frame
+      cpi->twopass.frames_to_key++;
+
+      // If we don't have a real key frame within the next two
+      // forcekeyframeevery intervals then break out of the loop.
+      if (cpi->twopass.frames_to_key >= 2 * (int)cpi->key_frame_frequency)
+        break;
+    } else
+      cpi->twopass.frames_to_key++;
+
+    i++;
+  }
+
+  // If there is a max kf interval set by the user we must obey it.
+  // We already breakout of the loop above at 2x max.
+  // This code centers the extra kf if the actual natural
+  // interval is between 1x and 2x
+  if (cpi->oxcf.auto_key
+      && cpi->twopass.frames_to_key > (int)cpi->key_frame_frequency) {
+    FIRSTPASS_STATS *current_pos = cpi->twopass.stats_in;
+    FIRSTPASS_STATS tmp_frame;
+
+    cpi->twopass.frames_to_key /= 2;
+
+    // Copy first frame details
+    vpx_memcpy(&tmp_frame, &first_frame, sizeof(first_frame));
+
+    // Reset to the start of the group
+    reset_fpf_position(cpi, start_position);
+
+    kf_group_err = 0;
+    kf_group_intra_err = 0;
+    kf_group_coded_err = 0;
+
+    // Rescan to get the correct error data for the forced kf group
+    for (i = 0; i < cpi->twopass.frames_to_key; i++) {
+      // Accumulate kf group errors
+      kf_group_err += calculate_modified_err(cpi, &tmp_frame);
+      kf_group_intra_err += tmp_frame.intra_error;
+      kf_group_coded_err += tmp_frame.coded_error;
+
+      // Load a the next frame's stats
+      input_stats(cpi, &tmp_frame);
+    }
+
+    // Reset to the start of the group
+    reset_fpf_position(cpi, current_pos);
+
+    cpi->next_key_frame_forced = TRUE;
+  } else
+    cpi->next_key_frame_forced = FALSE;
+
+  // Special case for the last frame of the file
+  if (cpi->twopass.stats_in >= cpi->twopass.stats_in_end) {
+    // Accumulate kf group error
+    kf_group_err += calculate_modified_err(cpi, this_frame);
+
+    // These figures keep intra and coded error counts for all frames including key frames in the group.
+    // The effect of the key frame itself can be subtracted out using the first_frame data collected above
+    kf_group_intra_err += this_frame->intra_error;
+    kf_group_coded_err += this_frame->coded_error;
+  }
+
+  // Calculate the number of bits that should be assigned to the kf group.
+  if ((cpi->twopass.bits_left > 0) && (cpi->twopass.modified_error_left > 0.0)) {
+    // Max for a single normal frame (not key frame)
+    int max_bits = frame_max_bits(cpi);
+
+    // Maximum bits for the kf group
+    int64_t max_grp_bits;
+
+    // Default allocation based on bits left and relative
+    // complexity of the section
+    cpi->twopass.kf_group_bits = (int64_t)(cpi->twopass.bits_left *
+                                           (kf_group_err /
+                                            cpi->twopass.modified_error_left));
+
+    // Clip based on maximum per frame rate defined by the user.
+    max_grp_bits = (int64_t)max_bits * (int64_t)cpi->twopass.frames_to_key;
+    if (cpi->twopass.kf_group_bits > max_grp_bits)
+      cpi->twopass.kf_group_bits = max_grp_bits;
+  } else
+    cpi->twopass.kf_group_bits = 0;
+
+  // Reset the first pass file position
+  reset_fpf_position(cpi, start_position);
+
+  // determine how big to make this keyframe based on how well the subsequent frames use inter blocks
+  decay_accumulator = 1.0;
+  boost_score = 0.0;
+  loop_decay_rate = 1.00;       // Starting decay rate
+
+  for (i = 0; i < cpi->twopass.frames_to_key; i++) {
+    double r;
+
+    if (EOF == input_stats(cpi, &next_frame))
+      break;
+
+    if (next_frame.intra_error > cpi->twopass.kf_intra_err_min)
+      r = (IIKFACTOR2 * next_frame.intra_error /
+           DOUBLE_DIVIDE_CHECK(next_frame.coded_error));
+    else
+      r = (IIKFACTOR2 * cpi->twopass.kf_intra_err_min /
+           DOUBLE_DIVIDE_CHECK(next_frame.coded_error));
+
+    if (r > RMAX)
+      r = RMAX;
+
+    // Monitor for static sections.
