Delphi WebRTC：在两个应用之间传输音频、视频与数据

  App A                                App B
    |                                    |
    |---- offer / answer / candidate --->|   your signalling
    |<-------- (WebSocket relay) --------|   server, text only
    |                                    |
    |---> "what is my public address?"   |   STUN, once per
    |     (STUN binding request)         |   candidate
    |                                    |
    |====== audio, video and data ======>|   direct, encrypted,
    |<===================================|   no server involved
    |                                    |
    |== only when nothing direct works ==|   TURN relay,
    |    (relayed candidate pair)        |   your server

procedure TFormServer.Start;
begin
  FServer := TsgcWebSocketServer.Create(nil);
  FServer.Port := 5000;
  FServer.OnMessage := OnSignallingMessage;
  FServer.Active := True;
end;

procedure TFormServer.OnSignallingMessage(
  Connection: TsgcWSConnection; const Text: string);
begin
  // relay verbatim to the other peer. The server never
  // parses the SDP, so it never learns about codecs.
  FServer.Broadcast(Text, '', '', Connection.Guid);
end;

procedure TFormPeer.OnIceCandidate(Sender: TObject;
  const aCandidate, aSdpMid: string;
  aSdpMLineIndex: Integer);
var
  oJSON: TsgcJSON;
begin
  oJSON := TsgcJSON.Create(nil);
  try
    oJSON.AddPair('kind', 'candidate');
    oJSON.AddPair('candidate', aCandidate);
    oJSON.AddPair('sdpMid', aSdpMid);
    oJSON.AddPair('sdpMLineIndex', aSdpMLineIndex);
    FSignalling.WriteData(oJSON.Text);
  finally
    FreeAndNil(oJSON);
  end;
end;

procedure TFormPeer.OnConnectionStateChange(Sender: TObject;
  aState: TsgcRTCConnectionState);
begin
  // rtccsNew, rtccsGathering, rtccsConnecting, rtccsConnected,
  // rtccsDisconnected, rtccsFailed, rtccsClosed
  if aState = rtccsConnected then
    Log(FPeer.SelectedLocalCandidate + ' -> ' +
        FPeer.SelectedRemoteCandidate);
end;

procedure TFormPeer.StartCall;
begin
  FPeer.RTCOptions.DTLS := True;  // SRTP keys come from DTLS

  FAudioTrack := FPeer.AddTrack(rtctkAudio, cctAudioOpus);
  FVideoTrack := FPeer.AddTrack(rtctkVideo, cctVideoVP8);

  FCapture := sgcCreateAudioCapture;
  if Assigned(FCapture) then
  begin
    FCapture.OnAudioCapture := OnAudioCaptured;
    FCapture.Start;
    if not FCapture.Active then
      Log(FCapture.LastError);
  end;

  FRenderer := sgcCreateAudioRenderer;
  if Assigned(FRenderer) then
    FRenderer.Start;

  FPeer.CreateOffer;
end;

procedure TFormPeer.OnAudioCaptured(Sender: TObject;
  const aPCM: TBytes;
  aSampleRate, aChannels, aSamplesPerChannel: Integer);
begin
  if Assigned(FAudioTrack) then
    FAudioTrack.SendPCM(aPCM, aSamplesPerChannel);
end;

uses
  sgcP2P_MediaCapture_Win;   // MSWINDOWS only

procedure TFormPeer.StartCamera;
begin
  FVideoCapture := TsgcVideoCapture_Win.Create(640,
    480, 30);
  FVideoCapture.DeviceIndex := 0;
  FVideoCapture.OnVideoCapture := OnVideoCaptured;
  FVideoCapture.Start;
end;

procedure TFormPeer.OnVideoCaptured(Sender: TObject;
  const aFrame: TsgcVideoFrame);
begin
  if Assigned(FVideoTrack) then
    FVideoTrack.SendVideoFrame(aFrame);
end;