xref: /aosp_15_r20/external/webrtc/examples/unityplugin/simple_peer_connection.cc (revision d9f758449e529ab9291ac668be2861e7a55c2422)
1 /*
2  *  Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
3  *
4  *  Use of this source code is governed by a BSD-style license
5  *  that can be found in the LICENSE file in the root of the source
6  *  tree. An additional intellectual property rights grant can be found
7  *  in the file PATENTS.  All contributing project authors may
8  *  be found in the AUTHORS file in the root of the source tree.
9  */
10 
11 #include "examples/unityplugin/simple_peer_connection.h"
12 
13 #include <utility>
14 
15 #include "absl/memory/memory.h"
16 #include "api/audio_codecs/builtin_audio_decoder_factory.h"
17 #include "api/audio_codecs/builtin_audio_encoder_factory.h"
18 #include "api/create_peerconnection_factory.h"
19 #include "media/engine/internal_decoder_factory.h"
20 #include "media/engine/internal_encoder_factory.h"
21 #include "media/engine/multiplex_codec_factory.h"
22 #include "modules/audio_device/include/audio_device.h"
23 #include "modules/audio_processing/include/audio_processing.h"
24 #include "modules/video_capture/video_capture_factory.h"
25 #include "pc/video_track_source.h"
26 #include "test/vcm_capturer.h"
27 
28 #if defined(WEBRTC_ANDROID)
29 #include "examples/unityplugin/class_reference_holder.h"
30 #include "modules/utility/include/helpers_android.h"
31 #include "sdk/android/src/jni/android_video_track_source.h"
32 #include "sdk/android/src/jni/jni_helpers.h"
33 #endif
34 
35 // Names used for media stream ids.
36 const char kAudioLabel[] = "audio_label";
37 const char kVideoLabel[] = "video_label";
38 const char kStreamId[] = "stream_id";
39 
40 namespace {
41 static int g_peer_count = 0;
42 static std::unique_ptr<rtc::Thread> g_worker_thread;
43 static std::unique_ptr<rtc::Thread> g_signaling_thread;
44 static rtc::scoped_refptr<webrtc::PeerConnectionFactoryInterface>
45     g_peer_connection_factory;
46 #if defined(WEBRTC_ANDROID)
47 // Android case: the video track does not own the capturer, and it
48 // relies on the app to dispose the capturer when the peerconnection
49 // shuts down.
50 static jobject g_camera = nullptr;
51 #else
52 class CapturerTrackSource : public webrtc::VideoTrackSource {
53  public:
Create()54   static rtc::scoped_refptr<CapturerTrackSource> Create() {
55     const size_t kWidth = 640;
56     const size_t kHeight = 480;
57     const size_t kFps = 30;
58     const size_t kDeviceIndex = 0;
59     std::unique_ptr<webrtc::test::VcmCapturer> capturer = absl::WrapUnique(
60         webrtc::test::VcmCapturer::Create(kWidth, kHeight, kFps, kDeviceIndex));
61     if (!capturer) {
62       return nullptr;
63     }
64     return rtc::make_ref_counted<CapturerTrackSource>(std::move(capturer));
65   }
66 
67  protected:
CapturerTrackSource(std::unique_ptr<webrtc::test::VcmCapturer> capturer)68   explicit CapturerTrackSource(
69       std::unique_ptr<webrtc::test::VcmCapturer> capturer)
70       : VideoTrackSource(/*remote=*/false), capturer_(std::move(capturer)) {}
71 
72  private:
source()73   rtc::VideoSourceInterface<webrtc::VideoFrame>* source() override {
74     return capturer_.get();
75   }
76   std::unique_ptr<webrtc::test::VcmCapturer> capturer_;
77 };
78 
79 #endif
80 
GetEnvVarOrDefault(const char * env_var_name,const char * default_value)81 std::string GetEnvVarOrDefault(const char* env_var_name,
82                                const char* default_value) {
83   std::string value;
84   const char* env_var = getenv(env_var_name);
85   if (env_var)
86     value = env_var;
87 
88   if (value.empty())
89     value = default_value;
90 
91   return value;
92 }
93 
GetPeerConnectionString()94 std::string GetPeerConnectionString() {
95   return GetEnvVarOrDefault("WEBRTC_CONNECT", "stun:stun.l.google.com:19302");
96 }
97 
98 class DummySetSessionDescriptionObserver
99     : public webrtc::SetSessionDescriptionObserver {
