Fix short first kf bug.

This change is in response to quality issue in b/112953058

The quality regression observed is a result of a bug that manifested
because of a very short key frame group at the start of a chunk.
The group was so short that it was less than the minimum allowed
length of an ARF group, so the initial group was coded as a GF only
group. However, group length was not set correctly and the result
was a frame coded with a target of 0 bits.

This causes two problems:

Firstly one very poor frame that caused the issue to be raised.

Secondly that one  frame obviously overshoots its 0 target very heavily
and this has the effect moving the needle significantly in terms of the
adaptive rate control (specifically the estimate of bits per macro block
used to estimate the active Q range). Consequently there is undershoot
for most of the rest of the chunk and the overall rate ends up much lower
than the target (14Mb/s vs a target of 22Mb/s). (The sharp drop in the
overall rate is also noted in the issue.

BUG=b/112953058

Change-Id: Ide9cce57acd3dee0f9496b752902e7b4735f2c7f

diff --git a/vp9/encoder/vp9_firstpass.c b/vp9/encoder/vp9_firstpass.c
index 38e1d37cc4b2d4a060467ea35399c3d9353340fe..70953be9b71c96076db9b048e0b2aa8935464a26 100644 (file)
--- a/vp9/encoder/vp9_firstpass.c
+++ b/vp9/encoder/vp9_firstpass.c
@@ -3002,11 +3002,7 @@ static void define_gf_group(VP9_COMP *cpi, FIRSTPASS_STATS *this_frame) {
   rc->gfu_boost = VPXMIN((int)rc->gfu_boost, i * 200);
 #endif
 
-  rc->baseline_gf_interval =
-      ((twopass->kf_zeromotion_pct >= STATIC_KF_GROUP_THRESH) &&
-       (i >= rc->frames_to_key))
-          ? i
-          : (i - (is_key_frame || rc->source_alt_ref_pending));
+  rc->baseline_gf_interval = i - rc->source_alt_ref_pending;
 
   // TODO(zoeliu): Turn on the option to disable extra ALTREFs for still GF
   //               groups.