rtc: Adjust condition to set rps frame.

This has some improvement for RPS, comes from the CL:
https://aomedia-review.googlesource.com/c/aom/+/200501

Change-Id: I3272c88ee5e4376434e974b7f7eb5dea636586ab

av1/encoder/ratectrl.c

diff --git a/av1/encoder/ratectrl.c b/av1/encoder/ratectrl.c
index e752568..b1c68d8 100644
--- a/av1/encoder/ratectrl.c
+++ b/av1/encoder/ratectrl.c
@@ -3700,8 +3700,8 @@
 
 // Set to true if this frame is a recovery frame, for 1 layer RPS,
 // and whether we should apply some boost (QP, adjust speed features, etc).
-// Recovery frame here means frame whose closest reference suddenly
-// switched from previous frame to one much further away.
+// Recovery frame here means frame whose closest reference is x frames away,
+// where x = 4.
 // TODO(marpan): Consider adding on/off flag to SVC_REF_FRAME_CONFIG to
 // allow more control for applications.
 static bool set_flag_rps_bias_recovery_frame(const AV1_COMP *const cpi) {
@@ -3711,8 +3711,8 @@
       cpi->ppi->rtc_ref.reference_was_previous_frame) {
     int min_dist = av1_svc_get_min_ref_dist(cpi);
     // Only consider boost for this frame if its closest reference is further
-    // than x frames away, using x = 4 for now.
-    if (min_dist != INT_MAX && min_dist > 4) return true;
+    // than or equal to x frames away, using x = 4 for now.
+    if (min_dist != INT_MAX && min_dist >= 4) return true;
   }
   return false;
 }

av1/encoder/svc_layercontext.c

diff --git a/av1/encoder/svc_layercontext.c b/av1/encoder/svc_layercontext.c
index 79ef8db..7ac5d5a 100644
--- a/av1/encoder/svc_layercontext.c
+++ b/av1/encoder/svc_layercontext.c
@@ -699,8 +699,8 @@
   for (unsigned int i = 0; i < INTER_REFS_PER_FRAME; i++) {
     if (rtc_ref->reference[i]) {
       const int ref_frame_map_idx = rtc_ref->ref_idx[i];
-      const int dist =
-          current_frame_num - rtc_ref->buffer_time_index[ref_frame_map_idx];
+      const int dist = (1 + current_frame_num) -
+                       rtc_ref->buffer_time_index[ref_frame_map_idx];
       if (dist < min_dist) min_dist = dist;
     }
   }