100  public:
Create()101   static rtc::scoped_refptr<DummySetSessionDescriptionObserver> Create() {
102     return rtc::make_ref_counted<DummySetSessionDescriptionObserver>();
103   }
OnSuccess()104   virtual void OnSuccess() { RTC_LOG(LS_INFO) << __FUNCTION__; }
OnFailure(webrtc::RTCError error)105   virtual void OnFailure(webrtc::RTCError error) {
106     RTC_LOG(LS_INFO) << __FUNCTION__ << " " << ToString(error.type()) << ": "
107                      << error.message();
108   }
109 
110  protected:
DummySetSessionDescriptionObserver()111   DummySetSessionDescriptionObserver() {}
~DummySetSessionDescriptionObserver()112   ~DummySetSessionDescriptionObserver() {}
113 };
114 
115 }  // namespace
116 
InitializePeerConnection(const char ** turn_urls,const int no_of_urls,const char * username,const char * credential,bool is_receiver)117 bool SimplePeerConnection::InitializePeerConnection(const char** turn_urls,
118                                                     const int no_of_urls,
119                                                     const char* username,
120                                                     const char* credential,
121                                                     bool is_receiver) {
122   RTC_DCHECK(peer_connection_.get() == nullptr);
123 
124   if (g_peer_connection_factory == nullptr) {
125     g_worker_thread = rtc::Thread::Create();
126     g_worker_thread->Start();
127     g_signaling_thread = rtc::Thread::Create();
128     g_signaling_thread->Start();
129 
130     g_peer_connection_factory = webrtc::CreatePeerConnectionFactory(
131         g_worker_thread.get(), g_worker_thread.get(), g_signaling_thread.get(),
132         nullptr, webrtc::CreateBuiltinAudioEncoderFactory(),
133         webrtc::CreateBuiltinAudioDecoderFactory(),
134         std::unique_ptr<webrtc::VideoEncoderFactory>(
135             new webrtc::MultiplexEncoderFactory(
136                 std::make_unique<webrtc::InternalEncoderFactory>())),
137         std::unique_ptr<webrtc::VideoDecoderFactory>(
138             new webrtc::MultiplexDecoderFactory(
139                 std::make_unique<webrtc::InternalDecoderFactory>())),
140         nullptr, nullptr);
141   }
142   if (!g_peer_connection_factory.get()) {
143     DeletePeerConnection();
144     return false;
145   }
146 
147   g_peer_count++;
148   if (!CreatePeerConnection(turn_urls, no_of_urls, username, credential)) {
149     DeletePeerConnection();
150     return false;
151   }
152 
153   mandatory_receive_ = is_receiver;
154   return peer_connection_.get() != nullptr;
155 }
156 
CreatePeerConnection(const char ** turn_urls,const int no_of_urls,const char * username,const char * credential)157 bool SimplePeerConnection::CreatePeerConnection(const char** turn_urls,
158                                                 const int no_of_urls,
159                                                 const char* username,
160                                                 const char* credential) {
161   RTC_DCHECK(g_peer_connection_factory.get() != nullptr);
162   RTC_DCHECK(peer_connection_.get() == nullptr);
163 
164   local_video_observer_.reset(new VideoObserver());
165   remote_video_observer_.reset(new VideoObserver());
166 
167   // Add the turn server.
168   if (turn_urls != nullptr) {
169     if (no_of_urls > 0) {
170       webrtc::PeerConnectionInterface::IceServer turn_server;
171       for (int i = 0; i < no_of_urls; i++) {
172         std::string url(turn_urls[i]);
173         if (url.length() > 0)
174           turn_server.urls.push_back(turn_urls[i]);
175       }
176 
177       std::string user_name(username);
178       if (user_name.length() > 0)
179         turn_server.username = username;
180 
181       std::string password(credential);
182       if (password.length() > 0)
183         turn_server.password = credential;
184 
185       config_.servers.push_back(turn_server);
186     }
187   }
188 
189   // Add the stun server.
