webrtc-m79-外部解码器的注册

bool WebRtcVideoChannel::SetRecvParameters(const VideoRecvParameters& params) {
  RTC_DCHECK_RUN_ON(&thread_checker_);
  TRACE_EVENT0("webrtc", "WebRtcVideoChannel::SetRecvParameters");
  RTC_LOG(LS_INFO) << "SetRecvParameters: " << params.ToString();
  ChangedRecvParameters changed_params;
  if (!GetChangedRecvParameters(params, &changed_params)) {
    return false;
  }
  if (changed_params.flexfec_payload_type) {
    RTC_LOG(LS_INFO) << "Changing FlexFEC payload type (recv) from "
                     << recv_flexfec_payload_type_ << " to "
                     << *changed_params.flexfec_payload_type;
    recv_flexfec_payload_type_ = *changed_params.flexfec_payload_type;
  }
  if (changed_params.rtp_header_extensions) {
    recv_rtp_extensions_ = *changed_params.rtp_header_extensions;
  }
  if (changed_params.codec_settings) {
    RTC_LOG(LS_INFO) << "Changing recv codecs from "
                     << CodecSettingsVectorToString(recv_codecs_) << " to "
                     << CodecSettingsVectorToString(
                            *changed_params.codec_settings);
    recv_codecs_ = *changed_params.codec_settings; //////////////////std::vector<VideoCodecSettings> recv_codecs_
  }

  for (auto& kv : receive_streams_) {
    kv.second->SetRecvParameters(changed_params);
  }
  recv_params_ = params;
  return true;
}


bool WebRtcVideoChannel::AddRecvStream(const StreamParams& sp,
                                       bool default_stream) {
  RTC_DCHECK_RUN_ON(&thread_checker_);

  RTC_LOG(LS_INFO) << "AddRecvStream"
                   << (default_stream ? " (default stream)" : "") << ": "
                   << sp.ToString();
  if (!sp.has_ssrcs()) {
    // This is a StreamParam with unsignaled SSRCs. Store it, so it can be used
    // later when we know the SSRC on the first packet arrival.
    unsignaled_stream_params_ = sp;
    return true;
  }

  if (!ValidateStreamParams(sp))
    return false;

  uint32_t ssrc = sp.first_ssrc();

  // Remove running stream if this was a default stream.
  const auto& prev_stream = receive_streams_.find(ssrc);
  if (prev_stream != receive_streams_.end()) {
    if (default_stream || !prev_stream->second->IsDefaultStream()) {
      RTC_LOG(LS_ERROR) << "Receive stream for SSRC '" << ssrc
                        << "' already exists.";
      return false;
    }
    DeleteReceiveStream(prev_stream->second);
    receive_streams_.erase(prev_stream);
  }

  if (!ValidateReceiveSsrcAvailability(sp))
    return false;

  for (uint32_t used_ssrc : sp.ssrcs)
    receive_ssrcs_.insert(used_ssrc);

  webrtc::VideoReceiveStream::Config config(this, media_transport_config());
  webrtc::FlexfecReceiveStream::Config flexfec_config(this);
  ConfigureReceiverRtp(&config, &flexfec_config, sp);

  config.crypto_options = crypto_options_;
  config.enable_prerenderer_smoothing =
      video_config_.enable_prerenderer_smoothing;
  if (!sp.stream_ids().empty()) {
    config.sync_group = sp.stream_ids()[0];
  }

  receive_streams_[ssrc] = new WebRtcVideoReceiveStream( //注意这里
      this, call_, sp, std::move(config), decoder_factory_, default_stream,
      recv_codecs_, flexfec_config);

  return true;
}


WebRtcVideoChannel::WebRtcVideoReceiveStream::WebRtcVideoReceiveStream(
    WebRtcVideoChannel* channel,
    webrtc::Call* call,
    const StreamParams& sp,
    webrtc::VideoReceiveStream::Config config,
    webrtc::VideoDecoderFactory* decoder_factory,
    bool default_stream,
    const std::vector<VideoCodecSettings>& recv_codecs, //注意这里
    const webrtc::FlexfecReceiveStream::Config& flexfec_config)
    : channel_(channel),
      call_(call),
      stream_params_(sp),
      stream_(NULL),
      default_stream_(default_stream),
      config_(std::move(config)),
      flexfec_config_(flexfec_config),
      flexfec_stream_(nullptr),
      decoder_factory_(decoder_factory),
      sink_(NULL),
      first_frame_timestamp_(-1),
      estimated_remote_start_ntp_time_ms_(0) {
  config_.renderer = this;  
  ConfigureCodecs(recv_codecs); //注意这里
  ConfigureFlexfecCodec(flexfec_config.payload_type);
  MaybeRecreateWebRtcFlexfecStream();
  RecreateWebRtcVideoStream(); 
}



