WebRTC代码流程
原文出处：初始化
new VoiceEngine/VoiceEngine_create
new VoiceEngineData
webrtc::VoiceEngine::Create
GetVoiceEngine
new VoiceEngineImpl
初始化SharedData
ProcessThread::CreateProcessThread
OutputMixer::Create
new OutputMixer
AudioConferenceMixer::Create
new AudioConferenceMixerImpl
AudioConferenceMixerImpl::Init
TransmitMixer::Create
new TransmitMixer
初始化VoEAudioProcessingImpl
初始化VoECodecImpl
初始化VoEDtmfImpl
初始化VoENetEqStatsImpl
初始化VoENetworkImpl
初始化VoERTP_RTCPImpl
初始化VoEVideoSyncImpl
初始化VoEVolumeControlImpl
初始化VoEBaseImpl
VoiceEngine_init
VoEBaseImpl::Init
WebRtcSpl_Init
ProcessThreadImpl::Start
AudioDeviceModuleImpl::Create
AudioDeviceModuleImpl::CreatePlatformSpecificObjects
new AudioDeviceTemplate
new AudioDeviceUtilityAndroid
SharedData::set_audio_device
ProcessThreadImpl::RegisterModule（AudioDeviceModuleImpl）
AudioDeviceModuleImpl::RegisterEventObserver
AudioDeviceModuleImpl::RegisterAudioCallback
AudioDeviceModuleImpl::init
AudioDeviceModuleImpl::SetPlayoutDevice
AudioDeviceModuleImpl::InitSpeaker
AudioDeviceModuleImpl::SetRecordingDevice
AudioDeviceModuleImpl::InitMicrophone
AudioDeviceModuleImpl::StereoPlayoutIsAvailable
AudioDeviceModuleImpl::SetStereoPlayout
AudioDeviceModuleImpl::SetStereoRecording
AudioProcessing::Create
new AudioProcessingImpl
new audioproc::Event
new EchoCancellationImpl
new EchoControlMobileImpl
new GainControlImpl
new HighPassFilterImpl
new LevelEstimatorImpl
new NoiseSuppressionImpl
new VoiceDetectionImpl
new GainControlForNewAgc
VoiceEngine_createChannel
VoEBaseImpl::CreateChannel
ChannelManager::CreateChannel
ChannelManager::CreateChannelInternal
Channel::CreateChannel
new Channel
VoEBaseImpl::InitializeChannel
Channel::SetEngineInformation
new VideoEngine
video_engine_jni.cc:VideoEngine_create
new VideoEngineData
vie(vie_imple.cc:webrtc::VideoEngine::Create())
new VideoEngineImpl
初始化ViEBaseImpl
new ViESharedData
初始化number_cores_（CpuInfo::DetectNumberOfCores(）
channel_manager_(new ViEChannelManager(0, number_cores_, config)),
input_manager_(new ViEInputManager(0, config)),
render_manager_(new ViERenderManager(0)),
module_process_thread_(ProcessThread::CreateProcessThread()),
new ProcessThreadImpl
channel_manager_/input_manager_使用module_process_thread_
module_process_thread_启动
VideoEngine_init
ViEBaseImpl::Init
VideoEngine_setVoiceEngine
ViEBaseImpl::SetVoiceEngine
ViEChannelManager::SetVoiceEngine
ViEChannel::SetVoiceChannel
ViESyncModule::ConfigureSync
new StreamSynchronization
new ViESyncDelay
VideoEngine_createChannel
VideoEngineData::CreateChannel
ViEBaseImpl::CreateChannel
ViEChannelManager::CreateChannel
new ChannelGroup
new VieRemb
BitrateController::CreateBitrateController
BitrateControllerImpl::BitrateControllerImpl
new CallStats
new EncoderStateFeedback
new WrappingBitrateEstimator
将主要Module注册到ProcessThread
new ViEEncoder
