libvpx: Pull from upstream

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 <limits.h>
 #include <math.h>
-#include <limits.h>
 #include <stdio.h>
+
+#include "./vpx_scale_rtcd.h"
+
+#include "vpx_mem/vpx_mem.h"
+#include "vpx_scale/vpx_scale.h"
+#include "vpx_scale/yv12config.h"
+
+#include "vp9/common/vp9_entropymv.h"
+#include "vp9/common/vp9_quant_common.h"
+#include "vp9/common/vp9_reconinter.h"  // setup_dst_planes()
 #include "vp9/common/vp9_systemdependent.h"
+
 #include "vp9/encoder/vp9_block.h"
 #include "vp9/encoder/vp9_encodeframe.h"
 #include "vp9/encoder/vp9_encodemb.h"
+#include "vp9/encoder/vp9_encodemv.h"
 #include "vp9/encoder/vp9_extend.h"
 #include "vp9/encoder/vp9_firstpass.h"
 #include "vp9/encoder/vp9_mcomp.h"
 #include "vp9/encoder/vp9_onyx_int.h"
+#include "vp9/encoder/vp9_quantize.h"
+#include "vp9/encoder/vp9_ratectrl.h"
+#include "vp9/encoder/vp9_rdopt.h"
+#include "vp9/encoder/vp9_vaq.h"
 #include "vp9/encoder/vp9_variance.h"
-#include "vpx_scale/vpx_scale.h"
-#include "vpx_mem/vpx_mem.h"
-#include "vpx_scale/yv12config.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 "vp9/encoder/vp9_vaq.h"
-#include "./vpx_scale_rtcd.h"
-// TODO(jkoleszar): for setup_dst_planes
-#include "vp9/common/vp9_reconinter.h"
 
 #define OUTPUT_FPF 0
 
 #define IIFACTOR   12.5
 #define IIKFACTOR1 12.5
 #define IIKFACTOR2 15.0
 #define RMAX       512.0
 #define GF_RMAX    96.0
 #define ERR_DIVISOR   150.0
 #define MIN_DECAY_FACTOR 0.1
@@ skipping 12 matching lines @@
   *a = *b;
   *b = temp;
 }
 
 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++) {
+  for (i = 0; i < QINDEX_RANGE; ++i) {
     if (target_q <= vp9_convert_qindex_to_q(i)) {
       ret_val = i;
       break;
     }
   }
 
   return ret_val;
 }
 
 static int gfboost_qadjust(int qindex) {
@@ skipping 20 matching lines @@
 static int lookup_next_frame_stats(const struct twopass_rc *p,
                                    FIRSTPASS_STATS *next_frame) {
   if (p->stats_in >= p->stats_in_end)
     return EOF;
 
   *next_frame = *p->stats_in;
   return 1;
 }
 
 
-// Read frame stats at an offset from the current position
+// Read frame stats at an offset from the current position.
 static int read_frame_stats(const struct twopass_rc *p,
                             FIRSTPASS_STATS *frame_stats, int offset) {
   const FIRSTPASS_STATS *fps_ptr = p->stats_in;
 
-  // Check legality of offset
+  // Check legality of offset.
   if (offset >= 0) {
     if (&fps_ptr[offset] >= p->stats_in_end)
       return EOF;
   } else if (offset < 0) {
     if (&fps_ptr[offset] < p->stats_in_start)
       return EOF;
   }
 
   *frame_stats = fps_ptr[offset];
   return 1;
 }
 
 static int input_stats(struct twopass_rc *p, FIRSTPASS_STATS *fps) {
   if (p->stats_in >= p->stats_in_end)
     return EOF;
 
   *fps = *p->stats_in;
   ++p->stats_in;
   return 1;
 }
 
-static void output_stats(const VP9_COMP *cpi,
-                         struct vpx_codec_pkt_list *pktlist,
-                         FIRSTPASS_STATS *stats) {
+static void output_stats(FIRSTPASS_STATS *stats,
+                         struct vpx_codec_pkt_list *pktlist) {
   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,
@@ skipping 190 matching lines @@
     max_bits = cpi->rc.max_frame_bandwidth;
 
   return (int)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);
+  output_stats(&cpi->twopass.total_stats, cpi->output_pkt_list);
 }
 
 static vp9_variance_fn_t get_block_variance_fn(BLOCK_SIZE bsize) {
   switch (bsize) {
     case BLOCK_8X8:
       return vp9_mse8x8;
     case BLOCK_16X8:
       return vp9_mse16x8;
     case BLOCK_8X16:
       return vp9_mse8x16;
     default:
       return vp9_mse16x16;
   }
 }
 
-static unsigned int zz_motion_search(const VP9_COMP *cpi, const MACROBLOCK *x) {
+static unsigned int zz_motion_search(const MACROBLOCK *x) {
   const MACROBLOCKD *const xd = &x->e_mbd;
   const uint8_t *const src = x->plane[0].src.buf;
   const int src_stride = x->plane[0].src.stride;
   const uint8_t *const ref = xd->plane[0].pre[0].buf;
   const int ref_stride = xd->plane[0].pre[0].stride;
-
   unsigned int sse;
   vp9_variance_fn_t fn = get_block_variance_fn(xd->mi_8x8[0]->mbmi.sb_type);
   fn(src, src_stride, ref, ref_stride, &sse);
   return sse;
 }
 
 static void first_pass_motion_search(VP9_COMP *cpi, MACROBLOCK *x,
                                      const MV *ref_mv, MV *best_mv,
                                      int *best_motion_err) {
   MACROBLOCKD *const xd = &x->e_mbd;
   MV tmp_mv = {0, 0};
   MV ref_mv_full = {ref_mv->row >> 3, ref_mv->col >> 3};
   int num00, tmp_err, n, sr = 0;
   int step_param = 3;
   int further_steps = (MAX_MVSEARCH_STEPS - 1) - step_param;
   const BLOCK_SIZE bsize = xd->mi_8x8[0]->mbmi.sb_type;
   vp9_variance_fn_ptr_t v_fn_ptr = cpi->fn_ptr[bsize];
   int new_mv_mode_penalty = 256;
   const int quart_frm = MIN(cpi->common.width, cpi->common.height);
 
-  // refine the motion search range accroding to the frame dimension
-  // for first pass test
+  // Refine the motion search range according to the frame dimension
+  // for first pass test.
   while ((quart_frm << sr) < MAX_FULL_PEL_VAL)
-    sr++;
+    ++sr;
 
   step_param += sr;
   further_steps -= sr;
 
-  // override the default variance function to use MSE
+  // Override the default variance function to use MSE.
   v_fn_ptr.vf = get_block_variance_fn(bsize);
 
-  // Initial step/diamond search centred on best mv
+  // Center the initial step/diamond search on best mv.
   tmp_err = cpi->diamond_search_sad(x, &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.row;
     best_mv->col = tmp_mv.col;
   }
 
-  // Further step/diamond searches as necessary
+  // Carry out further step/diamond searches as necessary.
   n = num00;
   num00 = 0;
 
   while (n < further_steps) {
-    n++;
+    ++n;
 
     if (num00) {
-      num00--;
+      --num00;
     } else {
       tmp_err = cpi->diamond_search_sad(x, &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) {
@@ skipping 44 matching lines @@
   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;
   struct twopass_rc *const twopass = &cpi->twopass;
   const MV zero_mv = {0, 0};
 
