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1.simulcast+SVC打开 std::string str[] = {"low", "medium", "high"}; std::string msid[] = {"l", "m", "h"}; //double pri = 0.8; //添加初始化参数，在此处设置时域层数，push 几多webrtc::RtpEncodingParameters就是几多层simulcast webrtc::RtpTransceiverInit rtpTI; for (int i = 3; i >= 1; i--) { webrtc::RtpEncodingParameters videoEncoding; videoEncoding.rid = str[i-1]; //videoEncoding.max_bitrate_bps = 3 * i * 100 * 1000; //videoEncoding.bitrate_priority = pri; videoEncoding.num_temporal_layers = 3; rtpTI.send_encodings.push_back(videoEncoding); //pri -= 0.2; rtpTI.stream_ids.push_back(msid[i-1]); //这个是SDP中msid参数的名字 } //单层simulcast的时候设置时域层数 //rtpTI.stream_ids.push_back("cam"); //webrtc::RtpEncodingParameters videoEncoding; //videoEncoding.rid = str[2]; //videoEncoding.num_temporal_layers = 3; //rtpTI.send_encodings.push_back(videoEncoding); auto ret = peer_connection_->AddTransceiver(video_track_,rtpTI); //这个可以获取当前设置的参数 webrtc::RtpParameters para = peer_connection_->GetSenders()[1]->GetParameters(); 2.设置编码优先挨次（编码选择）

src/media/engine/internal_encoder_factory.cc

std::vector<SdpVideoFormat> InternalEncoderFactory::GetSupportedFormats() const { std::vector<SdpVideoFormat> supported_codecs; //for (const webrtc::SdpVideoFormat& format : webrtc::SupportedH264Codecs()) // supported_codecs.push_back(format); // for (const webrtc::SdpVideoFormat& format : webrtc::SupportedVP9Codecs()) // supported_codecs.push_back(format); supported_codecs.push_back(SdpVideoFormat(cricket::kVp8CodecName)); return supported_codecs; } 3.设置H264可通过AddTransceiver参数初始化撑持SVC

增加对H264的撑持：
src/media/engine/webrtc_video_engine.cc

bool IsTemporalLayersSupported(const std::string& codec_name) { return absl::EqualsIgnoreCase(codec_name, kVp8CodecName) || absl::EqualsIgnoreCase(codec_name, kVp9CodecName) || absl::EqualsIgnoreCase(codec_name, kH264CodecName); } 4.关于simulcast和svc的常量参数设置

src/api/video/video_codec_constans.h

enum : int { kMaxEncoderBuffers = 8 }; enum : int { kMaxSimulcastStreams = 3 }; enum : int { kMaxSpatialLayers = 5 }; enum : int { kMaxTemporalStreams = 4 }; 5.simulcast media_session.cc static bool AddStreamParams(){ ... //这是对应的流的信息 StreamParams stream_param = sender.rids.empty() ? // Signal SSRCs and legacy simulcast (if requested). //老版本planb. rids为空，使用num_simulcast_layer来创建，内部挪用GenerateSsrcs CreateStreamParamsForNewSenderWithSsrcs( sender, rtcp_cname, include_rtx_streams, include_flexfec_stream, ssrc_generator) : // Signal RIDs and spec-compliant simulcast (if requested). CreateStreamParamsForNewSenderWithRids(sender, rtcp_cname); ... }

AddTransceiver只能在webrtc::SdpSemantics::kUnifiedPlan模式下，，这个在CreatePeerConnection时设置进去，目前设置完simulcast参数后，数据未推上去，应该是处事端暂未撑持。

webrtc::SdpSemantics::kPlanB模式下对应的是AddTrack,但是设置simulcast层数是在CreateOffer设置进去，webrtc::PeerConnectionInterface::RTCOfferAnswerOptions.num_simulcast_layers,但是此时按照抓包和断点看到的是只有2层，RTCOfferAnswerOptions里面默认是两层。
注：webrtc会按照当前视频的辨别率，以及预设的常量来决定实际的simulcast层数，例如640x480-位于(960,540)和(640,320)，所以参数是设置为(640,320)，最多2层simulcast

void Conductor::ConnectToPeer(int peer_id) { //RTC_DCHECK(peer_id_ == -1); //RTC_DCHECK(peer_id != -1); if (peer_connection_.get()) { main_wnd_->MessageBox( "Error", "We only support connecting to one peer at a time", true); return; } if (InitializePeerConnection()) { webrtc::PeerConnectionInterface::RTCOfferAnswerOptions options = webrtc::PeerConnectionInterface::RTCOfferAnswerOptions(); options.num_simulcast_layers = 3; peer_id_ = peer_id; peer_connection_->CreateOffer( this, options); } else { main_wnd_->MessageBox("Error", "Failed to initialize PeerConnection", true); } }

src/media/engine/simulcast.cc

// These tables describe from which resolution we can use how many // simulcast layers at what bitrates (maximum, target, and minimum). // Important!! Keep this table from high resolution to low resolution. // clang-format off const SimulcastFormat kSimulcastFormats[] = { {1920, 1080, 3, 5000, 4000, 800}, {1280, 720, 3, 2500, 2500, 600}, {960, 540, 3, 1200, 1200, 350}, {640, 360, 2, 700, 500, 150}, {480, 270, 2, 450, 350, 150}, {320, 180, 1, 200, 150, 30}, {0, 0, 1, 200, 150, 30} }; FindSimulcastFormatIndex: { ... for (uint32_t i = 0; i < arraysize(kSimulcastFormats); ++i) { if (width * height >= kSimulcastFormats[i].width * kSimulcastFormats[i].height) { return i; } } ... } ReconfigureEncoder ↓ CreateEncoderStreams ↓ GetSimulcastConfig ↓ LimitSimulcastLayerCount ↓ FindSimulcastFormatIndex 6.simulcast码率设置