Forward the SignalFirstPacketReceived to RtpReceiver.

webrtc/api/rtpreceiver.cc

 /*
  *  Copyright 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 11 matching lines @@
                                    const std::string& track_id,
                                    uint32_t ssrc,
                                    AudioProviderInterface* provider)
     : id_(track_id),
       ssrc_(ssrc),
       provider_(provider),
       track_(AudioTrackProxy::Create(
           rtc::Thread::Current(),
           AudioTrack::Create(track_id,
                              RemoteAudioSource::Create(ssrc, provider)))),
-      cached_track_enabled_(track_->enabled()) {
+      cached_track_enabled_(track_->enabled()),
+      observer_(nullptr) {

[pthatcher1, 2016/06/08 17:35:55]

You don't need this if you use "= nullptr" in the other spot.

   RTC_DCHECK(track_->GetSource()->remote());
   track_->RegisterObserver(this);
   track_->GetSource()->RegisterAudioObserver(this);
   Reconfigure();
   stream->AddTrack(track_);
+  provider_->SignalFirstAudioPacketReceived.connect(
+      this, &AudioRtpReceiver::OnFirstAudioPacketReceived);
 }
 
 AudioRtpReceiver::~AudioRtpReceiver() {
   track_->GetSource()->UnregisterAudioObserver(this);
   track_->UnregisterObserver(this);
   Stop();
 }
 
 void AudioRtpReceiver::OnChanged() {
   if (cached_track_enabled_ != track_->enabled()) {
@@ skipping 28 matching lines @@
   return provider_->SetAudioRtpReceiveParameters(ssrc_, parameters);
 }
 
 void AudioRtpReceiver::Reconfigure() {
   if (!provider_) {
     return;
   }
   provider_->SetAudioPlayout(ssrc_, track_->enabled());
 }
 
+void AudioRtpReceiver::SetObserver(RtpReceiverObserverInterface* observer) {
+  observer_ = observer;
+  // If received the first packet before setting the observer, call the
+  // observer.
+  if (received_first_packet_) {
+    observer_->OnFirstPacketReceived(cricket::MEDIA_TYPE_AUDIO);
+  }
+}
+
+void AudioRtpReceiver::OnFirstAudioPacketReceived() {
+  if (observer_) {
+    observer_->OnFirstPacketReceived(cricket::MEDIA_TYPE_AUDIO);
+  }
+  received_first_packet_ = true;

[pthatcher1, 2016/06/08 17:35:55]

Do you have a unit test that covers setting the observer after the signal has
fired?  You could do so by simply setting a new observer after it's fired and
then seeing if the second observer fired.  

+}
+
 VideoRtpReceiver::VideoRtpReceiver(MediaStreamInterface* stream,
                                    const std::string& track_id,
                                    rtc::Thread* worker_thread,
                                    uint32_t ssrc,
                                    VideoProviderInterface* provider)
     : id_(track_id),
       ssrc_(ssrc),
       provider_(provider),
       source_(new RefCountedObject<VideoTrackSource>(&broadcaster_,
                                                      true /* remote */)),
       track_(VideoTrackProxy::Create(
           rtc::Thread::Current(),
           worker_thread,
           VideoTrack::Create(
               track_id,
               VideoTrackSourceProxy::Create(rtc::Thread::Current(),
                                             worker_thread,
-                                            source_)))) {
+                                            source_)))),
+      observer_(nullptr) {
   source_->SetState(MediaSourceInterface::kLive);
   provider_->SetVideoPlayout(ssrc_, true, &broadcaster_);
   stream->AddTrack(track_);
+  provider_->SignalFirstVideoPacketReceived.connect(
+      this, &VideoRtpReceiver::OnFirstVideoPacketReceived);
 }
 
 VideoRtpReceiver::~VideoRtpReceiver() {
   // Since cricket::VideoRenderer is not reference counted,
   // we need to remove it from the provider before we are deleted.
   Stop();
 }
 
 void VideoRtpReceiver::Stop() {
   // TODO(deadbeef): Need to do more here to fully stop receiving packets.
   if (!provider_) {
     return;
   }
   source_->SetState(MediaSourceInterface::kEnded);
   source_->OnSourceDestroyed();
   provider_->SetVideoPlayout(ssrc_, false, nullptr);
   provider_ = nullptr;
 }
 
 RtpParameters VideoRtpReceiver::GetParameters() const {
   return provider_->GetVideoRtpReceiveParameters(ssrc_);
 }
 
 bool VideoRtpReceiver::SetParameters(const RtpParameters& parameters) {
   TRACE_EVENT0("webrtc", "VideoRtpReceiver::SetParameters");
   return provider_->SetVideoRtpReceiveParameters(ssrc_, parameters);
 }
 
+void VideoRtpReceiver::SetObserver(RtpReceiverObserverInterface* observer) {
+  observer_ = observer;
+  // If received the first packet before setting the observer, call the
+  // observer.
+  if (received_first_packet_) {
+    observer_->OnFirstPacketReceived(cricket::MEDIA_TYPE_VIDEO);
+  }
+}
+
+void VideoRtpReceiver::OnFirstVideoPacketReceived() {
+  if (observer_) {
+    observer_->OnFirstPacketReceived(cricket::MEDIA_TYPE_VIDEO);

[pthatcher1, 2016/06/08 17:35:55]

Might as well add a media_type() getter to the RtpReceiver so that you can just
do media_type() here instead of duplicating MEDIA_TYPE_VIDEO.

Also, this might allow having shared code with a common RtpReceiverBase, which
Taylor is planning on adding.

[Zhi Huang, 2016/06/09 00:37:36]

Done.

+  }
+  received_first_packet_ = true;
+}
+
 }  // namespace webrtc