Added configurable offsets to the per-packet overhead in ANA.

modules/audio_coding/audio_network_adaptor/bitrate_controller.cc

Index: modules/audio_coding/audio_network_adaptor/bitrate_controller.cc
diff --git a/modules/audio_coding/audio_network_adaptor/bitrate_controller.cc b/modules/audio_coding/audio_network_adaptor/bitrate_controller.cc
index 587c858ece27c6cf16f2931492008c2e802a3827..16c4bc4e556b2b89dadad9bfe65236ad34ea0928 100644
--- a/modules/audio_coding/audio_network_adaptor/bitrate_controller.cc
+++ b/modules/audio_coding/audio_network_adaptor/bitrate_controller.cc
@@ -19,9 +19,13 @@ namespace webrtc {
 namespace audio_network_adaptor {
 
 BitrateController::Config::Config(int initial_bitrate_bps,
-                                  int initial_frame_length_ms)
+                                  int initial_frame_length_ms,
+                                  int fl_increase_overhead_offset,
+                                  int fl_decrease_overhead_offset)
     : initial_bitrate_bps(initial_bitrate_bps),
-      initial_frame_length_ms(initial_frame_length_ms) {}
+      initial_frame_length_ms(initial_frame_length_ms),
+      fl_increase_overhead_offset(fl_increase_overhead_offset),
+      fl_decrease_overhead_offset(fl_decrease_overhead_offset) {}
 
 BitrateController::Config::~Config() = default;
 
@@ -54,9 +58,15 @@ void BitrateController::MakeDecision(AudioEncoderRuntimeConfig* config) {
         webrtc::field_trial::IsEnabled("WebRTC-SendSideBwe-WithOverhead"));
     if (config->frame_length_ms)
       frame_length_ms_ = *config->frame_length_ms;
-    int overhead_rate_bps =
-        static_cast<int>(*overhead_bytes_per_packet_ * 8 * 1000 /
-            frame_length_ms_);
+    int offset = config->last_fl_change_increase
+                     ? config_.fl_increase_overhead_offset
+                     : config_.fl_decrease_overhead_offset;
+    // Check that
+    // -(*overhead_bytes_per_packet_) <= offset <= (*overhead_bytes_per_packet_)
+    RTC_DCHECK_GE(*overhead_bytes_per_packet_, -offset);
+    RTC_DCHECK_LE(offset, *overhead_bytes_per_packet_);
+    int overhead_rate_bps = static_cast<int>(
+        (*overhead_bytes_per_packet_ + offset) * 8 * 1000 / frame_length_ms_);
     bitrate_bps_ = std::max(0, *target_audio_bitrate_bps_ - overhead_rate_bps);
   }
   config->bitrate_bps = rtc::Optional<int>(bitrate_bps_);