-  vp9_clear_system_state();  // __asm emms;
+  vp9_clear_system_state();
 
   vp9_setup_src_planes(x, cpi->Source, 0, 0);
   setup_pre_planes(xd, 0, lst_yv12, 0, 0, NULL);
   setup_dst_planes(xd, new_yv12, 0, 0);
 
   xd->mi_8x8 = cm->mi_grid_visible;
-  xd->mi_8x8[0] = cm->mi;  // required for vp9_frame_init_quantizer
+  xd->mi_8x8[0] = cm->mi;
 
   vp9_setup_block_planes(&x->e_mbd, cm->subsampling_x, cm->subsampling_y);
 
   vp9_frame_init_quantizer(cpi);
 
   for (i = 0; i < MAX_MB_PLANE; ++i) {
     p[i].coeff = ctx->coeff_pbuf[i][1];
     p[i].qcoeff = ctx->qcoeff_pbuf[i][1];
     pd[i].dqcoeff = ctx->dqcoeff_pbuf[i][1];
     p[i].eobs = ctx->eobs_pbuf[i][1];
   }
   x->skip_recode = 0;
 
   vp9_init_mv_probs(cm);
   vp9_initialize_rd_consts(cpi);
 
-  // tiling is ignored in the first pass
+  // Tiling is ignored in the first pass.
   vp9_tile_init(&tile, cm, 0, 0);
 
-  // for each macroblock row in image
-  for (mb_row = 0; mb_row < cm->mb_rows; mb_row++) {
+  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
+    // 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 * uv_mb_height);
 
     // Set up limit values for motion vectors to prevent them extending
-    // outside the UMV borders
+    // outside the UMV borders.
     x->mv_row_min = -((mb_row * 16) + BORDER_MV_PIXELS_B16);
     x->mv_row_max = ((cm->mb_rows - 1 - mb_row) * 16)
                     + BORDER_MV_PIXELS_B16;
 
-    // for each macroblock col in image
-    for (mb_col = 0; mb_col < cm->mb_cols; mb_col++) {
+    for (mb_col = 0; mb_col < cm->mb_cols; ++mb_col) {
       int this_error;
       const int use_dc_pred = (mb_col || mb_row) && (!mb_col || !mb_row);
       double error_weight = 1.0;
       const BLOCK_SIZE bsize = get_bsize(cm, mb_row, mb_col);
 
-      vp9_clear_system_state();  // __asm emms;
+      vp9_clear_system_state();
 
       xd->plane[0].dst.buf = new_yv12->y_buffer + recon_yoffset;
       xd->plane[1].dst.buf = new_yv12->u_buffer + recon_uvoffset;
       xd->plane[2].dst.buf = new_yv12->v_buffer + recon_uvoffset;
       xd->left_available = (mb_col != 0);
       xd->mi_8x8[0]->mbmi.sb_type = bsize;
       xd->mi_8x8[0]->mbmi.ref_frame[0] = INTRA_FRAME;
       set_mi_row_col(xd, &tile,
                      mb_row << 1, num_8x8_blocks_high_lookup[bsize],
                      mb_col << 1, num_8x8_blocks_wide_lookup[bsize],
                      cm->mi_rows, cm->mi_cols);
 
       if (cpi->oxcf.aq_mode == VARIANCE_AQ) {
         const int energy = vp9_block_energy(cpi, x, bsize);
         error_weight = vp9_vaq_inv_q_ratio(energy);
       }
 
-      // do intra 16x16 prediction
+      // Do intra 16x16 prediction.
       this_error = vp9_encode_intra(x, use_dc_pred);
       if (cpi->oxcf.aq_mode == VARIANCE_AQ) {
-        vp9_clear_system_state();  // __asm emms;
-        this_error *= error_weight;
+        vp9_clear_system_state();
+        this_error = (int)(this_error * error_weight);
       }
 
-      // intrapenalty below deals with situations where the intra and inter
-      // error scores are very low (eg a plain black frame).
+      // Intrapenalty below deals with situations where the intra and inter
+      // error scores are very low (e.g. 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 for 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
+      // Accumulate the intra error.
       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) + BORDER_MV_PIXELS_B16);
       x->mv_col_max = ((cm->mb_cols - 1 - mb_col) * 16) + BORDER_MV_PIXELS_B16;
 
-      // Other than for the first frame do a motion search
+      // Other than for the first frame do a motion search.
       if (cm->current_video_frame > 0) {
         int tmp_err, motion_error;
         int_mv mv, tmp_mv;
 
         xd->plane[0].pre[0].buf = lst_yv12->y_buffer + recon_yoffset;
-        motion_error = zz_motion_search(cpi, x);
-        // Simple 0,0 motion with no mv overhead
+        motion_error = zz_motion_search(x);
+        // Assume 0,0 motion with no mv overhead.
         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
+        // starting point (best reference) for the search.
         first_pass_motion_search(cpi, x, &best_ref_mv.as_mv, &mv.as_mv,
                                  &motion_error);
         if (cpi->oxcf.aq_mode == VARIANCE_AQ) {
-          vp9_clear_system_state();  // __asm emms;
-          motion_error *= error_weight;
+          vp9_clear_system_state();
+          motion_error = (int)(motion_error * error_weight);
         }
 
         // If the current best reference mv is not centered 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_mv, &tmp_mv.as_mv,
                                    &tmp_err);
           if (cpi->oxcf.aq_mode == VARIANCE_AQ) {
-            vp9_clear_system_state();  // __asm emms;
-            tmp_err *= error_weight;
+            vp9_clear_system_state();
+            tmp_err = (int)(tmp_err * error_weight);
           }
 
           if (tmp_err < motion_error) {
             motion_error = tmp_err;
             mv.as_int = tmp_mv.as_int;
           }
         }
 
-        // Experimental search in an older reference frame
+        // Search in an older reference frame.
         if (cm->current_video_frame > 1) {
-          // Simple 0,0 motion with no mv overhead
+          // Assume 0,0 motion with no mv overhead.
           int gf_motion_error;
 
           xd->plane[0].pre[0].buf = gld_yv12->y_buffer + recon_yoffset;
-          gf_motion_error = zz_motion_search(cpi, x);
+          gf_motion_error = zz_motion_search(x);
 
           first_pass_motion_search(cpi, x, &zero_mv, &tmp_mv.as_mv,
                                    &gf_motion_error);
           if (cpi->oxcf.aq_mode == VARIANCE_AQ) {
-            vp9_clear_system_state();  // __asm emms;
-            gf_motion_error *= error_weight;
+            vp9_clear_system_state();
+            gf_motion_error = (int)(gf_motion_error * error_weight);
           }
 
           if (gf_motion_error < motion_error && gf_motion_error < this_error)
-            second_ref_count++;
+            ++second_ref_count;
 
-          // Reset to last frame as reference buffer
+          // Reset to last frame as reference buffer.
           xd->plane[0].pre[0].buf = lst_yv12->y_buffer + recon_yoffset;
           xd->plane[1].pre[0].buf = lst_yv12->u_buffer + recon_uvoffset;
           xd->plane[2].pre[0].buf = 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.
+          // 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 */
+        // Start by assuming that intra mode is 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.
+          // 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++;
+            ++neutral_count;
 
           mv.as_mv.row *= 8;
           mv.as_mv.col *= 8;
           this_error = motion_error;
           vp9_set_mbmode_and_mvs(xd, NEWMV, &mv.as_mv);
           xd->mi_8x8[0]->mbmi.tx_size = TX_4X4;
           xd->mi_8x8[0]->mbmi.ref_frame[0] = LAST_FRAME;
           xd->mi_8x8[0]->mbmi.ref_frame[1] = NONE;
           vp9_build_inter_predictors_sby(xd, mb_row << 1, mb_col << 1, bsize);
-          vp9_encode_sby(x, bsize);
+          vp9_encode_sby_pass1(x, bsize);
           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++;
+          ++intercount;
 
           best_ref_mv.as_int = mv.as_int;
 
-          // Was the vector non-zero
           if (mv.as_int) {
-            mvcount++;
+            ++mvcount;
 
-            // Was it different from the last non zero vector
+            // Non-zero vector, was it different from the last non zero vector?
             if (mv.as_int != lastmv_as_int)
-              new_mv_count++;
+              ++new_mv_count;
             lastmv_as_int = mv.as_int;
 
