VP9 firstpass: Bugfix when mi_col_start/end is odd

Before this patch, if mi_col_end was odd, then the for loop for 'mb_col'
was looping once LESS than it should have been.

For example, if mi_col_end = 47, then the loop was terminating when
mb_col == 23. However, the correct behavior would be to terminate  when
mb_col == 24.

The issue was introduced in:
https://chromium-review.googlesource.com/c/webm/libvpx/+/423279

This can lead to many of the stats being inaccurate, for such videos
(with mi_col_start/end having an odd value).

As an example:
Even for very static content, fp_acc_data->intercount can never reach the
same value as num_mbs. And in turn, pcnt_inter can never reach the value 1
(that is, 100%). This would lead to very static videos NOT being marked
static, and encoded like regular videos.

Note: this is just one possible effect based on observation. Other
issues are also possible based on other stats.

Improvement on some test clips:
-------------------------------
- One test clip saw a gain of -2.580% in VBR mode (and -3.153% in Q
mode). The reason for improvement: a wrongly detected scene cut was
avoided due to corrected value in 'this_frame->pcnt_inter'.
- Some very static clips correctly marked as having 100% zero motion.
This avoided addition of unncecessary alt-refs, thereby reducing the
bitrate.

BDRate (PSNR) on regular sets (VBR mode):
-----------------------------------------
lowres: 0.0
midres: -0.027 (some clips were better/worse, but I double checked that
changes were as expected, given correction in stats calculation).
hdres: 0.0

STATS_CHANGED for the types of videos described above.

Change-Id: Ifbc2c0c0815d23ec4015475680bdf8886f158dcc

diff --git a/vp9/encoder/vp9_firstpass.c b/vp9/encoder/vp9_firstpass.c
index 03ac934632c21fb6519ddac8ef2e222b1d9edb2b..8f0da48a2a10f78bca0074a96f1f08855446d317 100644 (file)
--- a/vp9/encoder/vp9_firstpass.c
+++ b/vp9/encoder/vp9_firstpass.c
@@ -820,6 +820,8 @@ void vp9_first_pass_encode_tile_mb_row(VP9_COMP *cpi, ThreadData *td,
   VP9_COMMON *const cm = &cpi->common;
   MACROBLOCKD *const xd = &x->e_mbd;
   TileInfo tile = tile_data->tile_info;
+  const int mb_col_start = ROUND_POWER_OF_TWO(tile.mi_col_start, 1);
+  const int mb_col_end = ROUND_POWER_OF_TWO(tile.mi_col_end, 1);
   struct macroblock_plane *const p = x->plane;
   struct macroblockd_plane *const pd = xd->plane;
   const PICK_MODE_CONTEXT *ctx = &td->pc_root->none;
@@ -846,9 +848,8 @@ void vp9_first_pass_encode_tile_mb_row(VP9_COMP *cpi, ThreadData *td,
   assert(new_yv12 != NULL);
   assert(frame_is_intra_only(cm) || (lst_yv12 != NULL));
 
-  xd->mi = cm->mi_grid_visible + xd->mi_stride * (mb_row << 1) +
-           (tile.mi_col_start >> 1);
-  xd->mi[0] = cm->mi + xd->mi_stride * (mb_row << 1) + (tile.mi_col_start >> 1);
+  xd->mi = cm->mi_grid_visible + xd->mi_stride * (mb_row << 1) + mb_col_start;
+  xd->mi[0] = cm->mi + xd->mi_stride * (mb_row << 1) + mb_col_start;
 
   for (i = 0; i < MAX_MB_PLANE; ++i) {
     p[i].coeff = ctx->coeff_pbuf[i][1];
@@ -862,10 +863,9 @@ void vp9_first_pass_encode_tile_mb_row(VP9_COMP *cpi, ThreadData *td,
   uv_mb_height = 16 >> (new_yv12->y_height > new_yv12->uv_height);
 
   // Reset above block coeffs.
-  recon_yoffset =
-      (mb_row * recon_y_stride * 16) + (tile.mi_col_start >> 1) * 16;
-  recon_uvoffset = (mb_row * recon_uv_stride * uv_mb_height) +
-                   (tile.mi_col_start >> 1) * uv_mb_height;
+  recon_yoffset = (mb_row * recon_y_stride * 16) + mb_col_start * 16;
+  recon_uvoffset =
+      (mb_row * recon_uv_stride * uv_mb_height) + mb_col_start * uv_mb_height;
 
   // Set up limit values for motion vectors to prevent them extending
   // outside the UMV borders.
@@ -873,8 +873,7 @@ void vp9_first_pass_encode_tile_mb_row(VP9_COMP *cpi, ThreadData *td,
   x->mv_limits.row_max =
       ((cm->mb_rows - 1 - mb_row) * 16) + BORDER_MV_PIXELS_B16;
 
-  for (mb_col = tile.mi_col_start >> 1, c = 0; mb_col < (tile.mi_col_end >> 1);
-       ++mb_col, c++) {
+  for (mb_col = mb_col_start, c = 0; mb_col < mb_col_end; ++mb_col, c++) {
     int this_error;
     int this_intra_error;
     const int use_dc_pred = (mb_col || mb_row) && (!mb_col || !mb_row);
@@ -920,7 +919,7 @@ void vp9_first_pass_encode_tile_mb_row(VP9_COMP *cpi, ThreadData *td,
     x->skip_encode = 0;
     x->fp_src_pred = 0;
     // Do intra prediction based on source pixels for tile boundaries
-    if ((mb_col == (tile.mi_col_start >> 1)) && mb_col != 0) {
+    if (mb_col == mb_col_start && mb_col != 0) {
       xd->left_mi = &mi_left;
       x->fp_src_pred = 1;
     }
@@ -1310,7 +1309,7 @@ void vp9_first_pass_encode_tile_mb_row(VP9_COMP *cpi, ThreadData *td,
     recon_uvoffset += uv_mb_height;
 
     // Accumulate row level stats to the corresponding tile stats
-    if (cpi->row_mt && mb_col == (tile.mi_col_end >> 1) - 1)
+    if (cpi->row_mt && mb_col == mb_col_end - 1)
       accumulate_fp_mb_row_stat(tile_data, fp_acc_data);
 
     (*(cpi->row_mt_sync_write_ptr))(&tile_data->row_mt_sync, mb_row, c,