190   webrtc::PeerConnectionInterface::IceServer stun_server;
191   stun_server.uri = GetPeerConnectionString();
192   config_.servers.push_back(stun_server);
193 
194   auto result = g_peer_connection_factory->CreatePeerConnectionOrError(
195       config_, webrtc::PeerConnectionDependencies(this));
196   if (!result.ok()) {
197     peer_connection_ = nullptr;
198     return false;
199   }
200   peer_connection_ = result.MoveValue();
201   return true;
202 }
203 
DeletePeerConnection()204 void SimplePeerConnection::DeletePeerConnection() {
205   g_peer_count--;
206 
207 #if defined(WEBRTC_ANDROID)
208   if (g_camera) {
209     JNIEnv* env = webrtc::jni::GetEnv();
210     jclass pc_factory_class =
211         unity_plugin::FindClass(env, "org/webrtc/UnityUtility");
212     jmethodID stop_camera_method = webrtc::GetStaticMethodID(
213         env, pc_factory_class, "StopCamera", "(Lorg/webrtc/VideoCapturer;)V");
214 
215     env->CallStaticVoidMethod(pc_factory_class, stop_camera_method, g_camera);
216     CHECK_EXCEPTION(env);
217 
218     g_camera = nullptr;
219   }
220 #endif
221 
222   CloseDataChannel();
223   peer_connection_ = nullptr;
224   active_streams_.clear();
225 
226   if (g_peer_count == 0) {
227     g_peer_connection_factory = nullptr;
228     g_signaling_thread.reset();
229     g_worker_thread.reset();
230   }
231 }
232 
CreateOffer()233 bool SimplePeerConnection::CreateOffer() {
234   if (!peer_connection_.get())
235     return false;
236 
237   webrtc::PeerConnectionInterface::RTCOfferAnswerOptions options;
238   if (mandatory_receive_) {
239     options.offer_to_receive_audio = true;
240     options.offer_to_receive_video = true;
241   }
242   peer_connection_->CreateOffer(this, options);
243   return true;
244 }
245 
CreateAnswer()246 bool SimplePeerConnection::CreateAnswer() {
247   if (!peer_connection_.get())
248     return false;
249 
250   webrtc::PeerConnectionInterface::RTCOfferAnswerOptions options;
251   if (mandatory_receive_) {
252     options.offer_to_receive_audio = true;
253     options.offer_to_receive_video = true;
254   }
255   peer_connection_->CreateAnswer(this, options);
256   return true;
257 }
258 
OnSuccess(webrtc::SessionDescriptionInterface * desc)259 void SimplePeerConnection::OnSuccess(
260     webrtc::SessionDescriptionInterface* desc) {
261   peer_connection_->SetLocalDescription(
262       DummySetSessionDescriptionObserver::Create().get(), desc);
263 
264   std::string sdp;
265   desc->ToString(&sdp);
266 
267   if (OnLocalSdpReady)
268     OnLocalSdpReady(desc->type().c_str(), sdp.c_str());
269 }
270 
OnFailure(webrtc::RTCError error)271 void SimplePeerConnection::OnFailure(webrtc::RTCError error) {
272   RTC_LOG(LS_ERROR) << ToString(error.type()) << ": " << error.message();
273 
274   // TODO(hta): include error.type in the message
275   if (OnFailureMessage)
276     OnFailureMessage(error.message());
277 }
278 
OnIceCandidate(const webrtc::IceCandidateInterface * candidate)279 void SimplePeerConnection::OnIceCandidate(
280     const webrtc::IceCandidateInterface* candidate) {
281   RTC_LOG(LS_INFO) << __FUNCTION__ << " " << candidate->sdp_mline_index();
282 
283   std::string sdp;
284   if (!candidate->ToString(&sdp)) {
285     RTC_LOG(LS_ERROR) << "Failed to serialize candidate";
286     return;
287   }
288 
289   if (OnIceCandidateReady)
290     OnIceCandidateReady(sdp.c_str(), candidate->sdp_mline_index(),
291                         candidate->sdp_mid().c_str());
292 }
293 
RegisterOnLocalI420FrameReady(I420FRAMEREADY_CALLBACK callback)294 void SimplePeerConnection::RegisterOnLocalI420FrameReady(
295     I420FRAMEREADY_CALLBACK callback) {
296   if (local_video_observer_)
297     local_video_observer_->SetVideoCallback(callback);
298 }
299 
RegisterOnRemoteI420FrameReady(I420FRAMEREADY_CALLBACK callback)300 void SimplePeerConnection::RegisterOnRemoteI420FrameReady(
301     I420FRAMEREADY_CALLBACK callback) {
302   if (remote_video_observer_)
303     remote_video_observer_->SetVideoCallback(callback);
304 }
305 
RegisterOnLocalDataChannelReady(LOCALDATACHANNELREADY_CALLBACK callback)306 void SimplePeerConnection::RegisterOnLocalDataChannelReady(
307     LOCALDATACHANNELREADY_CALLBACK callback) {
308   OnLocalDataChannelReady = callback;
309 }
310 
RegisterOnDataFromDataChannelReady(DATAFROMEDATECHANNELREADY_CALLBACK callback)311 void SimplePeerConnection::RegisterOnDataFromDataChannelReady(
312     DATAFROMEDATECHANNELREADY_CALLBACK callback) {