-            // Does the Row vector point inwards or outwards
+            // Does the row vector point inwards or outwards?
             if (mb_row < cm->mb_rows / 2) {
               if (mv.as_mv.row > 0)
-                sum_in_vectors--;
+                --sum_in_vectors;
               else if (mv.as_mv.row < 0)
-                sum_in_vectors++;
+                ++sum_in_vectors;
             } else if (mb_row > cm->mb_rows / 2) {
               if (mv.as_mv.row > 0)
-                sum_in_vectors++;
+                ++sum_in_vectors;
               else if (mv.as_mv.row < 0)
-                sum_in_vectors--;
+                --sum_in_vectors;
             }
 
-            // Does the Row vector point inwards or outwards
+            // Does the col vector point inwards or outwards?
             if (mb_col < cm->mb_cols / 2) {
               if (mv.as_mv.col > 0)
-                sum_in_vectors--;
+                --sum_in_vectors;
               else if (mv.as_mv.col < 0)
-                sum_in_vectors++;
+                ++sum_in_vectors;
             } else if (mb_col > cm->mb_cols / 2) {
               if (mv.as_mv.col > 0)
-                sum_in_vectors++;
+                ++sum_in_vectors;
               else if (mv.as_mv.col < 0)
-                sum_in_vectors--;
+                --sum_in_vectors;
             }
           }
         }
       } else {
         sr_coded_error += (int64_t)this_error;
       }
       coded_error += (int64_t)this_error;
 
-      // adjust to the next column of macroblocks
+      // Adjust to the next column of MBs.
       x->plane[0].src.buf += 16;
       x->plane[1].src.buf += uv_mb_height;
       x->plane[2].src.buf += uv_mb_height;
 
       recon_yoffset += 16;
       recon_uvoffset += uv_mb_height;
     }
 
-    // adjust to the next row of mbs
+    // Adjust to the next row of MBs.
     x->plane[0].src.buf += 16 * x->plane[0].src.stride - 16 * cm->mb_cols;
     x->plane[1].src.buf += uv_mb_height * x->plane[1].src.stride -
                            uv_mb_height * cm->mb_cols;
     x->plane[2].src.buf += uv_mb_height * x->plane[1].src.stride -
                            uv_mb_height * cm->mb_cols;
 
-    vp9_clear_system_state();  // __asm emms;
+    vp9_clear_system_state();
   }
 
-  vp9_clear_system_state();  // __asm emms;
+  vp9_clear_system_state();
   {
     FIRSTPASS_STATS fps;
 
     fps.frame = cm->current_video_frame;
-    fps.intra_error = intra_error >> 8;
-    fps.coded_error = coded_error >> 8;
-    fps.sr_coded_error = sr_coded_error >> 8;
+    fps.intra_error = (double)(intra_error >> 8);
+    fps.coded_error = (double)(coded_error >> 8);
+    fps.sr_coded_error = (double)(sr_coded_error >> 8);
     fps.ssim_weighted_pred_err = fps.coded_error * simple_weight(cpi->Source);
     fps.count = 1.0;
     fps.pcnt_inter = (double)intercount / cm->MBs;
     fps.pcnt_second_ref = (double)second_ref_count / cm->MBs;
     fps.pcnt_neutral = (double)neutral_count / cm->MBs;
 
     if (mvcount > 0) {
       fps.MVr = (double)sum_mvr / mvcount;
       fps.mvr_abs = (double)sum_mvr_abs / mvcount;
       fps.MVc = (double)sum_mvc / mvcount;
@@ skipping 13 matching lines @@
       fps.mv_in_out_count = 0.0;
       fps.new_mv_count = 0.0;
       fps.pcnt_motion = 0.0;
     }
 
     // TODO(paulwilkins):  Handle the case when duration is set to 0, or
     // something less than the full time between subsequent values of
     // cpi->source_time_stamp.
     fps.duration = (double)(cpi->source->ts_end - cpi->source->ts_start);
 
-    // don't want to do output stats with a stack variable!
+    // Don't want to do output stats with a stack variable!
     twopass->this_frame_stats = fps;
-    output_stats(cpi, cpi->output_pkt_list, &twopass->this_frame_stats);
+    output_stats(&twopass->this_frame_stats, cpi->output_pkt_list);
     accumulate_stats(&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
+  // the prediction is good enough... but also don't allow it to lag too far.
   if ((twopass->sr_update_lag > 3) ||
       ((cm->current_video_frame > 0) &&
        (twopass->this_frame_stats.pcnt_inter > 0.20) &&
        ((twopass->this_frame_stats.intra_error /
          DOUBLE_DIVIDE_CHECK(twopass->this_frame_stats.coded_error)) > 2.0))) {
     vp8_yv12_copy_frame(lst_yv12, gld_yv12);
     twopass->sr_update_lag = 1;
   } else {
-    twopass->sr_update_lag++;
+    ++twopass->sr_update_lag;
   }
-  // swap frame pointers so last frame refers to the frame we just compressed
+  // Swap frame pointers so last frame refers to the frame we just compressed.
   swap_yv12(lst_yv12, new_yv12);
 
-  vp9_extend_frame_borders(lst_yv12, cm->subsampling_x, cm->subsampling_y);
+  vp9_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
+  // Use this to see what the first pass reconstruction looks like.
   if (0) {
     char filename[512];
     FILE *recon_file;
     snprintf(filename, sizeof(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++;
+  ++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.
-//
-
-
+// Estimate a cost per mb attributable to overheads such as the coding of modes
+// and motion vectors. This currently makes simplistic assumptions for testing.
 static double bitcost(double prob) {
   return -(log(prob) / log(2.0));
 }
 
-static int64_t estimate_modemvcost(VP9_COMP *cpi,
-                                     FIRSTPASS_STATS *fpstats) {
-#if 0
-  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_rc_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_rc_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(paulwilkins): Fix overhead costs for extended Q range.
-#endif
-  return 0;
-}
-
 static double calc_correction_factor(double err_per_mb,
                                      double err_divisor,
                                      double pt_low,
                                      double pt_high,
                                      int q) {
   const double error_term = err_per_mb / err_divisor;
 
   // Adjustment based on actual quantizer to power term.
   const double power_term = MIN(vp9_convert_qindex_to_q(q) * 0.0125 + pt_low,
                                 pt_high);
 
-  // Calculate correction factor
+  // Calculate correction factor.
   if (power_term < 1.0)
     assert(error_term >= 0.0);
 
   return fclamp(pow(error_term, power_term), 0.05, 5.0);
 }
 
 int vp9_twopass_worst_quality(VP9_COMP *cpi, FIRSTPASS_STATS *fpstats,
                               int section_target_bandwitdh) {
   int q;
   const int num_mbs = cpi->common.MBs;
   int target_norm_bits_per_mb;
   const RATE_CONTROL *const rc = &cpi->rc;
 
   const double section_err = fpstats->coded_error / fpstats->count;
   const double err_per_mb = section_err / num_mbs;
 
   if (section_target_bandwitdh <= 0)
     return rc->worst_quality;          // 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);
 
   // Try and pick a max Q that will be high enough to encode the
   // content at the given rate.
-  for (q = rc->best_quality; q < rc->worst_quality; q++) {
+  for (q = rc->best_quality; q < rc->worst_quality; ++q) {
     const double err_correction_factor = calc_correction_factor(err_per_mb,
                                              ERR_DIVISOR, 0.5, 0.90, q);
     const int bits_per_mb_at_this_q = vp9_rc_bits_per_mb(INTER_FRAME, q,
                                                          err_correction_factor);
     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)
@@ skipping 12 matching lines @@
 
   zero_stats(&twopass->total_stats);
   zero_stats(&twopass->total_left_stats);
 
   if (!twopass->stats_in_end)
     return;
 
   twopass->total_stats = *twopass->stats_in_end;
   twopass->total_left_stats = 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.
+  // 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.
+  // It is calculated based on the actual durations of all frames from the
+  // first pass.
   vp9_new_framerate(cpi, 10000000.0 * twopass->total_stats.count /
                         twopass->total_stats.duration);
 
   cpi->output_framerate = oxcf->framerate;
   twopass->bits_left = (int64_t)(twopass->total_stats.duration *
                                  oxcf->target_bandwidth / 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
+  // are still boosted appropriately for KF/GF/ARF.
   twopass->kf_intra_err_min = KF_MB_INTRA_MIN * cpi->common.MBs;
   twopass->gf_intra_err_min = GF_MB_INTRA_MIN * cpi->common.MBs;
 
