Default disables legacy overhead calculation.

This ensures that overhead calculation is correct by default when
enabling the WebRTC-SendSideBwe-WithOverhead field trial.

We keep the legacy mode to allow downstream projects already relying on
WebRTC-SendSideBwe-WithOverhead to preserve the current behavior.

Bug: webrtc:6762
Change-Id: I84369c760d59345a48ec352997dbed6d2db21d13
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/167862
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Reviewed-by: Sam Zackrisson <saza@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30424}

Author: jonex

audio/audio_send_stream.cc

@@ -154,7 +154,7 @@ AudioSendStream::AudioSendStream(
       channel_send_(std::move(channel_send)),
       event_log_(event_log),
       use_legacy_overhead_calculation_(
-          !field_trial::IsDisabled("WebRTC-Audio-LegacyOverhead")),
+          field_trial::IsEnabled("WebRTC-Audio-LegacyOverhead")),
       bitrate_allocator_(bitrate_allocator),
       rtp_transport_(rtp_transport),
       rtp_rtcp_module_(channel_send_->GetRtpRtcp()),

modules/pacing/pacing_controller.cc

@@ -100,7 +100,7 @@ PacingController::PacingController(Clock* clock,
       small_first_probe_packet_(
           IsEnabled(*field_trials_, "WebRTC-Pacer-SmallFirstProbePacket")),
       ignore_transport_overhead_(
-          !IsDisabled(*field_trials_, "WebRTC-Pacer-IgnoreTransportOverhead")),
+          IsEnabled(*field_trials_, "WebRTC-Pacer-IgnoreTransportOverhead")),
       min_packet_limit_(kDefaultMinPacketLimit),
       transport_overhead_per_packet_(DataSize::Zero()),
       last_timestamp_(clock_->CurrentTime()),

modules/pacing/round_robin_packet_queue.cc

@@ -260,6 +260,15 @@ void RoundRobinPacketQueue::SetIncludeOverhead() {
 }
 
 void RoundRobinPacketQueue::SetTransportOverhead(DataSize overhead_per_packet) {
+  if (include_overhead_) {
+    DataSize previous_overhead = transport_overhead_per_packet_;
+    // We need to update the size to reflect overhead for existing packets.
+    for (const auto& stream : streams_) {
+      int packets = stream.second.packet_queue.size();
+      size_ -= packets * previous_overhead;
+      size_ += packets * overhead_per_packet;
+    }
+  }
   transport_overhead_per_packet_ = overhead_per_packet;
 }