313   OnDataFromDataChannelReady = callback;
314 }
315 
RegisterOnFailure(FAILURE_CALLBACK callback)316 void SimplePeerConnection::RegisterOnFailure(FAILURE_CALLBACK callback) {
317   OnFailureMessage = callback;
318 }
319 
RegisterOnAudioBusReady(AUDIOBUSREADY_CALLBACK callback)320 void SimplePeerConnection::RegisterOnAudioBusReady(
321     AUDIOBUSREADY_CALLBACK callback) {
322   OnAudioReady = callback;
323 }
324 
RegisterOnLocalSdpReadytoSend(LOCALSDPREADYTOSEND_CALLBACK callback)325 void SimplePeerConnection::RegisterOnLocalSdpReadytoSend(
326     LOCALSDPREADYTOSEND_CALLBACK callback) {
327   OnLocalSdpReady = callback;
328 }
329 
RegisterOnIceCandidateReadytoSend(ICECANDIDATEREADYTOSEND_CALLBACK callback)330 void SimplePeerConnection::RegisterOnIceCandidateReadytoSend(
331     ICECANDIDATEREADYTOSEND_CALLBACK callback) {
332   OnIceCandidateReady = callback;
333 }
334 
SetRemoteDescription(const char * type,const char * sdp)335 bool SimplePeerConnection::SetRemoteDescription(const char* type,
336                                                 const char* sdp) {
337   if (!peer_connection_)
338     return false;
339 
340   std::string remote_desc(sdp);
341   std::string desc_type(type);
342   webrtc::SdpParseError error;
343   webrtc::SessionDescriptionInterface* session_description(
344       webrtc::CreateSessionDescription(desc_type, remote_desc, &error));
345   if (!session_description) {
346     RTC_LOG(LS_WARNING) << "Can't parse received session description message. "
347                            "SdpParseError was: "
348                         << error.description;
349     return false;
350   }
351   RTC_LOG(LS_INFO) << " Received session description :" << remote_desc;
352   peer_connection_->SetRemoteDescription(
353       DummySetSessionDescriptionObserver::Create().get(), session_description);
354 
355   return true;
356 }
357 
AddIceCandidate(const char * candidate,const int sdp_mlineindex,const char * sdp_mid)358 bool SimplePeerConnection::AddIceCandidate(const char* candidate,
359                                            const int sdp_mlineindex,
360                                            const char* sdp_mid) {
361   if (!peer_connection_)
362     return false;
363 
364   webrtc::SdpParseError error;
365   std::unique_ptr<webrtc::IceCandidateInterface> ice_candidate(
366       webrtc::CreateIceCandidate(sdp_mid, sdp_mlineindex, candidate, &error));
367   if (!ice_candidate.get()) {
368     RTC_LOG(LS_WARNING) << "Can't parse received candidate message. "
369                            "SdpParseError was: "
370                         << error.description;
371     return false;
372   }
373   if (!peer_connection_->AddIceCandidate(ice_candidate.get())) {
374     RTC_LOG(LS_WARNING) << "Failed to apply the received candidate";
375     return false;
376   }
377   RTC_LOG(LS_INFO) << " Received candidate :" << candidate;
378   return true;
379 }
380 
SetAudioControl(bool is_mute,bool is_record)381 void SimplePeerConnection::SetAudioControl(bool is_mute, bool is_record) {
382   is_mute_audio_ = is_mute;
383   is_record_audio_ = is_record;
384 
385   SetAudioControl();
386 }
387 
SetAudioControl()388 void SimplePeerConnection::SetAudioControl() {
389   if (!remote_stream_)
390     return;
391   webrtc::AudioTrackVector tracks = remote_stream_->GetAudioTracks();
392   if (tracks.empty())
393     return;
394 
395   rtc::scoped_refptr<webrtc::AudioTrackInterface>& audio_track = tracks[0];
396   if (is_record_audio_)
397     audio_track->AddSink(this);
398   else
399     audio_track->RemoveSink(this);
400 
401   for (auto& track : tracks) {
402     if (is_mute_audio_)
403       track->set_enabled(false);
404     else
405       track->set_enabled(true);
406   }
407 }
408 
OnAddStream(rtc::scoped_refptr<webrtc::MediaStreamInterface> stream)409 void SimplePeerConnection::OnAddStream(
410     rtc::scoped_refptr<webrtc::MediaStreamInterface> stream) {
411   RTC_LOG(LS_INFO) << __FUNCTION__ << " " << stream->id();
412   remote_stream_ = stream;
413   if (remote_video_observer_ && !remote_stream_->GetVideoTracks().empty()) {
414     remote_stream_->GetVideoTracks()[0]->AddOrUpdateSink(
415         remote_video_observer_.get(), rtc::VideoSinkWants());
416   }
417   SetAudioControl();
418 }
419 
AddStreams(bool audio_only)420 void SimplePeerConnection::AddStreams(bool audio_only) {
421   if (active_streams_.find(kStreamId) != active_streams_.end())
422     return;  // Already added.