-  // This variable monitors how far behind the second ref update is lagging
+  // This variable monitors how far behind the second ref update is lagging.
   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;
-    start_pos = twopass->stats_in;  // Note the starting "file" position.
+    start_pos = twopass->stats_in;
 
     while (input_stats(twopass, &this_frame) != EOF) {
       const double iiratio = this_frame.intra_error /
                                  DOUBLE_DIVIDE_CHECK(this_frame.coded_error);
       sum_iiratio += fclamp(iiratio, 1.0, 20.0);
     }
 
     twopass->avg_iiratio = sum_iiratio /
         DOUBLE_DIVIDE_CHECK((double)twopass->total_stats.count);
 
-    // Reset file position
     reset_fpf_position(twopass, start_pos);
   }
 
   // Scan the first pass file and calculate a modified total error based upon
   // the bias/power function used to allocate bits.
   {
     double av_error = twopass->total_stats.ssim_weighted_pred_err /
                       DOUBLE_DIVIDE_CHECK(twopass->total_stats.count);
 
-    start_pos = twopass->stats_in;  // Note starting "file" position
+    start_pos = twopass->stats_in;
 
     twopass->modified_error_total = 0.0;
     twopass->modified_error_min =
       (av_error * oxcf->two_pass_vbrmin_section) / 100;
     twopass->modified_error_max =
       (av_error * oxcf->two_pass_vbrmax_section) / 100;
 
     while (input_stats(twopass, &this_frame) != EOF) {
       twopass->modified_error_total +=
           calculate_modified_err(cpi, &this_frame);
     }
     twopass->modified_error_left = twopass->modified_error_total;
 
     reset_fpf_position(twopass, start_pos);
   }
 }
 
-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.
+// This function gives an estimate of how badly we believe the prediction
+// quality is decaying from frame to frame.
 static double get_prediction_decay_rate(const VP9_COMMON *cm,
                                         const FIRSTPASS_STATS *next_frame) {
   // Look at the observed drop in prediction quality between the last frame
   // and the GF buffer (which contains an older frame).
   const double mb_sr_err_diff = (next_frame->sr_coded_error -
                                      next_frame->coded_error) / cm->MBs;
   const double second_ref_decay = mb_sr_err_diff <= 512.0
       ? fclamp(pow(1.0 - (mb_sr_err_diff / 512.0), 0.5), 0.85, 1.0)
       : 0.85;
 
@@ skipping 12 matching lines @@
   // 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;
 
-    // Look ahead a few frames to see if static condition
-    // persists...
-    for (j = 0; j < still_interval; j++) {
+    // Look ahead a few frames to see if static condition persists...
+    for (j = 0; j < still_interval; ++j) {
       if (EOF == input_stats(&cpi->twopass, &tmp_next_frame))
         break;
 
       if (tmp_next_frame.pcnt_inter - tmp_next_frame.pcnt_motion < 0.999)
         break;
     }
 
     reset_fpf_position(&cpi->twopass, position);
 
-    // Only if it does do we signal a transition to still
+    // Only if it does do we signal a transition to still.
     if (j == still_interval)
       trans_to_still = 1;
   }
 
   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
+// reflect this.
 static int detect_flash(const struct twopass_rc *twopass, int offset) {
   FIRSTPASS_STATS next_frame;
 
   int flash_detected = 0;
 
   // Read the frame data.
   // The return is FALSE (no flash detected) if not a valid frame
   if (read_frame_stats(twopass, &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.
+    // compared to pcnt_inter.
     if (next_frame.pcnt_second_ref > next_frame.pcnt_inter &&
         next_frame.pcnt_second_ref >= 0.5)
       flash_detected = 1;
   }
 
   return flash_detected;
 }
 
-// Update the motion related elements to the GF arf boost calculation
+// Update the motion related elements to the GF arf boost calculation.
 static void accumulate_frame_motion_stats(
   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 motion_pct;
 
   // Accumulate motion stats.
   motion_pct = this_frame->pcnt_motion;
 
-  // Accumulate Motion In/Out of frame stats
+  // 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)
+  // the motion field is (a ratio of absmv / mv).
   if (motion_pct > 0.05) {
     const double this_frame_mvr_ratio = fabs(this_frame->mvr_abs) /
                            DOUBLE_DIVIDE_CHECK(fabs(this_frame->MVr));
 
     const double 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
+  // 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
+  // Increase boost for frames where new data coming into frame (e.g. 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
+  // In the extreme case the boost is halved.
   else
     frame_boost += frame_boost * (this_frame_mv_in_out / 2.0);
 
   return MIN(frame_boost, GF_RMAX);
 }
 
 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;
   struct twopass_rc *const twopass = &cpi->twopass;
   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;
   int flash_detected = 0;
 
-  // Search forward from the proposed arf/next gf position
-  for (i = 0; i < f_frames; i++) {
+  // Search forward from the proposed arf/next gf position.
+  for (i = 0; i < f_frames; ++i) {
     if (read_frame_stats(twopass, &this_frame, (i + offset)) == EOF)
       break;
 
-    // Update the motion related elements to the boost calculation
+    // Update the motion related elements to the boost calculation.
     accumulate_frame_motion_stats(&this_frame,
                                   &this_frame_mv_in_out, &mv_in_out_accumulator,
                                   &abs_mv_in_out_accumulator,
                                   &mv_ratio_accumulator);
 
     // We want to discount the flash frame itself and the recovery
     // frame that follows as both will have poor scores.
     flash_detected = detect_flash(twopass, i + offset) ||
                      detect_flash(twopass, i + offset + 1);
 
-    // Cumulative effect of prediction quality decay
+    // Accumulate the effect of prediction quality decay.
     if (!flash_detected) {
       decay_accumulator *= get_prediction_decay_rate(&cpi->common, &this_frame);
       decay_accumulator = decay_accumulator < MIN_DECAY_FACTOR
                           ? MIN_DECAY_FACTOR : 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
+  // 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--) {
+  // Search backward towards last gf position.
+  for (i = -1; i >= -b_frames; --i) {
     if (read_frame_stats(twopass, &this_frame, (i + offset)) == EOF)
       break;
 
-    // Update the motion related elements to the boost calculation
+    // Update the motion related elements to the boost calculation.
     accumulate_frame_motion_stats(&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(twopass, i + offset) ||
                      detect_flash(twopass, i + offset + 1);
 
-    // Cumulative effect of prediction quality decay
+    // Cumulative effect of prediction quality decay.
     if (!flash_detected) {
       decay_accumulator *= get_prediction_decay_rate(&cpi->common, &this_frame);
       decay_accumulator = decay_accumulator < MIN_DECAY_FACTOR
                               ? MIN_DECAY_FACTOR : decay_accumulator;
     }
 
     boost_score += (decay_accumulator *
                     calc_frame_boost(cpi, &this_frame, this_frame_mv_in_out));
   }
   *b_boost = (int)boost_score;
@@ skipping 29 matching lines @@
     for (i = start; i <= end; ++i) {
       cfo[idx] = i;
       cpi->arf_buffer_idx[idx] = arf_idx;
       cpi->arf_weight[idx] = -1;
       ++idx;
     }
     cpi->new_frame_coding_order_period = idx;
     return;
   }
 
