Modify lag_in_frames slightly for better coding performance

STATS_CHANGED

Change-Id: Ia5d34b5003775ac22e3ccf7a7614a72eea23a0c4

av1/av1_cx_iface.c

diff --git a/av1/av1_cx_iface.c b/av1/av1_cx_iface.c
index eb510eb..f494b2b 100644
--- a/av1/av1_cx_iface.c
+++ b/av1/av1_cx_iface.c
@@ -1365,6 +1365,13 @@
 #else
   gf_cfg->lag_in_frames = clamp(cfg->g_lag_in_frames, 0, MAX_LAG_BUFFERS);
 #endif
+
+  // Modify lag_in_frames slightly for better coding performance (e.g. better
+  // temporal filtering result).
+  if (oxcf->mode == GOOD && gf_cfg->lag_in_frames >= 32 &&
+      gf_cfg->lag_in_frames < 39)
+    gf_cfg->lag_in_frames = clamp(39, 0, MAX_LAG_BUFFERS);
+
   gf_cfg->enable_auto_arf = extra_cfg->enable_auto_alt_ref;
   gf_cfg->enable_auto_brf = extra_cfg->enable_auto_bwd_ref;
   gf_cfg->min_gf_interval = extra_cfg->min_gf_interval;