423 
424   rtc::scoped_refptr<webrtc::MediaStreamInterface> stream =
425       g_peer_connection_factory->CreateLocalMediaStream(kStreamId);
426 
427   rtc::scoped_refptr<webrtc::AudioTrackInterface> audio_track(
428       g_peer_connection_factory->CreateAudioTrack(
429           kAudioLabel,
430           g_peer_connection_factory->CreateAudioSource(cricket::AudioOptions())
431               .get()));
432   stream->AddTrack(audio_track);
433 
434   if (!audio_only) {
435 #if defined(WEBRTC_ANDROID)
436     JNIEnv* env = webrtc::jni::GetEnv();
437     jclass pc_factory_class =
438         unity_plugin::FindClass(env, "org/webrtc/UnityUtility");
439     jmethodID load_texture_helper_method = webrtc::GetStaticMethodID(
440         env, pc_factory_class, "LoadSurfaceTextureHelper",
441         "()Lorg/webrtc/SurfaceTextureHelper;");
442     jobject texture_helper = env->CallStaticObjectMethod(
443         pc_factory_class, load_texture_helper_method);
444     CHECK_EXCEPTION(env);
445     RTC_DCHECK(texture_helper != nullptr)
446         << "Cannot get the Surface Texture Helper.";
447 
448     auto source = rtc::make_ref_counted<webrtc::jni::AndroidVideoTrackSource>(
449         g_signaling_thread.get(), env, /*is_screencast=*/false,
450         /*align_timestamps=*/true);
451 
452     // link with VideoCapturer (Camera);
453     jmethodID link_camera_method = webrtc::GetStaticMethodID(
454         env, pc_factory_class, "LinkCamera",
455         "(JLorg/webrtc/SurfaceTextureHelper;)Lorg/webrtc/VideoCapturer;");
456     jobject camera_tmp =
457         env->CallStaticObjectMethod(pc_factory_class, link_camera_method,
458                                     (jlong)source.get(), texture_helper);
459     CHECK_EXCEPTION(env);
460     g_camera = (jobject)env->NewGlobalRef(camera_tmp);
461 
462     rtc::scoped_refptr<webrtc::VideoTrackInterface> video_track(
463         g_peer_connection_factory->CreateVideoTrack(kVideoLabel,
464                                                     source.release()));
465     stream->AddTrack(video_track);
466 #else
467     rtc::scoped_refptr<CapturerTrackSource> video_device =
468         CapturerTrackSource::Create();
469     if (video_device) {
470       rtc::scoped_refptr<webrtc::VideoTrackInterface> video_track(
471           g_peer_connection_factory->CreateVideoTrack(kVideoLabel,
472                                                       video_device.get()));
473 
474       stream->AddTrack(video_track);
475     }
476 #endif
477     if (local_video_observer_ && !stream->GetVideoTracks().empty()) {
478       stream->GetVideoTracks()[0]->AddOrUpdateSink(local_video_observer_.get(),
479                                                    rtc::VideoSinkWants());
480     }
481   }
482 
483   if (!peer_connection_->AddStream(stream.get())) {
484     RTC_LOG(LS_ERROR) << "Adding stream to PeerConnection failed";
485   }
486 
487   typedef std::pair<std::string,
488                     rtc::scoped_refptr<webrtc::MediaStreamInterface>>
489       MediaStreamPair;
490   active_streams_.insert(MediaStreamPair(stream->id(), stream));
491 }
492 
CreateDataChannel()493 bool SimplePeerConnection::CreateDataChannel() {
494   struct webrtc::DataChannelInit init;
495   init.ordered = true;
496   init.reliable = true;
497   auto result = peer_connection_->CreateDataChannelOrError("Hello", &init);