-  // ARF Group: work out the ARF schedule.
-  // Mark ARF frames as negative.
+  // ARF Group: Work out the ARF schedule and mark ARF frames as negative.
   if (end < 0) {
     // printf("start:%d end:%d\n", -end, -end);
     // ARF frame is at the end of the range.
     cfo[idx] = end;
     // What ARF buffer does this ARF use as predictor.
     cpi->arf_buffer_idx[idx] = (arf_idx > 2) ? (arf_idx - 1) : 2;
     cpi->arf_weight[idx] = level;
     ++idx;
     abs_end = -end;
   } else {
@@ skipping 102 matching lines @@
   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 loop_decay_rate = 1.00;
   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;
   double mv_ratio_accumulator_thresh;
-  const int max_bits = frame_max_bits(cpi);     // Max for a single frame
+  const int max_bits = frame_max_bits(cpi);  // Max bits 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;
   int flash_detected;
   int active_max_gf_interval;
   RATE_CONTROL *const rc = &cpi->rc;
 
   twopass->gf_group_bits = 0;
 
-  vp9_clear_system_state();  // __asm emms;
+  vp9_clear_system_state();
 
   start_pos = twopass->stats_in;
 
   // 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
+  // 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;
 
   // If this is a key frame or the overlay from a previous arf then
-  // The error score / cost of this frame has already been accounted for.
+  // the error score / cost of this frame has already been accounted for.
   if (cpi->common.frame_type == KEY_FRAME || rc->source_alt_ref_active)
     gf_group_err -= gf_first_frame_err;
 
   // Motion breakout threshold for loop below depends on image size.
   mv_ratio_accumulator_thresh = (cpi->common.width + cpi->common.height) / 10.0;
 
   // Work out a maximum interval for the GF.
   // If the image appears completely static we can extend beyond this.
   // The value chosen depends on the active Q range. At low Q we have
   // bits to spare and are better with a smaller interval and smaller boost.
   // At high Q when there are few bits to spare we are better with a longer
   // interval to spread the cost of the GF.
   //
   active_max_gf_interval =
     12 + ((int)vp9_convert_qindex_to_q(rc->last_q[INTER_FRAME]) >> 5);
 
   if (active_max_gf_interval > rc->max_gf_interval)
     active_max_gf_interval = rc->max_gf_interval;
 
   i = 0;
   while (i < twopass->static_scene_max_gf_interval && i < rc->frames_to_key) {
-    i++;    // Increment the loop counter
+    ++i;
 
-    // Accumulate error score of frames in this gf group
+    // 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(twopass, &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(twopass, 0);
 
-    // Update the motion related elements to the boost calculation
+    // Update the motion related elements to the boost calculation.
     accumulate_frame_motion_stats(&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
+    // Accumulate the effect of prediction quality decay.
     if (!flash_detected) {
       last_loop_decay_rate = loop_decay_rate;
       loop_decay_rate = get_prediction_decay_rate(&cpi->common, &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 static image after a fade or other transition).
+      // Break clause to detect very still sections after motion. For example,
+      // a static 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 = 0;
         break;
       }
     }
 
-    // Calculate a boost number for this frame
+    // 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
+      // Break at cpi->max_gf_interval unless almost totally static.
       (i >= active_max_gf_interval && (zero_motion_accumulator < 0.995)) ||
       (
-        // Don't break out with a very short interval
+        // Don't break out with a very short interval.
         (i > MIN_GF_INTERVAL) &&
         ((boost_score > 125.0) || (next_frame.pcnt_inter < 0.75)) &&
         (!flash_detected) &&
         ((mv_ratio_accumulator > mv_ratio_accumulator_thresh) ||
          (abs_mv_in_out_accumulator > 3.0) ||
          (mv_in_out_accumulator < -2.0) ||
          ((boost_score - old_boost_score) < IIFACTOR)))) {
       boost_score = old_boost_score;
       break;
     }
 
     *this_frame = next_frame;
 
     old_boost_score = boost_score;
   }
 
   twopass->gf_zeromotion_pct = (int)(zero_motion_accumulator * 1000.0);
 
-  // Don't allow a gf too near the next kf
+  // Don't allow a gf too near the next kf.
   if ((rc->frames_to_key - i) < MIN_GF_INTERVAL) {
     while (i < (rc->frames_to_key + !rc->next_key_frame_forced)) {
-      i++;
+      ++i;
 
       if (EOF == input_stats(twopass, this_frame))
         break;
 
       if (i < rc->frames_to_key) {
         mod_frame_err = calculate_modified_err(cpi, this_frame);
         gf_group_err += mod_frame_err;
       }
     }
   }
 
 #if CONFIG_MULTIPLE_ARF
   if (cpi->multi_arf_enabled) {
     // Initialize frame coding order variables.
     cpi->new_frame_coding_order_period = 0;
     cpi->next_frame_in_order = 0;
     cpi->arf_buffered = 0;
     vp9_zero(cpi->frame_coding_order);
     vp9_zero(cpi->arf_buffer_idx);
     vpx_memset(cpi->arf_weight, -1, sizeof(cpi->arf_weight));
   }
 #endif
 
   // Set the interval until the next gf.
   if (cpi->common.frame_type == KEY_FRAME || rc->source_alt_ref_active)
     rc->baseline_gf_interval = i - 1;
   else
     rc->baseline_gf_interval = i;
 
-  // Should we use the alternate reference frame
+  // Should we use the alternate reference frame.
   if (allow_alt_ref &&
       (i < cpi->oxcf.lag_in_frames) &&
       (i >= MIN_GF_INTERVAL) &&
-      // for real scene cuts (not forced kfs) dont allow arf very near kf.
+      // For real scene cuts (not forced kfs) don't allow arf very near kf.
       (rc->next_key_frame_forced ||
       (i <= (rc->frames_to_key - MIN_GF_INTERVAL)))) {
-    // Alternative boost calculation for alt ref
+    // Calculate the boost for alt ref.
     rc->gfu_boost = calc_arf_boost(cpi, 0, (i - 1), (i - 1), &f_boost,
                                    &b_boost);
     rc->source_alt_ref_pending = 1;
 
 #if CONFIG_MULTIPLE_ARF
     // Set the ARF schedule.
     if (cpi->multi_arf_enabled) {
       schedule_frames(cpi, 0, -(rc->baseline_gf_interval - 1), 2, 1, 0);
     }
 #endif
@@ skipping 41 matching lines @@
     printf("\n");
     printf("Weight:   ");
     for (i = 0; i < cpi->new_frame_coding_order_period; ++i) {
       printf("%4d ", cpi->arf_weight[i]);
     }
     printf("\n");
   }
 #endif
 #endif
 
-  // Calculate the bits to be allocated to the group as a whole
+  // Calculate the bits to be allocated to the group as a whole.
   if (twopass->kf_group_bits > 0 && twopass->kf_group_error_left > 0) {
     twopass->gf_group_bits = (int64_t)(cpi->twopass.kf_group_bits *
                 (gf_group_err / cpi->twopass.kf_group_error_left));
   } else {
     twopass->gf_group_bits = 0;
   }
   twopass->gf_group_bits = (twopass->gf_group_bits < 0) ?
      0 : (twopass->gf_group_bits > twopass->kf_group_bits) ?
      twopass->kf_group_bits : twopass->gf_group_bits;
 
   // Clip cpi->twopass.gf_group_bits based on user supplied data rate
-  // variability limit (cpi->oxcf.two_pass_vbrmax_section)
+  // variability limit, cpi->oxcf.two_pass_vbrmax_section.
   if (twopass->gf_group_bits > (int64_t)max_bits * rc->baseline_gf_interval)
     twopass->gf_group_bits = (int64_t)max_bits * rc->baseline_gf_interval;
 
-  // Reset the file position
+  // Reset the file position.
   reset_fpf_position(twopass, start_pos);
 
   // Assign  bits to the arf or gf.
   for (i = 0; i <= (rc->source_alt_ref_pending &&
                     cpi->common.frame_type != KEY_FRAME); ++i) {
     int allocation_chunks;
     int q = rc->last_q[INTER_FRAME];
     int gf_bits;
 
     int boost = (rc->gfu_boost * gfboost_qadjust(q)) / 100;
 
