Implemented the GetSources() in native code.

webrtc/api/rtpreceiverinterface.h

Index: webrtc/api/rtpreceiverinterface.h
diff --git a/webrtc/api/rtpreceiverinterface.h b/webrtc/api/rtpreceiverinterface.h
index 8607d935a232be6364327ad0af4d966280ec65c4..59c93db4e6fe8c5d607494d326439416ee60980c 100644
--- a/webrtc/api/rtpreceiverinterface.h
+++ b/webrtc/api/rtpreceiverinterface.h
@@ -14,7 +14,9 @@
 #ifndef WEBRTC_API_RTPRECEIVERINTERFACE_H_
 #define WEBRTC_API_RTPRECEIVERINTERFACE_H_
 
+#include <memory>
 #include <string>
+#include <vector>
 
 #include "webrtc/api/mediatypes.h"
 #include "webrtc/api/mediastreaminterface.h"
@@ -25,6 +27,20 @@
 
 namespace webrtc {
 
+struct RtpContributingSource {
+  RtpContributingSource() : timestamp(0), source(0) {}
+
+  RtpContributingSource(int64_t time, uint32_t src)
+      : timestamp(time), source(src) {}
+
+  int64_t timestamp;
+  // Can be either the SSRC or the CSRC.
+  uint32_t source;
+  // This isn't implemented yet and will always return an empty Optional.
+  // TODO(zhihuang): Implement this to return real audio level.
+  rtc::Optional<int8_t> audio_level;

[Taylor Brandstetter, 2017/03/31 22:10:50]

nit: I'd still be in favor of using getters/setters. For example: in the future
we could decide it would be helpful to return both the CSRC and the associated
SSRC in the same object. In which case it may change to:

// Returns the CSRC or SSRC depending on what the object represents.
uint32_t source() {
  return csrc_ ? *csrc_ : ssrc_;
}

uint32_t ssrc() { 
  return ssrc_;
}

private:

// Set if this object represents a CSRC, unset if it
// represents an SSRC.
rtc::Optional<uint32_t> csrc_;
uint32_t ssrc_;


If the data members were private, it would be easy to make this change.

[Zhi Huang, 2017/04/04 04:24:33]

Done.

+};
+
 class RtpReceiverObserverInterface {
  public:
   // Note: Currently if there are multiple RtpReceivers of the same media type,
@@ -61,6 +77,13 @@ class RtpReceiverInterface : public rtc::RefCountInterface {
   // Must call SetObserver(nullptr) before the observer is destroyed.
   virtual void SetObserver(RtpReceiverObserverInterface* observer) = 0;
 
+  // TODO(zhihuang): Remove the default implementation once the subclasses
+  // implement this. Currently, the only relevant subclass is the
+  // content::FakeRtpReceiver in Chromium.
+  virtual std::vector<RtpContributingSource> GetContributingSources() {
+    return std::vector<RtpContributingSource>();
+  }
+
  protected:
   virtual ~RtpReceiverInterface() {}
 };
@@ -76,7 +99,8 @@ BEGIN_SIGNALING_PROXY_MAP(RtpReceiver)
   PROXY_CONSTMETHOD0(RtpParameters, GetParameters);
   PROXY_METHOD1(bool, SetParameters, const RtpParameters&)
   PROXY_METHOD1(void, SetObserver, RtpReceiverObserverInterface*);
-END_PROXY_MAP()
+  PROXY_METHOD0(std::vector<RtpContributingSource>, GetContributingSources);
+  END_PROXY_MAP()
 
 }  // namespace webrtc