Get VideoCapturer stats via VideoTrackSourceInterface in StatsCollector,

webrtc/api/rtpsenderinterface.h

 /*
  *  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.
  */
 
 // This file contains interfaces for RtpSenders
 // http://w3c.github.io/webrtc-pc/#rtcrtpsender-interface
 
 #ifndef WEBRTC_API_RTPSENDERINTERFACE_H_
 #define WEBRTC_API_RTPSENDERINTERFACE_H_
 
 #include <string>
 
 #include "webrtc/api/mediastreaminterface.h"
 #include "webrtc/api/proxy.h"
 #include "webrtc/api/rtpparameters.h"
+#include "webrtc/api/statstypes.h"
 #include "webrtc/base/refcount.h"
 #include "webrtc/base/scoped_ref_ptr.h"
 #include "webrtc/pc/mediasession.h"
 
 namespace webrtc {
 
 class RtpSenderInterface : public rtc::RefCountInterface {
  public:
   // Returns true if successful in setting the track.
   // Fails if an audio track is set on a video RtpSender, or vice-versa.
@@ skipping 16 matching lines @@
 
   // TODO(deadbeef): Support one sender having multiple stream ids.
   virtual void set_stream_id(const std::string& stream_id) = 0;
   virtual std::string stream_id() const = 0;
 
   virtual void Stop() = 0;
 
   virtual RtpParameters GetParameters() const = 0;
   virtual bool SetParameters(const RtpParameters& parameters) = 0;
 
+  // Returns a scoped_refptr(nullptr) if there are no stats.

[perkj_webrtc, 2016/03/29 11:03:39]

? StatsReport::Id is a scoped_refptr?  

[nisse-webrtc, 2016/03/29 11:37:31]

Yes, defined in statstypes.h as

  typedef rtc::scoped_refptr<IdBase> Id;

+  virtual StatsReport::Id stats_id() = 0;
+  virtual void ReportStats(StatsReport* report) = 0;

[perkj_webrtc, 2016/03/29 11:03:39]

Prefer GetStats anyway (saw your comments) since its widely used in the code
base for stats. 

[nisse-webrtc, 2016/03/29 11:37:31]

Most other GetStats methods either take an observer, or they work with a plain
struct. But I'll rename it if you really want.

I think StatsReport is a too opaque type to be used for anything not directly
tied to StatsCollector. E.g., if you write test cases related to the stats for
some component, it's going to be annoying and error prone to have to access the
produced stats via StatsReport::FindValue(StatsReport::kSomething).int_val(),
not to speak about error checking needed if you want the testcase to report the
precise problem rather than crash.

[tommi, 2016/03/30 11:46:45]

Is this method's implementation expected to block at any time?  If so, should it
be designed to be async? (as GetStats is)

[nisse-webrtc, 2016/03/30 12:09:31]

It shouldn't block. If the RtpSender is connected to a camera, it ends up in
cricket::VideoCapturer::GetStats which returns the size of the most recent
captured frame (after taking the frame_stats_crit_ lock, which only competes
with UpdateStats). In all other cases, it does nothing.

+
  protected:
   virtual ~RtpSenderInterface() {}
 };
 
 // Define proxy for RtpSenderInterface.
 BEGIN_PROXY_MAP(RtpSender)
 PROXY_METHOD1(bool, SetTrack, MediaStreamTrackInterface*)
 PROXY_CONSTMETHOD0(rtc::scoped_refptr<MediaStreamTrackInterface>, track)
 PROXY_METHOD1(void, SetSsrc, uint32_t)
 PROXY_CONSTMETHOD0(uint32_t, ssrc)
 PROXY_CONSTMETHOD0(cricket::MediaType, media_type)
 PROXY_CONSTMETHOD0(std::string, id)
 PROXY_METHOD1(void, set_stream_id, const std::string&)
 PROXY_CONSTMETHOD0(std::string, stream_id)
 PROXY_METHOD0(void, Stop)
 PROXY_CONSTMETHOD0(RtpParameters, GetParameters);
 PROXY_METHOD1(bool, SetParameters, const RtpParameters&)
+PROXY_METHOD0(StatsReport::Id, stats_id)
+PROXY_METHOD1(void, ReportStats, StatsReport*)

[tommi, 2016/03/30 11:46:45]

as is, all proxy methods involve a synchronous thread hop.  This is unfortunate
and I'd like for us to design the APIs with more asynchronicity in mind.

 END_PROXY()
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_API_RTPSENDERINTERFACE_H_