-    // Set max and minimum boost and hence minimum allocation
+    // Set max and minimum boost and hence minimum allocation.
     boost = clamp(boost, 125, (rc->baseline_gf_interval + 1) * 200);
 
     if (rc->source_alt_ref_pending && i == 0)
       allocation_chunks = ((rc->baseline_gf_interval + 1) * 100) + boost;
     else
       allocation_chunks = (rc->baseline_gf_interval * 100) + (boost - 100);
 
-    // Prevent overflow
+    // Prevent overflow.
     if (boost > 1023) {
       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
+    // the boost number.
     gf_bits = (int)((double)boost * (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
+    // based on the error score of the frame itself.
     if (rc->baseline_gf_interval < 1 ||
         mod_frame_err < gf_group_err / (double)rc->baseline_gf_interval) {
       double alt_gf_grp_bits = (double)twopass->kf_group_bits  *
         (mod_frame_err * (double)rc->baseline_gf_interval) /
         DOUBLE_DIVIDE_CHECK(twopass->kf_group_error_left);
 
       int 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.
       int alt_gf_bits = (int)((double)twopass->kf_group_bits *
                         mod_frame_err /
                         DOUBLE_DIVIDE_CHECK(twopass->kf_group_error_left));
 
       if (alt_gf_bits > gf_bits)
         gf_bits = alt_gf_bits;
     }
 
-    // Dont allow a negative value for gf_bits
+    // Don't allow a negative value for gf_bits.
     if (gf_bits < 0)
       gf_bits = 0;
 
     if (i == 0) {
       twopass->gf_bits = gf_bits;
     }
     if (i == 1 ||
         (!rc->source_alt_ref_pending &&
          cpi->common.frame_type != KEY_FRAME)) {
-      // Per frame bit target for this frame
+      // Calculate the per frame bit target for this frame.
       vp9_rc_set_frame_target(cpi, gf_bits);
     }
   }
 
   {
-    // Adjust KF group bits and error remaining
+    // Adjust KF group bits and error remaining.
     twopass->kf_group_error_left -= (int64_t)gf_group_err;
     twopass->kf_group_bits -= twopass->gf_group_bits;
 
     if (twopass->kf_group_bits < 0)
       twopass->kf_group_bits = 0;
 
-    // If this is an arf update we want to remove the score for the
-    // overlay frame at the end which will usually be very cheap to code.
-    // The overlay frame has already in effect been coded so we want to spread
-    // the remaining bits amoung the other frames/
+    // If this is an arf update we want to remove the score for the overlay
+    // frame at the end which will usually be very cheap to code.
+    // The overlay frame has already, in effect, been coded so we want to spread
+    // the remaining bits among the other frames.
     // For normal GFs remove the score for the GF itself unless this is
     // also a key frame in which case it has already been accounted for.
     if (rc->source_alt_ref_pending) {
-      twopass->gf_group_error_left = (int64_t)gf_group_err - mod_frame_err;
+      twopass->gf_group_error_left = (int64_t)(gf_group_err - mod_frame_err);
     } else if (cpi->common.frame_type != KEY_FRAME) {
       twopass->gf_group_error_left = (int64_t)(gf_group_err
                                                    - gf_first_frame_err);
     } else {
       twopass->gf_group_error_left = (int64_t)gf_group_err;
     }
 
     twopass->gf_group_bits -= twopass->gf_bits;
 
     if (twopass->gf_group_bits < 0)
       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 divide by 0 in the
+    // despite MIN_GF_INTERVAL and would cause a divide by 0 in the
     // calculation of alt_extra_bits.
     if (rc->baseline_gf_interval >= 3) {
       const int boost = rc->source_alt_ref_pending ? b_boost : rc->gfu_boost;
 
       if (boost >= 150) {
         const int pct_extra = MIN(20, (boost - 100) / 50);
         const int alt_extra_bits = (int)((twopass->gf_group_bits * pct_extra) /
                                        100);
         twopass->gf_group_bits -= alt_extra_bits;
       }
     }
   }
 
   if (cpi->common.frame_type != KEY_FRAME) {
     FIRSTPASS_STATS sectionstats;
 
     zero_stats(&sectionstats);
     reset_fpf_position(twopass, start_pos);
 
-    for (i = 0; i < rc->baseline_gf_interval; i++) {
+    for (i = 0; i < rc->baseline_gf_interval; ++i) {
       input_stats(twopass, &next_frame);
       accumulate_stats(&sectionstats, &next_frame);
     }
 
     avg_stats(&sectionstats);
 
     twopass->section_intra_rating = (int)
       (sectionstats.intra_error /
       DOUBLE_DIVIDE_CHECK(sectionstats.coded_error));
 
@@ skipping 35 matching lines @@
   // Per frame bit target for this frame.
   vp9_rc_set_frame_target(cpi, target_frame_size);
 }
 
 static int test_candidate_kf(VP9_COMP *cpi,
                              const FIRSTPASS_STATS *last_frame,
                              const FIRSTPASS_STATS *this_frame,
                              const FIRSTPASS_STATS *next_frame) {
   int is_viable_kf = 0;
 
-  // Does the frame satisfy the primary criteria of a key frame
-  //      If so, then examine how well it predicts subsequent frames
+  // 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->pcnt_inter - this_frame->pcnt_neutral) < 0.35) &&
         ((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) ||
+              DOUBLE_DIVIDE_CHECK(this_frame->coded_error) > 0.40) ||
          (fabs(last_frame->intra_error - this_frame->intra_error) /
-              DOUBLE_DIVIDE_CHECK(this_frame->intra_error) >
-          .40) ||
+              DOUBLE_DIVIDE_CHECK(this_frame->intra_error) > 0.40) ||
          ((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;
 
     local_next_frame = *next_frame;
 
-    // Note the starting file position so we can reset to it
+    // 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++) {
+    // Examine how well the key frame predicts subsequent frames.
+    for (i = 0; i < 16; ++i) {
       double 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
+      // Cumulative effect of decay in prediction quality.
       if (local_next_frame.pcnt_inter > 0.85)
         decay_accumulator *= local_next_frame.pcnt_inter;
       else
         decay_accumulator *= (0.85 + local_next_frame.pcnt_inter) / 2.0;
 
-      // decay_accumulator = decay_accumulator * local_next_frame.pcnt_inter;
-
-      // Keep a running total
+      // Keep a running total.
       boost_score += (decay_accumulator * next_iiratio);
 
-      // Test various breakout clauses
+      // 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)
-         ) {
+          (local_next_frame.intra_error < 200)) {
         break;
       }
 
       old_boost_score = boost_score;
 
       // Get the next frame details
       if (EOF == input_stats(&cpi->twopass, &local_next_frame))
         break;
     }
 
@@ skipping 26 matching lines @@
 
   double kf_mod_err = 0.0;
   double kf_group_err = 0.0;
   double recent_loop_decay[8] = {1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0};
 
   RATE_CONTROL *const rc = &cpi->rc;
   struct twopass_rc *const twopass = &cpi->twopass;
 
   vp9_zero(next_frame);
 
-  vp9_clear_system_state();  // __asm emms;
+  vp9_clear_system_state();
 
   start_position = twopass->stats_in;
   cpi->common.frame_type = KEY_FRAME;
 
-  // is this a forced key frame by interval
+  // Is this a forced key frame by interval.
   rc->this_key_frame_forced = rc->next_key_frame_forced;
 
-  // Clear the alt ref active flag as this can never be active on a key frame
+  // Clear the alt ref active flag as this can never be active on a key frame.
   rc->source_alt_ref_active = 0;
 
-  // Kf is always a gf so clear frames till next gf counter
+  // KF is always a GF so clear frames till next gf counter.
   rc->frames_till_gf_update_due = 0;
 
   rc->frames_to_key = 1;
 