498   if (result.ok()) {
499     data_channel_ = result.MoveValue();
500     data_channel_->RegisterObserver(this);
501     RTC_LOG(LS_INFO) << "Succeeds to create data channel";
502     return true;
503   } else {
504     RTC_LOG(LS_INFO) << "Fails to create data channel";
505     return false;
506   }
507 }
508 
CloseDataChannel()509 void SimplePeerConnection::CloseDataChannel() {
510   if (data_channel_.get()) {
511     data_channel_->UnregisterObserver();
512     data_channel_->Close();
513   }
514   data_channel_ = nullptr;
515 }
516 
SendDataViaDataChannel(const std::string & data)517 bool SimplePeerConnection::SendDataViaDataChannel(const std::string& data) {
518   if (!data_channel_.get()) {
519     RTC_LOG(LS_INFO) << "Data channel is not established";
520     return false;
521   }
522   webrtc::DataBuffer buffer(data);
523   data_channel_->Send(buffer);
524   return true;
525 }
526 
527 // Peerconnection observer
OnDataChannel(rtc::scoped_refptr<webrtc::DataChannelInterface> channel)528 void SimplePeerConnection::OnDataChannel(
529     rtc::scoped_refptr<webrtc::DataChannelInterface> channel) {
530   channel->RegisterObserver(this);
531 }
532 
OnStateChange()533 void SimplePeerConnection::OnStateChange() {
534   if (data_channel_) {
535     webrtc::DataChannelInterface::DataState state = data_channel_->state();
536     if (state == webrtc::DataChannelInterface::kOpen) {
537       if (OnLocalDataChannelReady)
538         OnLocalDataChannelReady();
539       RTC_LOG(LS_INFO) << "Data channel is open";
540     }
541   }
542 }
543 
544 //  A data buffer was successfully received.
OnMessage(const webrtc::DataBuffer & buffer)545 void SimplePeerConnection::OnMessage(const webrtc::DataBuffer& buffer) {
546   size_t size = buffer.data.size();
547   char* msg = new char[size + 1];
548   memcpy(msg, buffer.data.data(), size);
549   msg[size] = 0;
550   if (OnDataFromDataChannelReady)
551     OnDataFromDataChannelReady(msg);
552   delete[] msg;
553 }
554 
555 // AudioTrackSinkInterface implementation.
OnData(const void * audio_data,int bits_per_sample,int sample_rate,size_t number_of_channels,size_t number_of_frames)556 void SimplePeerConnection::OnData(const void* audio_data,
557                                   int bits_per_sample,
558                                   int sample_rate,
559                                   size_t number_of_channels,
560                                   size_t number_of_frames) {
561   if (OnAudioReady)
562     OnAudioReady(audio_data, bits_per_sample, sample_rate,
563                  static_cast<int>(number_of_channels),
564                  static_cast<int>(number_of_frames));
565 }
566 
GetRemoteAudioTrackSsrcs()567 std::vector<uint32_t> SimplePeerConnection::GetRemoteAudioTrackSsrcs() {
568   std::vector<rtc::scoped_refptr<webrtc::RtpReceiverInterface>> receivers =
569       peer_connection_->GetReceivers();
570 
571   std::vector<uint32_t> ssrcs;
572   for (const auto& receiver : receivers) {
573     if (receiver->media_type() != cricket::MEDIA_TYPE_AUDIO)
574       continue;
575 
576     std::vector<webrtc::RtpEncodingParameters> params =
577         receiver->GetParameters().encodings;
578 
579     for (const auto& param : params) {
580       uint32_t ssrc = param.ssrc.value_or(0);
581       if (ssrc > 0)
582         ssrcs.push_back(ssrc);
583     }
584   }
585 
586   return ssrcs;
587 }
588