Use above/left (instead of previous in scan-order) as token context.

Pearson correlation for above or left is significantly higher than for
previous-in-scan-order (absolute values depend on position in scan, but
in general, we gain about 0.1-0.2 by using either above or left; using
both basically just makes this even better). For eob branch skipping,
we continue to use the previous token in scan order.

This helps about 0.9% on derf after re-training on a limited data set.
Full re-training and results on larger-resolution clips are pending.

Note that this commit breaks trellis, so we can probably get further
gains out of it by fixing trellis at some later point.

Change-Id: Iead68e296fc3a105cca746b5e3da9555d6010cfe

1 files changed, 1 insertions, 1 deletions

diff --git a/vp9/encoder/vp9_tokenize.h b/vp9/encoder/vp9_tokenize.h
index 464d7caf6..907f814ac 100644
--- a/vp9/encoder/vp9_tokenize.h
+++ b/vp9/encoder/vp9_tokenize.h
@@ -29,7 +29,7 @@ typedef struct {
 } TOKENEXTRA;
 
 typedef int64_t vp9_coeff_accum[REF_TYPES][COEF_BANDS][PREV_COEF_CONTEXTS]
-                               [MAX_ENTROPY_TOKENS];
+                               [MAX_ENTROPY_TOKENS + 1];
 
 int vp9_mby_is_skippable_4x4(MACROBLOCKD *xd);
 int vp9_mbuv_is_skippable_4x4(MACROBLOCKD *xd);