vcm_(*webrtc::VideoCodingModule::Create())
new VideoCodingModuleImpl
sender_(new vcm::VideoSender(clock, &post_encode_callback_)),
new DebugRecorder(媒体写文件)
receiver_(new vcm::VideoReceiver(clock, event_factory))
vpm_(*webrtc::VideoProcessingModule::Create(channel_id))),
new VideoProcessingModuleImpl
RtpRtcp::CreateRtpRtcp
new ModuleRtpRtcpImpl
RTPSender初始化
new RTPSenderVideo
RTCPSender初始化
RTCPReceiver初始化
RTCPReceiver::RegisterRtcpObservers
new ViEBitrateObserver
new ViEPacedSenderCallback
BitrateControllerImpl::CreateRtcpBandwidthObserver
ViEEncoder::Init
VideoCodingModuleImpl::InitializeSender
VideoSender::InitializeSender
VCMCodecDataBase::ResetSender
VideoProcessingModuleImpl::EnableTemporalDecimation
VPMFramePreprocessor::EnableTemporalDecimation
VPMVideoDecimator::EnableTemporalDecimation
VideoProcessingModuleImpl::EnableContentAnalysis
VPMFramePreprocessor::EnableContentAnalysis
new QMVideoSettingsCallback
VideoCodingModule::Codec
VCMCodecDataBase::Codec
VideoCodingModuleImpl::RegisterSendCodec
VideoSender::RegisterSendCodec
VCMCodecDataBase::SetSendCodec
CreateEncoder
VP8Encoder::Create
new VP8EncoderImpl
new VCMGenericEncoder
VCMGenericEncoder::InitEncode
VP8EncoderImpl::InitEncode
VCMGenericEncoder::RegisterEncodeCallback
VP8EncoderImpl::RegisterEncodeCompleteCallback
VCMGenericEncoder::SetPeriodicKeyFrames
ViEChannelManager::CreateChannelObject
new ViEChannel
ViEChannel::Init
VideoEngine_connectAudioChannel
ViEBaseImpl::ConnectAudioChannel
ViEChannelManager::ConnectVoiceChannel
ViEChannel::SetVoiceChannel
ProcessThreadImpl::RegisterModule(VoEVideoSync)
ViESyncModule::ConfigureSync
new StreamSynchronization
原文出处：发送Call
VoiceEngine_startListen
VoEBaseImpl::StartReceive
channelPtr->StartReceiving设置channel的receiving的状态
VoiceEngine_startPlayout
VoEBaseImpl::StartPlayout
VoEBaseImpl::StartPlayout--没有channelId，涉及到硬件，所以是唯一全局的
AudioDeviceModuleImpl::InitPlayout
AudioDeviceTemplate::InitPlayout
OpenSlesOutput::InitPlayout,设置状态
AudioDeviceModuleImpl::StartPlayout
AudioDeviceTemplate::StartPlayout
OpenSlesOutput::StartPlayout,创建硬件资源
Channel::StartPlayout
OutputMixer::SetMixabilityStatus
AudioConferenceMixerImpl::SetMixabilityStatus
AudioConferenceMixerImpl::AddParticipantToList加入到混音器中
VoiceEngine_startSend
VoEBaseImpl::StartSend
VoEBaseImpl::StartSend() --没有channelId，涉及到硬件，所以是唯一全局的
AudioDeviceModuleImpl::StartRecording
AudioDeviceTemplate::StartRecording
OpenSlesInput::StartRecording，创建硬件资源
AudioDeviceModuleImpl::InitRecording
AudioDeviceTemplate::InitRecording
OpenSlesInput::InitRecording，配置状态
Channel::StartSend，设置状态
VideoEngine_addRenderer
ViERenderImpl::AddRenderer
ViERenderManager::AddRenderStream
VideoRender::CreateVideoRender， VideoRender和上层的window一一对应
new ModuleVideoRenderImpl
new AndroidNativeOpenGl2Renderer
AndroidNativeOpenGl2Renderer::Init，和JNI环境关联起来
加入到render_list,??可以有多个Render吗？