-  // Take a copy of the initial frame details
+  // Take a copy of the initial frame details.
   first_frame = *this_frame;
 
   twopass->kf_group_bits = 0;        // Total bits available to kf group
   twopass->kf_group_error_left = 0;  // Group modified error score.
 
   kf_mod_err = calculate_modified_err(cpi, this_frame);
 
-  // find the next keyframe
+  // Find the next keyframe.
   i = 0;
   while (twopass->stats_in < twopass->stats_in_end) {
-    // Accumulate kf group error
+    // Accumulate kf group error.
     kf_group_err += calculate_modified_err(cpi, this_frame);
 
-    // load a the next frame's stats
+    // Load the next frame's stats.
     last_frame = *this_frame;
     input_stats(twopass, this_frame);
 
     // Provided that we are not at the end of the file...
     if (cpi->oxcf.auto_key &&
         lookup_next_frame_stats(twopass, &next_frame) != EOF) {
-      // Normal scene cut check
+      // Check for a scene cut.
       if (test_candidate_kf(cpi, &last_frame, this_frame, &next_frame))
         break;
 
-
-      // How fast is prediction quality decaying
+      // How fast is the prediction quality decaying?
       loop_decay_rate = get_prediction_decay_rate(&cpi->common, &next_frame);
 
       // We want to know something about the recent past... rather than
-      // as used elsewhere where we are concened with decay in prediction
+      // as used elsewhere where we are concerned 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++)
+      for (j = 0; j < 8; ++j)
         decay_accumulator *= recent_loop_decay[j];
 
       // Special check for transition or high motion followed by a
-      // to a static scene.
+      // 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
-      rc->frames_to_key++;
+      // Step on to the next frame.
+      ++rc->frames_to_key;
 
       // If we don't have a real key frame within the next two
-      // forcekeyframeevery intervals then break out of the loop.
+      // key_frame_frequency intervals then break out of the loop.
       if (rc->frames_to_key >= 2 * (int)cpi->key_frame_frequency)
         break;
     } else {
-      rc->frames_to_key++;
+      ++rc->frames_to_key;
     }
-    i++;
+    ++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
+  // This code centers the extra kf if the actual natural interval
+  // is between 1x and 2x.
   if (cpi->oxcf.auto_key &&
       rc->frames_to_key > (int)cpi->key_frame_frequency) {
     FIRSTPASS_STATS tmp_frame;
 
     rc->frames_to_key /= 2;
 
-    // Copy first frame details
+    // Copy first frame details.
     tmp_frame = first_frame;
 
-    // Reset to the start of the group
+    // Reset to the start of the group.
     reset_fpf_position(twopass, start_position);
 
     kf_group_err = 0;
 
-    // Rescan to get the correct error data for the forced kf group
-    for (i = 0; i < rc->frames_to_key; i++) {
-      // Accumulate kf group errors
+    // Rescan to get the correct error data for the forced kf group.
+    for (i = 0; i < rc->frames_to_key; ++i) {
+      // Accumulate kf group errors.
       kf_group_err += calculate_modified_err(cpi, &tmp_frame);
 
       // Load the next frame's stats.
       input_stats(twopass, &tmp_frame);
     }
     rc->next_key_frame_forced = 1;
   } else if (twopass->stats_in == twopass->stats_in_end) {
     rc->next_key_frame_forced = 1;
   } else {
     rc->next_key_frame_forced = 0;
   }
 
-  // Special case for the last key frame of the file
+  // Special case for the last key frame of the file.
   if (twopass->stats_in >= twopass->stats_in_end) {
-    // Accumulate kf group error
+    // Accumulate kf group error.
     kf_group_err += calculate_modified_err(cpi, this_frame);
   }
 
   // Calculate the number of bits that should be assigned to the kf group.
   if (twopass->bits_left > 0 && twopass->modified_error_left > 0.0) {
-    // Max for a single normal frame (not key frame)
+    // Maximum number of bits for a single normal frame (not key frame).
     int max_bits = frame_max_bits(cpi);
 
-    // Maximum bits for the kf group
+    // Maximum number of bits allocated to the key frame group.
     int64_t max_grp_bits;
 
     // Default allocation based on bits left and relative
-    // complexity of the section
+    // complexity of the section.
     twopass->kf_group_bits = (int64_t)(twopass->bits_left *
        (kf_group_err / twopass->modified_error_left));
 
     // Clip based on maximum per frame rate defined by the user.
     max_grp_bits = (int64_t)max_bits * (int64_t)rc->frames_to_key;
     if (twopass->kf_group_bits > max_grp_bits)
       twopass->kf_group_bits = max_grp_bits;
   } else {
     twopass->kf_group_bits = 0;
   }
-  // Reset the first pass file position
+  // Reset the first pass file position.
   reset_fpf_position(twopass, 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;
 
   // Scan through the kf group collating various stats.
-  for (i = 0; i < rc->frames_to_key; i++) {
+  for (i = 0; i < rc->frames_to_key; ++i) {
     double r;
 
     if (EOF == input_stats(twopass, &next_frame))
       break;
 
     // 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);
     }
 
     // For the first few frames collect data to decide kf boost.
     if (i <= (rc->max_gf_interval * 2)) {
       if (next_frame.intra_error > twopass->kf_intra_err_min)
         r = (IIKFACTOR2 * next_frame.intra_error /
              DOUBLE_DIVIDE_CHECK(next_frame.coded_error));
       else
         r = (IIKFACTOR2 * twopass->kf_intra_err_min /
              DOUBLE_DIVIDE_CHECK(next_frame.coded_error));
 
       if (r > RMAX)
         r = RMAX;
 
-      // How fast is prediction quality decaying
+      // How fast is prediction quality decaying.
       if (!detect_flash(twopass, 0)) {
         loop_decay_rate = get_prediction_decay_rate(&cpi->common, &next_frame);
         decay_accumulator *= loop_decay_rate;
         decay_accumulator = decay_accumulator < MIN_DECAY_FACTOR
                               ? MIN_DECAY_FACTOR : decay_accumulator;
       }
 
       boost_score += (decay_accumulator * r);
     }
   }
 
   {
     FIRSTPASS_STATS sectionstats;
 
     zero_stats(&sectionstats);
     reset_fpf_position(twopass, start_position);
 
-    for (i = 0; i < rc->frames_to_key; i++) {
+    for (i = 0; i < rc->frames_to_key; ++i) {
       input_stats(twopass, &next_frame);
       accumulate_stats(&sectionstats, &next_frame);
     }
 
     avg_stats(&sectionstats);
 
     twopass->section_intra_rating = (int) (sectionstats.intra_error /
         DOUBLE_DIVIDE_CHECK(sectionstats.coded_error));
   }
 
-  // Reset the first pass file position
+  // Reset the first pass file position.
   reset_fpf_position(twopass, start_position);
 
-  // Work out how many bits to allocate for the key frame itself
+  // 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 < (rc->frames_to_key * 3))
       kf_boost = (rc->frames_to_key * 3);
 
     if (kf_boost < MIN_KF_BOOST)
       kf_boost = MIN_KF_BOOST;
 
     // Make a note of baseline boost and the zero motion
     // accumulator value for use elsewhere.
     rc->kf_boost = kf_boost;
     twopass->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 (optionally) 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->rc.frames_to_key-1 because key frame itself is taken
-    // care of by kf_boost.
+    // Key frame size depends on:
+    // (1) the error score for the whole key frame group,
+    // (2) the key frames' own error if this is smaller than the
+    //     average for the group (optional),
+    // (3) insuring 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 totally static we want to spend almost
+    // all of the bits on the key frame.
+    //
+    // We use (cpi->rc.frames_to_key - 1) below because the key frame itself is
+    // taken care of by kf_boost.
     if (zero_motion_accumulator >= 0.99) {
       allocation_chunks = ((rc->frames_to_key - 1) * 10) + kf_boost;
     } else {
       allocation_chunks = ((rc->frames_to_key - 1) * 100) + kf_boost;
     }
 
