From: John Koleszar <jkoleszar@google.com>
Date: Fri, 18 Jan 2013 22:35:20 +0000 (-0800)
Subject: Use alt-ref frame context for keyframes
X-Git-Tag: v1.3.0~1151^2~240^2
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=2f24ad9e85e4db0d9d5b265a6d4c1f4b7db6babb;p=libvpx

Use alt-ref frame context for keyframes

This matches the behavior prior to generalizing the frame context
selection, and intuitively makes sense in that the first forward ref
is immediately after the keyframe, so it's quality is improved a bit
by using the keyframe's entropy context rather than the default.

Change-Id: Ia82cef79382b9d8cfafdc44ba0533d4dc3e44053
---

diff --git a/vp9/encoder/vp9_ratectrl.c b/vp9/encoder/vp9_ratectrl.c
index b5e5fec2f..be87326a0 100644
--- a/vp9/encoder/vp9_ratectrl.c
+++ b/vp9/encoder/vp9_ratectrl.c
@@ -286,6 +286,13 @@ void vp9_setup_key_frame(VP9_COMP *cpi) {
                sizeof(xd->mb_mv_ref_probs));
   }
 #endif
+
+  /* Choose which entropy context to use. When using a forward reference
+   * frame, it immediately follows the keyframe, and thus benefits from
+   * using the same entropy context established by the keyframe. Otherwise,
+   * use the default context 0.
+   */
+  cm->frame_context_idx = cpi->oxcf.play_alternate;
 }
 
 void vp9_setup_inter_frame(VP9_COMP *cpi) {