ViERenderer::CreateViERenderer
new ViERenderer
new ViEExternalRendererImpl,用于回调
new VideoFrame
ViERenderer::Init
ModuleVideoRenderImpl::AddIncomingRenderStream
VideoRenderAndroid::AddIncomingRenderStream
AndroidNativeOpenGl2Renderer::CreateAndroidRenderChannel
new AndroidNativeOpenGl2Channel
AndroidNativeOpenGl2Channel::Init，
和JINI环境关联起来
注册两个Native函数，AndroidNativeOpenGl2Channel::DrawNativeStatic，AndroidNativeOpenGl2Channel::CreateOpenGLNativeStatic
streamId和AndroidStream（AndroidNativeOpenGl2Channel）一一对应，可以保存多个
new IncomingVideoStream
new VideoRenderFrames
IncomingVideoStream::SetRenderCallback初始化回调函数（AndroidNativeOpenGl2Channel）
IncomingVideoStream加入map中？？可以有多个？
VideoEngine_startRender
ViERenderer::StartRender
ModuleVideoRenderImpl::StartRender
IncomingVideoStream::Start
ThreadWrapper::CreateThread，回调是IncomingVideoStream::IncomingVideoStreamProcess
Thread启动
EventPosix::StartTimer
VideoRenderAndroid::StartRender
ThreadWrapper::CreateThread，回调是VideoRenderAndroid::JavaRenderThreadProcess
启动线程
VideoEngine_startReceive
ViEBaseImpl::StartReceive
ViEChannel::StartReceive
ViEReceiver::StartReceive,设置状态
VideoEngine_getCaptureDevice
ViECaptureImpl::GetCaptureDevice
ViEInputManager::GetDeviceName
VideoCaptureFactory::CreateDeviceInfo
new videocapturemodule::DeviceInfoAndroid
DeviceInfoAndroid::GetDeviceName
VideoEngine_allocateCaptureDevice
ViECaptureImpl::AllocateCaptureDevice
ViEInputManager::CreateCaptureDevice
ViECapturer::CreateViECapture
new ViECapturer
ThreadWrapper::CreateThread,回调函数ViECapturer::ViECaptureProcess
new OveruseFrameDetector
ViECapturer::Init
VideoCaptureFactory::Create
VideoCaptureImpl::Create
new videocapturemodule::VideoCaptureAndroid
VideoCaptureAndroid::RegisterCaptureDataCallback注册回调函数ViECapturer
在线程中注册Module，videocapturemodule::VideoCaptureAndroid
保存ID，可以有多个ViECapturer
VideoEngine_connectCaptureDevice
ViECaptureImpl::ConnectCaptureDevice,链接摄像头和channle
ViEFrameProviderBase::RegisterFrameCallback，可以有多个callback
ViECapturer::FrameCallbackChanged，将ViEEncoder作为回调类放到VieCapturer的回调list中
VideoCaptureAndroid::CaptureSettings
VideoCaptureAndroid::StopCapture
VideoCaptureAndroid::StartCapture，配置JNI环境，获取摄像头参数
VideoEngine_startCapture
ViECaptureImpl::StartCapture
ViECapturer::Start
ViEFrameProviderBase::GetBestFormat获取最好的尺寸
ViEEncoder::GetPreferedFrameSettings
VideoCaptureAndroid::StartCapture，配置JNI环境，获取摄像头参数
VideoEngine_startSend
ViEBaseImpl::StartSend
ViEEncoder::Pause，设置状态
ViEChannel::StartSend
ModuleRtpRtcpImpl::SetSendingMediaStatus
RTPSender::SetSendingMediaStatus设置状态为true
ModuleRtpRtcpImpl::SetSendingStatus
RTPSender::SetSendingStatus，初始化状态和RTP头
还能有多个ModuleRtpRtcpImpl？？？
ViEEncoder::SendKeyFrame
VideoCodingModuleImpl::IntraFrameRequest
VideoSender::IntraFrameRequest
VCMGenericEncoder::RequestFrame
VP8EncoderImpl::Encode
原文出处：音频接收流程
收到音频包
UdpSocketManagerPosixImpl::Run
