Signals start rate when registering to TargetTransferRateObserver.

Bug: webrtc:10121
Change-Id: Ib608a98406d61225544d8b13bbcccb65c34e37f0
Reviewed-on: https://webrtc-review.googlesource.com/c/113814
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25983}

api/transport/network_control.h

@@ -23,6 +23,9 @@ class TargetTransferRateObserver {
   // Called to indicate target transfer rate as well as giving information about
   // the current estimate of network parameters.
   virtual void OnTargetTransferRate(TargetTransferRate) = 0;
+  // Called to provide updates to the expected target rate in case it changes
+  // before the first call to OnTargetTransferRate.
+  virtual void OnStartRateUpdate(DataRate) {}
 };
 
 // Configuration sent to factory create function. The parameters here are

call/bitrate_allocator.cc

@@ -77,6 +77,11 @@ BitrateAllocator::~BitrateAllocator() {
                            num_pause_events_);
 }
 
+void BitrateAllocator::UpdateStartRate(uint32_t start_rate_bps) {
+  RTC_DCHECK_CALLED_SEQUENTIALLY(&sequenced_checker_);
+  last_non_zero_bitrate_bps_ = start_rate_bps;
+}
+
 // static
 uint8_t BitrateAllocator::GetTransmissionMaxBitrateMultiplier() {
   uint64_t multiplier = strtoul(webrtc::field_trial::FindFullName(

call/bitrate_allocator.h

@@ -100,6 +100,8 @@ class BitrateAllocator : public BitrateAllocatorInterface {
   explicit BitrateAllocator(LimitObserver* limit_observer);
   ~BitrateAllocator() override;
 
+  void UpdateStartRate(uint32_t start_rate_bps);
+
   // Allocate target_bitrate across the registered BitrateAllocatorObservers.
   void OnNetworkChanged(uint32_t target_bitrate_bps,
                         uint32_t link_capacity_bps,

call/call.cc

@@ -215,6 +215,7 @@ class Call final : public webrtc::Call,
 
   // Implements TargetTransferRateObserver,
   void OnTargetTransferRate(TargetTransferRate msg) override;
+  void OnStartRateUpdate(DataRate start_rate) override;
 
   // Implements BitrateAllocator::LimitObserver.
   void OnAllocationLimitsChanged(uint32_t min_send_bitrate_bps,
@@ -1091,6 +1092,15 @@ void Call::OnSentPacket(const rtc::SentPacket& sent_packet) {
   transport_send_ptr_->OnSentPacket(sent_packet);
 }
 
+void Call::OnStartRateUpdate(DataRate start_rate) {
+  if (!transport_send_ptr_->GetWorkerQueue()->IsCurrent()) {
+    transport_send_ptr_->GetWorkerQueue()->PostTask(
+        [this, start_rate] { this->OnStartRateUpdate(start_rate); });
+    return;
+  }
+  bitrate_allocator_->UpdateStartRate(start_rate.bps<uint32_t>());
+}
+
 void Call::OnTargetTransferRate(TargetTransferRate msg) {
   // TODO(bugs.webrtc.org/9719)
   // Call::OnTargetTransferRate requires that on target transfer rate is invoked

call/rtp_transport_controller_send.cc

@@ -271,6 +271,7 @@ void RtpTransportControllerSend::RegisterTargetTransferRateObserver(
     RTC_DCHECK_RUN_ON(&task_queue_);
     RTC_DCHECK(observer_ == nullptr);
     observer_ = observer;
+    observer_->OnStartRateUpdate(*initial_config_.constraints.starting_rate);
     MaybeCreateControllers();
   });
 }