+    if ((next_frame.pcnt_inter - next_frame.pcnt_motion) <
+        zero_motion_accumulator) {
+      zero_motion_accumulator =
+        (next_frame.pcnt_inter - next_frame.pcnt_motion);
+    }
+
+    // How fast is prediction quality decaying
+    if (!detect_flash(cpi, 0)) {
+      loop_decay_rate = get_prediction_decay_rate(cpi, &next_frame);
+      decay_accumulator = decay_accumulator * loop_decay_rate;
+      decay_accumulator = decay_accumulator < 0.1 ? 0.1 : decay_accumulator;
+    }
+
+    boost_score += (decay_accumulator * r);
+
+    if ((i > MIN_GF_INTERVAL) &&
+        ((boost_score - old_boost_score) < 6.25)) {
+      break;
+    }
+
+    old_boost_score = boost_score;
+  }
+
+  {
+    FIRSTPASS_STATS sectionstats;
+
+    zero_stats(&sectionstats);
+    reset_fpf_position(cpi, start_position);
+
+    for (i = 0; i < cpi->twopass.frames_to_key; i++) {
+      input_stats(cpi, &next_frame);
+      accumulate_stats(&sectionstats, &next_frame);
+    }
+
+    avg_stats(&sectionstats);
+
+    cpi->twopass.section_intra_rating = (int)
+      (sectionstats.intra_error
+      / DOUBLE_DIVIDE_CHECK(sectionstats.coded_error));
+  }
+
+  // Reset the first pass file position
+  reset_fpf_position(cpi, start_position);
+
+  // Work out how many bits to allocate for the key frame itself
+  if (1) {
+    int kf_boost = (int)boost_score;
+    int allocation_chunks;
+    int alt_kf_bits;
+
+    if (kf_boost < 300) {
+      kf_boost += (cpi->twopass.frames_to_key * 3);
+      if (kf_boost > 300)
+        kf_boost = 300;
+    }
+
+    if (kf_boost < 250)                                                      // Min KF boost
+      kf_boost = 250;
+
+    // Make a note of baseline boost and the zero motion
+    // accumulator value for use elsewhere.
+    cpi->kf_boost = kf_boost;
+    cpi->kf_zeromotion_pct = (int)(zero_motion_accumulator * 100.0);
+
+    // We do three calculations for kf size.
+    // The first is based on the error score for the whole kf group.
+    // The second (optionaly) on the key frames own error if this is
+    // smaller than the average for the group.
+    // The final one insures that the frame receives at least the
+    // allocation it would have received based on its own error score vs
+    // the error score remaining
+    // Special case if the sequence appears almost totaly static
+    // In this case we want to spend almost all of the bits on the
+    // key frame.
+    // cpi->twopass.frames_to_key-1 because key frame itself is taken
+    // care of by kf_boost.
+    if (zero_motion_accumulator >= 0.99) {
+      allocation_chunks =
+        ((cpi->twopass.frames_to_key - 1) * 10) + kf_boost;
+    } else {
+      allocation_chunks =
+        ((cpi->twopass.frames_to_key - 1) * 100) + kf_boost;
+    }
+
+    // Prevent overflow
+    if (kf_boost > 1028) {
+      int divisor = kf_boost >> 10;
+      kf_boost /= divisor;
+      allocation_chunks /= divisor;
+    }
+
+    cpi->twopass.kf_group_bits = (cpi->twopass.kf_group_bits < 0) ? 0 : cpi->twopass.kf_group_bits;
+
+    // Calculate the number of bits to be spent on the key frame
+    cpi->twopass.kf_bits  = (int)((double)kf_boost * ((double)cpi->twopass.kf_group_bits / (double)allocation_chunks));
+
+    // If the key frame is actually easier than the average for the
+    // kf group (which does sometimes happen... eg a blank intro frame)
+    // Then use an alternate calculation based on the kf error score
+    // which should give a smaller key frame.
+    if (kf_mod_err < kf_group_err / cpi->twopass.frames_to_key) {
+      double  alt_kf_grp_bits =
+        ((double)cpi->twopass.bits_left *
+         (kf_mod_err * (double)cpi->twopass.frames_to_key) /
+         DOUBLE_DIVIDE_CHECK(cpi->twopass.modified_error_left));
+
+      alt_kf_bits = (int)((double)kf_boost *
+                          (alt_kf_grp_bits / (double)allocation_chunks));
+
+      if (cpi->twopass.kf_bits > alt_kf_bits) {
+        cpi->twopass.kf_bits = alt_kf_bits;
+      }
+    }
+    // Else if it is much harder than other frames in the group make sure
+    // it at least receives an allocation in keeping with its relative
+    // error score
+    else {
+      alt_kf_bits =
+        (int)((double)cpi->twopass.bits_left *
+              (kf_mod_err /
+               DOUBLE_DIVIDE_CHECK(cpi->twopass.modified_error_left)));
+
+      if (alt_kf_bits > cpi->twopass.kf_bits) {
+        cpi->twopass.kf_bits = alt_kf_bits;
+      }
+    }
+
+    cpi->twopass.kf_group_bits -= cpi->twopass.kf_bits;
+    // Add in the minimum frame allowance
+    cpi->twopass.kf_bits += cpi->min_frame_bandwidth;
+
+    // Peer frame bit target for this frame
+    cpi->per_frame_bandwidth = cpi->twopass.kf_bits;
+    // Convert to a per second bitrate
+    cpi->target_bandwidth = (int)(cpi->twopass.kf_bits *
+                                  cpi->output_frame_rate);
+  }
+
+  // Note the total error score of the kf group minus the key frame itself
+  cpi->twopass.kf_group_error_left = (int)(kf_group_err - kf_mod_err);
+
+  // Adjust the count of total modified error left.
+  // The count of bits left is adjusted elsewhere based on real coded frame sizes
+  cpi->twopass.modified_error_left -= kf_group_err;
+}