UdpSocketManagerPosixImpl::Process
UdpSocketPosix::HasIncoming（recvfrom）
UdpTransportImpl::IncomingRTPCallback
UdpTransportImpl::IncomingRTPFunction
VoiceChannelTransport::IncomingRTPPacket
VoENetworkImpl::ReceivedRTPPacket
Channel::ReceivedRTPPacket
UpdatePlayoutTimestamp
AudioCodingModuleImpl::PlayoutTimestamp
AcmReceiver::GetPlayoutTimestamp
InitialDelayManager::GetPlayoutTimestamp
AudioDeviceModuleImpl::PlayoutDelay
AudioDeviceTemplate::PlayoutDelay
OpenSlesOutput::PlayoutDelay
Channel::IsPacketInOrder
ReceiveStatisticsImpl::GetStatistician (这个类应该管理所有的流)
StreamStatisticianImpl::IsPacketInOrder
StreamStatisticianImpl::InOrderPacketInternal （可以学习一下这个判断乱序代码）
Channel::IsPacketRetransmitted
StreamStatisticianImpl::IsRetransmitOfOldPacket （可以学习一下这个判断重传代码）
ReceiveStatisticsImpl::IncomingPacket
如果是第一次收到，创建StreamStatisticianImpl
StreamStatisticianImpl::IncomingPacket
StreamStatisticianImpl::UpdateCounters 记录必要的信息， 用于统计，如乱序、重传、jitbuff、计算bitrate
StreamStatisticianImpl::NotifyRtpCallback
ReceiveStatisticsImpl::DataCountersUpdated（没做处理）
Channel::ReceivePacket
RtpReceiverImpl::IncomingRtpPacket
check ssrc/play/timestamp
RtpReceiverImpl::CheckSSRCChanged
如果是第一次，则Channel::OnInitializeDecoder
AudioCodingModule::Codec， 选择具体的Codec Inst（数组，一开始已经初始化好所有的）
AudioCodingModuleImpl::RegisterReceiveCodec
AudioCodingModuleImpl::GetAudioDecoder
AudioCodingModuleImpl::CreateCodec
ACMCodecDB::CreateCodecInstance
new ACMISAC
AcmReceiver::AddCodec
NetEq初始化
NetEqImpl::RegisterExternalDecoder
RTPReceiverAudio::ParseRtpPacket
RTPReceiverAudio::ParseAudioCodecSpecific
判断是不是dtmf、cgn、2833等
Channel::OnReceivedPayloadData
AudioCodingModuleImpl::IncomingPacket
AcmReceiver::InsertPacket
ack
唇音同步
NetEqImpl::InsertPacket
NetEqImpl::InsertPacketInternal
ACMISAC::IncomingPacket
ACMISAC::UpdateDecoderSampFreq
WebRtcIsac_SetDecSampRate
DecoderInitUb
Channel::UpdatePacketDelay
Channel::GetPlayoutFrequency(
AudioCodingModuleImpl::PlayoutFrequency()
AudioTrackJni::PlayThreadProcess
AudioDeviceBuffer::RequestPlayoutData
VoEBaseImpl::NeedMorePlayData
VoEBaseImpl::GetPlayoutData
AudioConferenceMixerImpl::Process
AudioConferenceMixerImpl::UpdateToMix
所有的与会者Channel::GetAudioFrame
AudioCodingModuleImpl::PlayoutData10Ms
AcmReceiver::GetAudio
时间判断
可能产生静音包
NetEqImpl::GetAudio
NetEqImpl::GetAudioInternal
NetEqImpl::Decode
ACMISAC::DecodePlc
NetEqImpl::DecodeLoop
ACMISAC::Decode
NetEqImpl::DecodedRtpInfo
ack的处理
重采样
Channel::UpdateRxVadDetection
Channel::OnRxVadDetected
AudioProcessingImpl::ProcessStream
AudioBuffer::DeinterleaveFrom
AudioBuffer::InterleaveTo
必要的音频处理，scale之类的
音量判断
合成声音
OutputMixer::GetMixedAudio 获取合成完的数据
AudioDeviceBuffer::GetPlayoutData
复制到java内存
调用Java程序CallIntMethod(_javaScObj, _javaMidPlayAudio,
原文出处：音频发送流程
发送音频
OpenSlesInput::RecorderSimpleBufferQueueCallback
OpenSlesInput::RecorderSimpleBufferQueueCallbackHandler，保存数据