-    // Prevent overflow
+    // Prevent overflow.
     if (kf_boost > 1028) {
       int divisor = kf_boost >> 10;
       kf_boost /= divisor;
       allocation_chunks /= divisor;
     }
 
     twopass->kf_group_bits = (twopass->kf_group_bits < 0) ? 0
            : twopass->kf_group_bits;
 
-    // Calculate the number of bits to be spent on the key frame
+    // Calculate the number of bits to be spent on the key frame.
     twopass->kf_bits = (int)((double)kf_boost *
         ((double)twopass->kf_group_bits / allocation_chunks));
 
     // If the key frame is actually easier than the average for the
     // kf group (which does sometimes happen, e.g. 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 / rc->frames_to_key) {
       double  alt_kf_grp_bits = ((double)twopass->bits_left *
          (kf_mod_err * (double)rc->frames_to_key) /
          DOUBLE_DIVIDE_CHECK(twopass->modified_error_left));
 
       alt_kf_bits = (int)((double)kf_boost *
                           (alt_kf_grp_bits / (double)allocation_chunks));
 
       if (twopass->kf_bits > alt_kf_bits)
         twopass->kf_bits = alt_kf_bits;
     } else {
-    // 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 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.
       alt_kf_bits = (int)((double)twopass->bits_left * (kf_mod_err /
                DOUBLE_DIVIDE_CHECK(twopass->modified_error_left)));
 
       if (alt_kf_bits > twopass->kf_bits) {
         twopass->kf_bits = alt_kf_bits;
       }
     }
     twopass->kf_group_bits -= twopass->kf_bits;
     // Per frame bit target for this frame.
     vp9_rc_set_frame_target(cpi, twopass->kf_bits);
   }
 
-  // Note the total error score of the kf group minus the key frame itself
+  // Note the total error score of the kf group minus the key frame itself.
   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.
   twopass->modified_error_left -= kf_group_err;
 }
 
 void vp9_rc_get_first_pass_params(VP9_COMP *cpi) {
   VP9_COMMON *const cm = &cpi->common;
   if (!cpi->refresh_alt_ref_frame &&
       (cm->current_video_frame == 0 ||
        cm->frame_flags & FRAMEFLAGS_KEY)) {
     cm->frame_type = KEY_FRAME;
   } else {
     cm->frame_type = INTER_FRAME;
   }
-  // Do not use periodic key frames
+  // Do not use periodic key frames.
   cpi->rc.frames_to_key = INT_MAX;
 }
 
 void vp9_rc_get_second_pass_params(VP9_COMP *cpi) {
   VP9_COMMON *const cm = &cpi->common;
   RATE_CONTROL *const rc = &cpi->rc;
   struct twopass_rc *const twopass = &cpi->twopass;
   const int frames_left = (int)(twopass->total_stats.count -
                               cm->current_video_frame);
   FIRSTPASS_STATS this_frame;
@@ skipping 18 matching lines @@
     twopass->active_worst_quality = cpi->oxcf.cq_level;
   } else if (cm->current_video_frame == 0) {
     // Special case code for first frame.
     const int section_target_bandwidth = (int)(twopass->bits_left /
                                                frames_left);
     const int tmp_q = vp9_twopass_worst_quality(cpi, &twopass->total_left_stats,
                                                 section_target_bandwidth);
     twopass->active_worst_quality = tmp_q;
     rc->ni_av_qi = tmp_q;
     rc->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);
   }
   vp9_zero(this_frame);
   if (EOF == input_stats(twopass, &this_frame))
     return;
 
   this_frame_intra_error = this_frame.intra_error;
   this_frame_coded_error = this_frame.coded_error;
 
-  // keyframe and section processing !
+  // Keyframe and section processing.
   if (rc->frames_to_key == 0 ||
       (cm->frame_flags & FRAMEFLAGS_KEY)) {
-    // Define next KF group and assign bits to it
+    // Define next KF group and assign bits to it.
     this_frame_copy = this_frame;
     find_next_key_frame(cpi, &this_frame_copy);
   } else {
     cm->frame_type = INTER_FRAME;
   }
 
-  // Is this a GF / ARF (Note that a KF is always also a GF)
+  // Is this frame a GF / ARF? (Note: a key frame is always also a GF).
   if (rc->frames_till_gf_update_due == 0) {
-    // Define next gf group and assign bits to it
+    // Define next gf group and assign bits to it.
     this_frame_copy = this_frame;
 
 #if CONFIG_MULTIPLE_ARF
     if (cpi->multi_arf_enabled) {
       define_fixed_arf_period(cpi);
     } else {
 #endif
       define_gf_group(cpi, &this_frame_copy);
 #if CONFIG_MULTIPLE_ARF
     }
 #endif
 
     if (twopass->gf_zeromotion_pct > 995) {
       // As long as max_thresh for encode breakout is small enough, it is ok
-      // to enable it for show frame, i.e. set allow_encode_breakout to 2.
+      // to enable it for show frame, i.e. set allow_encode_breakout to
+      // ENCODE_BREAKOUT_LIMITED.
       if (!cm->show_frame)
         cpi->allow_encode_breakout = ENCODE_BREAKOUT_DISABLED;
       else
         cpi->allow_encode_breakout = ENCODE_BREAKOUT_LIMITED;
     }
 
     rc->frames_till_gf_update_due = rc->baseline_gf_interval;
     cpi->refresh_golden_frame = 1;
   } else {
-    // Otherwise this is an ordinary frame
-    // Assign bits from those allocated to the GF group
+    // Otherwise this is an ordinary frame.
+    // Assign bits from those allocated to the GF group.
     this_frame_copy =  this_frame;
     assign_std_frame_bits(cpi, &this_frame_copy);
   }
 
   // Keep a globally available copy of this and the next frame's iiratio.
   twopass->this_iiratio = (int)(this_frame_intra_error /
                               DOUBLE_DIVIDE_CHECK(this_frame_coded_error));
   {
     FIRSTPASS_STATS next_frame;
     if (lookup_next_frame_stats(twopass, &next_frame) != EOF) {
       twopass->next_iiratio = (int)(next_frame.intra_error /
                                  DOUBLE_DIVIDE_CHECK(next_frame.coded_error));
     }
   }
 
   if (cpi->common.frame_type == KEY_FRAME)
     target = vp9_rc_clamp_iframe_target_size(cpi, rc->this_frame_target);
   else
     target = vp9_rc_clamp_pframe_target_size(cpi, rc->this_frame_target);
   vp9_rc_set_frame_target(cpi, target);
 
-  // Update the total stats remaining structure
+  // Update the total stats remaining structure.
   subtract_stats(&twopass->total_left_stats, &this_frame);
 }
 
 void vp9_twopass_postencode_update(VP9_COMP *cpi, uint64_t bytes_used) {
 #ifdef DISABLE_RC_LONG_TERM_MEM
   cpi->twopass.bits_left -=  cpi->rc.this_frame_target;
 #else
   cpi->twopass.bits_left -= 8 * bytes_used;
   // Update bits left to the kf and gf groups to account for overshoot or
-  // undershoot on these frames
+  // undershoot on these frames.
   if (cm->frame_type == KEY_FRAME) {
     cpi->twopass.kf_group_bits += cpi->rc.this_frame_target -
         cpi->rc.projected_frame_size;
 
     cpi->twopass.kf_group_bits = MAX(cpi->twopass.kf_group_bits, 0);
   } else if (cpi->refresh_golden_frame || cpi->refresh_alt_ref_frame) {
     cpi->twopass.gf_group_bits += cpi->rc.this_frame_target -
         cpi->rc.projected_frame_size;
 
     cpi->twopass.gf_group_bits = MAX(cpi->twopass.gf_group_bits, 0);
   }
 #endif
 }