diff --git a/vp9/encoder/vp9_encodeframe.c b/vp9/encoder/vp9_encodeframe.c
index bdaf4b98960e13eee53a4edf7248a043e19a5778..d1ecdf0f6ea3f3cb8e343c03f2c346aaac49f03c 100644
--- a/vp9/encoder/vp9_encodeframe.c
+++ b/vp9/encoder/vp9_encodeframe.c
@@ -572,9 +572,12 @@ static void pick_sb_modes(VP9_COMP *cpi, int mi_row, int mi_col,
 
   x->rd_search = 1;
 
-  if (bsize < BLOCK_SIZE_SB8X8)
+  if (bsize < BLOCK_SIZE_SB8X8) {
+    // When ab_index = 0 all sub-blocks are handled, so for ab_index != 0
+    // there is nothing to be done.
     if (xd->ab_index != 0)
       return;
+  }
 
   set_offsets(cpi, mi_row, mi_col, bsize);
   xd->mode_info_context->mbmi.sb_type = bsize;
@@ -632,7 +635,7 @@ static void update_stats(VP9_COMP *cpi) {
 }
 
 // TODO(jingning): the variables used here are little complicated. need further
-// refactoring on organizing the the temporary buffers, when recursive
+// refactoring on organizing the temporary buffers, when recursive
 // partition down to 4x4 block size is enabled.
 static PICK_MODE_CONTEXT *get_block_context(MACROBLOCK *x,
                                             BLOCK_SIZE_TYPE bsize) {
@@ -766,9 +769,12 @@ static void encode_b(VP9_COMP *cpi, TOKENEXTRA **tp, int mi_row, int mi_col,
   if (sub_index != -1)
     *(get_sb_index(xd, bsize)) = sub_index;
 
-  if (bsize < BLOCK_SIZE_SB8X8)
+  if (bsize < BLOCK_SIZE_SB8X8) {
+    // When ab_index = 0 all sub-blocks are handled, so for ab_index != 0
+    // there is nothing to be done.
     if (xd->ab_index > 0)
       return;
+  }
   set_offsets(cpi, mi_row, mi_col, bsize);
   update_state(cpi, get_block_context(x, bsize), bsize, output_enabled);
   encode_superblock(cpi, tp, output_enabled, mi_row, mi_col, bsize);
@@ -1223,6 +1229,8 @@ static void rd_use_partition(VP9_COMP *cpi, MODE_INFO *m, TOKENEXTRA **tp,
   subsize = get_subsize(bsize, partition);
 
   if (bsize < BLOCK_SIZE_SB8X8) {
+    // When ab_index = 0 all sub-blocks are handled, so for ab_index != 0
+    // there is nothing to be done.
     if (xd->ab_index != 0) {
       *rate = 0;
       *dist = 0;
@@ -1456,7 +1464,7 @@ static BLOCK_SIZE_TYPE max_partition_size[BLOCK_SIZE_TYPES] =
     BLOCK_64X64, BLOCK_64X64, BLOCK_64X64, BLOCK_64X64, BLOCK_64X64 };
 
 
-// Look at neighbouring blocks and set a min and max partition size based on
+// Look at neighboring blocks and set a min and max partition size based on
 // what they chose.
 static void rd_auto_partition_range(VP9_COMP *cpi,
                                     BLOCK_SIZE_TYPE * min_block_size,
@@ -1498,7 +1506,7 @@ static void rd_auto_partition_range(VP9_COMP *cpi,
 }
 
 // TODO(jingning,jimbankoski,rbultje): properly skip partition types that are
-// unlikely to be selected depending on previously rate-distortion optimization
+// unlikely to be selected depending on previous rate-distortion optimization
 // results, for encoding speed-up.
 static void rd_pick_partition(VP9_COMP *cpi, TOKENEXTRA **tp, int mi_row,
                               int mi_col, BLOCK_SIZE_TYPE bsize, int *rate,
@@ -1518,12 +1526,15 @@ static void rd_pick_partition(VP9_COMP *cpi, TOKENEXTRA **tp, int mi_row,
 
   (void) *tp_orig;
 
-  if (bsize < BLOCK_SIZE_SB8X8)
+  if (bsize < BLOCK_SIZE_SB8X8) {
+    // When ab_index = 0 all sub-blocks are handled, so for ab_index != 0
+    // there is nothing to be done.
     if (xd->ab_index != 0) {
       *rate = 0;
       *dist = 0;
       return;
     }
+  }
   assert(mi_height_log2(bsize) == mi_width_log2(bsize));
 
   save_context(cpi, mi_row, mi_col, a, l, sa, sl, bsize);
@@ -1941,8 +1952,7 @@ static void encode_sb_row(VP9_COMP *cpi, int mi_row, TOKENEXTRA **tp,
     } else {
       // If required set upper and lower partition size limits
       if (cpi->sf.auto_min_max_partition_size) {
-        rd_auto_partition_range(cpi,
-                                &cpi->sf.min_partition_size,
+        rd_auto_partition_range(cpi, &cpi->sf.min_partition_size,
                                 &cpi->sf.max_partition_size);
       }
 
diff --git a/vp9/encoder/vp9_rdopt.c b/vp9/encoder/vp9_rdopt.c
index fb3358e06df1de508bf9c148208fa72dc6aa5b52..0cf8f9b2a47fdba299b229cf948ed92fe20327dd 100644
--- a/vp9/encoder/vp9_rdopt.c
+++ b/vp9/encoder/vp9_rdopt.c
@@ -3448,7 +3448,7 @@ int64_t vp9_rd_pick_inter_mode_sb(VP9_COMP *cpi, MACROBLOCK *x,
       }
     }
 
-    // Select predictors
+    // Select prediction reference frames.
     for (i = 0; i < MAX_MB_PLANE; i++) {
       xd->plane[i].pre[0] = yv12_mb[ref_frame][i];
       if (comp_pred)
@@ -4043,7 +4043,7 @@ int64_t vp9_rd_pick_inter_mode_sb(VP9_COMP *cpi, MACROBLOCK *x,
          (cm->mcomp_filter_type == best_mbmode.interp_filter) ||
          (best_mbmode.ref_frame[0] == INTRA_FRAME));
 
-  // Updating rd_thresh_freq_fact[] here means that the differnt
+  // Updating rd_thresh_freq_fact[] here means that the different
   // partition/block sizes are handled independently based on the best
   // choice for the current partition. It may well be better to keep a scaled
   // best rd so far value and update rd_thresh_freq_fact based on the mode/size