OpenSlesInput::CbThreadImpl
AudioDeviceBuffer::SetRecordedBuffer， 复制数据
AudioDeviceBuffer::SetVQEData
AudioDeviceBuffer::DeliverRecordedData
VoEBaseImpl::RecordedDataIsAvailable
VoEBaseImpl::ProcessRecordedDataWithAPM
AudioDeviceModuleImpl::MaxMicrophoneVolume
AudioDeviceTemplate::MaxMicrophoneVolume
TransmitMixer::PrepareDemux
TransmitMixer::GenerateAudioFrame
DownConvertToCodecFormat, 单双转换，重采样
PushResampler<T>::Resample
TransmitMixer::ProcessAudio，agc、aec、anc
AudioProcessingImpl::ProcessStream
AudioBuffer::DeinterleaveFrom
AudioProcessingImpl::ProcessStreamLocked
AudioBuffer::InterleaveTo
TransmitMixer::DemuxAndMix
Channel::Demultiplex 复制数据
Channel::PrepareEncodeAndSend， 一些处理，比如添加dtmf
TransmitMixer::EncodeAndSend()
Channel::EncodeAndSend
AudioCodingModuleImpl::Add10MsData
AudioCodingModuleImpl::PreprocessToAddData 存储数据
AudioCodingModuleImpl::Process
AudioCodingModuleImpl::ProcessSingleStream
ACMGenericCodec::Encode
ACMISAC::InternalEncode
Channel::SendData
ModuleRtpRtcpImpl::SendOutgoingData
RTPSender::SendOutgoingData
RTPSenderAudio::SendAudio
RTPSender::BuildRTPheader
RTPSender::CreateRtpHeader
RTPSender::SendToNetwork
统计
RTPSender::SendPacketToNetwork
Channel::SendPacket
UdpTransportImpl::SendPacket
原文出处：视频接受流程
收到视频包
UdpSocketManagerPosixImpl::Run
UdpSocketManagerPosixImpl::Process
UdpSocketPosix::HasIncoming（recvfrom）
UdpTransportImpl::IncomingRTPCallback
UdpTransportImpl::IncomingRTPFunction
VideoChannelTransport::IncomingRTPPacket
ViENetworkImpl::ReceivedRTPPacket
ViEChannel::ReceivedRTPPacket
ViEReceiver::ReceivedRTPPacket
ViEReceiver::InsertRTPPacket
如果配置了抓包， 可以RtpDumpImpl::DumpPacket
RtpHeaderParserImpl::Parse
RtpHeaderParser::Parse
ViEReceiver::ReceivePacket
RtpReceiverImpl::IncomingRtpPacket
ssrc、payroad等检查
RTPReceiverVideo::ParseRtpPacket
ViEReceiver::OnReceivedPayloadData
VideoCodingModuleImpl::IncomingPacket
VideoReceiver::IncomingPacket
VCMReceiver::InsertPacket
VCMJitterBuffer::InsertPacket
VCMJitterBuffer::GetFrame, 完整frame/未完整frame/空frame
VCMFrameBuffer::InsertPacket， 组桢
如果完成， 插入可解码桢队列（decodable_frames_）
ViEChannel::ChannelDecodeProcess
VideoCodingModuleImpl::Decode
VideoReceiver::Decode
VCMReceiver::FrameForDecoding
VCMJitterBuffer::NextCompleteTimestamp，还未到render时间， 则等待
VCMJitterBuffer::ExtractAndSetDecode， 取frame
如果需要，抓图片？（）
VideoReceiver::Decode
VCMGenericDecoder::Decode
VP8DecoderImpl::Decode
decode完成（VP8是同步的， 直接在Decode中调用）
VCMDecodedFrameCallback::Decoded
ViEChannel::FrameToRender
图片预处理
ViEFrameProviderBase::DeliverFrame
ViERenderer::DeliverFrame
IncomingVideoStream::RenderFrame, 复制frame，放入队列
IncomingVideoStream::IncomingVideoStreamThreadFun
IncomingVideoStream::IncomingVideoStreamProcess
AndroidNativeOpenGl2Channel::RenderFrame， 复制frame
VideoRenderAndroid::JavaRenderThreadProcess
AndroidNativeOpenGl2Channel::DeliverFrame
调用JAVA层函数