void WebRtcVideoChannel::WebRtcVideoReceiveStream::ConfigureCodecs(
    const std::vector<VideoCodecSettings>& recv_codecs) {
  RTC_DCHECK(!recv_codecs.empty());
  config_.decoders.clear();
  config_.rtp.rtx_associated_payload_types.clear();
  config_.rtp.raw_payload_types.clear();
  for (const auto& recv_codec : recv_codecs) {
    webrtc::SdpVideoFormat video_format(recv_codec.codec.name,
                                        recv_codec.codec.params);

    webrtc::VideoReceiveStream::Decoder decoder;
    decoder.decoder_factory = decoder_factory_; // decoder_factory_ 就是 webrtc::CreateBuiltinVideoDecoderFactory() 返回值，也就是 InternalDecoderFactory
    decoder.video_format = video_format;
    decoder.payload_type = recv_codec.codec.id;
    decoder.video_format =
        webrtc::SdpVideoFormat(recv_codec.codec.name, recv_codec.codec.params);
    config_.decoders.push_back(decoder); //注意这里
    config_.rtp.rtx_associated_payload_types[recv_codec.rtx_payload_type] =
        recv_codec.codec.id;
    if (recv_codec.codec.packetization == kPacketizationParamRaw) {
      config_.rtp.raw_payload_types.insert(recv_codec.codec.id);
    }
  }

  const auto& codec = recv_codecs.front();
  config_.rtp.ulpfec_payload_type = codec.ulpfec.ulpfec_payload_type;
  config_.rtp.red_payload_type = codec.ulpfec.red_payload_type;

  config_.rtp.lntf.enabled = HasLntf(codec.codec);
  config_.rtp.nack.rtp_history_ms = HasNack(codec.codec) ? kNackHistoryMs : 0;
  config_.rtp.rtcp_xr.receiver_reference_time_report = HasRrtr(codec.codec);
  if (codec.ulpfec.red_rtx_payload_type != -1) {
    config_.rtp
        .rtx_associated_payload_types[codec.ulpfec.red_rtx_payload_type] =
        codec.ulpfec.red_payload_type;
  }
}



void VideoReceiveStream::Start()
===>
    std::unique_ptr<VideoDecoder> video_decoder =
        decoder.decoder_factory->LegacyCreateVideoDecoder(decoder.video_format, //就是 VideoDecoderFactory::LegacyCreateVideoDecoder 
                                                          config_.stream_id);

    video_receiver_.RegisterExternalDecoder(video_decoders_.back().get(),
                                            decoder.payload_type);



std::unique_ptr<VideoDecoder> VideoDecoderFactory::LegacyCreateVideoDecoder(
    const SdpVideoFormat& format,
    const std::string& receive_stream_id) {
  return CreateVideoDecoder(format); // 多态
}

std::unique_ptr<VideoDecoder> InternalDecoderFactory::CreateVideoDecoder(
    const SdpVideoFormat& format) {
  if (!IsFormatSupported(GetSupportedFormats(), format)) {
    RTC_LOG(LS_ERROR) << "Trying to create decoder for unsupported format";
    return nullptr;
  }

  if (absl::EqualsIgnoreCase(format.name, cricket::kVp8CodecName))
    return VP8Decoder::Create(); //
  if (absl::EqualsIgnoreCase(format.name, cricket::kVp9CodecName))
    return VP9Decoder::Create(); //
  if (absl::EqualsIgnoreCase(format.name, cricket::kH264CodecName))
    return H264Decoder::Create(); //

  RTC_NOTREACHED();
  return nullptr;
}



void VideoReceiver2::RegisterExternalDecoder(VideoDecoder* externalDecoder,
                                             uint8_t payloadType) {
  RTC_DCHECK_RUN_ON(&construction_thread_checker_);
  RTC_DCHECK(!IsDecoderThreadRunning());
  if (externalDecoder == nullptr) {
    RTC_CHECK(codecDataBase_.DeregisterExternalDecoder(payloadType));
    return;
  }
  codecDataBase_.RegisterExternalDecoder(externalDecoder, payloadType);
}