AndroidNativeOpenGl2Channel::DrawNativeStatic
VideoRenderOpenGles20::Render
原文出处：视频发送流程
JNI调用
ProvideCameraFrame
VideoCaptureAndroid::OnIncomingFrame
VideoCaptureImpl::IncomingFrame
申请内存，转换层I420
VideoCaptureImpl::DeliverCapturedFrame
计算时间戳
ViECapturer::OnIncomingCapturedFrame
OveruseFrameDetector::FrameCaptured
复制frame，为什么？？？
ViECapturer::ViECaptureProcess
ViECapturer::DeliverI420Frame
ViEFrameProviderBase::DeliverFrame
遍历所有注册的观察着
ViEEncoder::DeliverFrame
encode之前的预处理（回调处理）
VideoCodingModuleImpl::AddVideoFrame
VideoSender::AddVideoFrame
VCMGenericEncoder::Encode
VP8EncoderImpl::Encode
编码
VP8EncoderImpl::GetEncodedPartitions
EncodedImageCallbackWrapper::Encoded
VCMEncodedFrameCallback::Encoded
ViEEncoder::SendData
ModuleRtpRtcpImpl::SendOutgoingData
RTPSender::SendOutgoingData
RTPSenderVideo::SendVideo
RTPSenderVideo::Send
拆包，RTP组包
RTPSenderVideo::SendVideoPacket
RTPSender::SendToNetwork
FEC
原文出处：发送端Webrtc视频Pipeline
从摄像头捕获特定帧率和分辨率的原始[YUV/RGB or MGPEG==>YUV/RGB]视频帧
拥塞控制
发送端基于”Loss-based Controller”估算发送端带宽 As，接收端基于”Delay-based controller”估算发送端带宽 Ar，发送端取两者的最小值作为当前发送端目标带宽，作用于编码器、Pacer以及Padder/FEC。
SendSideCongestionController
1、OnTransportFeedback 2、Process 3、MaybeTriggerOnNetworkChanged
BitrateController
1、OnDelayBasedBweResult 2、OnReceivedEstimatedBitrate 3、GetNetworkParameters
SendSideBandwidthEstimation
综合发送端带宽估计和接收端带宽估计，得出当前发送端目标带宽。
1、UpdateDelayBasedEstimate 2、UpdateReceiverEstimate 3、UpdateEstimate 4、CapBitrateToThresholds
BitrateAllocator
OnNetworkChanged
接收SendSideCongestionController::MaybeTriggerOnNetworkChanged回调过来的带宽变化通知。
SendSideCongestionController::MaybeTriggerOnNetworkChanged
==> Call::OnNetworkChanged
==> Call::OnNetworkChanged
==> BitrateAllocator::OnNetworkChanged
==> VideoSendStreamImpl::OnBitrateUpdated
==> FecController::UpdateFecRates and CalculateOverheadRateBps and ==> VideoStreamEncoder::OnBitrateUpdated
==> VideoSender::SetChannelParameters
==> VCMGenericEncoder::SetEncoderParameters
==> VideoEncoder::SetRateAllocation of different video encoder implementation.
编码
Rtp打包过程，图片来源:WebRTC中RTP/RTCP协议实现分析
VideoStreamEncoder
1、SetSource 2、SetSink 3、ConfigureEncoder 4、OnFrame
接收采集端过来的视频帧。
5、EncodeVideoFrame 6、CropAndScaleFrom 7、OnBitrateUpdated
调用vcm::VideoSender::SetChannelParameters，将新的带宽码率设置给编码器实例。
EncodedImageCallback
编码器编码数据回调接口。
VCMEncodedFrameCallback
EncodedImageCallback的wrapper。
vcm::VideoSender
VideoStreamEncoder实现EncodedImageCallback接口，将raw video frame交给vcm::VideoSender去编码，然后从EncodedImageCallback回调接口接收视频编码器编码之后的压缩数据。
1、RegisterExternalEncoder
注册发送端编码器实例。
2、RegisterSendCodec
VideoCodec，用来选择发送端将要使用的视频编码器，参数包括：编码器类型[VP8,VP9,H264…]、rtp payload type、宽、高、起始码率、最大码率、最小码率、目标码率、最大帧率、最大量化参数、不同分辨率的码率个数等。
3、AddVideoFrame
4、SetChannelParameters
Update the channel parameters based on new rates and rtt. This will also cause an immediate call to VideoEncoder::SetRateAllocation.
VideoEncoder
视频编码器接口
1、InitEncode
2、RegisterEncodeCompleteCallback
3、Release
4、Encode
5、SetRateAllocation
VCMGenericEncoder
VideoEncoder的wrapper，确保对VideoEncoder各个api的调用是序列化的。
SetEncoderParameters
设置参数: target_bitrate，loss_rate，rtt，input_frame_rate。
VCMEncoderDataBase
视频编码器数据库，因为同一时刻只有一个编码器会被一个VideoSender使用，所以这个数据库其实只有一个视频编码器，使用RegisterExternalEncoder注册。
1、RegisterExternalEncoder 2、SetSendCodec 3、GetEncoder 4、MatchesCurrentResolution 5、DeregisterExternalEncoder
EncoderSink
继承EncodedImageCallback接口，接收编码后的压缩数据。
VideoSendStreamImpl
VideoSendStreamImpl实现EncoderSink接口，接收VideoStreamEncoder回调过来的编码器编码之后的压缩数据。
1、OnEncodedImage 2、OnBitrateUpdated
Implements BitrateAllocatorObserver，接收带宽变化通知，并设置到编码器VideoStreamEncoder。
PayloadRouter
PayloadRouter routes outgoing data to the correct sending RTP module, based on the simulcast layer in RTPVideoHeader.
1、OnEncodedImage
封包 + FEC + 丢包重传
RtpRtcp
1、SendOutgoingData 2、TimeToSendPacket 3、TimeToSendPadding 4、SendRTCP
ModuleRtpRtcpImpl
实现RtpRtcp接口。
1、SendOutgoingData
接收PayloadRouter过来的压缩数据，通过SendOutgoingData继续传递给RTPSender封包。
2、TimeToSendPacket
接收从PacedSender回调过来的数据包，通过TimeToSendPacket传递给RTPSender。
RTPSender
1、SendOutgoingData
处理ModuleRtpRtcpImpl传递过来的压缩数据。
2、TimeToSendPacket
3、SelectiveRetransmissions
4、OnReceivedNack
接收到接收端rtcp返回的Nack，调用ReSendPacket进行丢包重传。
5、ReSendPacket
在RtpPacketHistory中回溯rtt，查找丢掉的包是否落在这段时间范围内，否则放弃重传；然后检查重传是否会导致“overusing retransmission bitrate”，如果是，则放弃重传。
6、SendToNetwork
把报文存储到RTPPacketHistory结构中进行缓存。接下来如果开启PacedSending，则构造Packe发送到PacedSender进行排队，否则直接发送到网络层。
7、SendPacketToNetwork
将PaceSender回调过来的数据包，通过SendRtp传递给Transport。
RTPSenderVideo
1、SetFecParameters
2、SetSelectiveRetransmissions
3、SendVideo
RTPSenderVideo处理后，通过SendToNetwork回调给RTPSender，然后，RTPSender将包保存在RtpPacketHistory 中等待RtpPacketSender派发。
4、SendVideoPacketWithFlexfec
FEC protection.
PacedSender
继承RtpPacketSender，平滑数据包的发送，通过TimeToSendPacket回调将数据包传递给PacketSender。
1、SetEstimatedBitrate
接收SendSideCongestionController::MaybeTriggerOnNetworkChanged回调过来的带宽变化通知。
2、SetSendBitrateLimits
3、SendPacket
由于视频帧数据量大，且在I帧出现时存在非常大的波动梯度，如果大量的数据在瞬间全部发送到网络中，很容易导致网络的拥塞和抖动，造成延迟和丢包。PacedSender的目的就是平滑数据包的发送，使得发送端能够按照估算的发送端带宽码率平缓的发送媒体数据。
BitrateProber
根据发送码率和发送的数据量估算从当前发送结束到下一次开始发送PacedSender需要等待的时间
IntervalBudget
根据发送码率和等待间隔计算PacedSender本次剩余可发送的数据量，只有bytesremaining 大于0才允许发送。
PacketRouter
继承PacketSender，通过TimeToSendPacket回调将PacedSender回调过来的数据包传递给相应的ModuleRtpRtcpImpl。
发送
Transport
1、SendRtp
2、SendRtcp
reference
- WebRTC中RTP/RTCP协议实现分析
- Analysis and Design of the Google Congestion Control for Web Real-time Communication (WebRTC)
- Understanding the Dynamic Behaviour of the Google Congestion Control
- Experimental Investigation of the Google Congestion Control for Real-Time Flows
- HANDLING PACKET LOSS IN WEBRTC
- Understanding the Basis of the Kalman Filter Via a Simple and Intuitive Deriv ation
- What is RMCAT congestion control, and how will it affect WebRTC?