Added examples/rtp-forwarder

Add new example that demonstrates how to take WebRTC to RTP.
Also provides instructions and pre-canned SDP so you can easily
playback in VLC and ffmpeg.

Resolves #1061

examples/rtp-forwarder/main.go

@@ -0,0 +1,170 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"time"
+
+	"github.com/pion/rtcp"
+	"github.com/pion/webrtc/v2"
+	"github.com/pion/webrtc/v2/examples/internal/signal"
+)
+
+type udpConn struct {
+	conn *net.UDPConn
+	port int
+}
+
+func main() {
+	// Create context
+	ctx, cancel := context.WithCancel(context.Background())
+
+	// Create a MediaEngine object to configure the supported codec
+	m := webrtc.MediaEngine{}
+
+	// Setup the codecs you want to use.
+	// We'll use a VP8 codec but you can also define your own
+	m.RegisterCodec(webrtc.NewRTPOpusCodec(webrtc.DefaultPayloadTypeOpus, 48000))
+	m.RegisterCodec(webrtc.NewRTPVP8Codec(webrtc.DefaultPayloadTypeVP8, 90000))
+
+	// Create the API object with the MediaEngine
+	api := webrtc.NewAPI(webrtc.WithMediaEngine(m))
+
+	// Everything below is the Pion WebRTC API! Thanks for using it ❤️.
+
+	// Prepare the configuration
+	config := webrtc.Configuration{
+		ICEServers: []webrtc.ICEServer{
+			{
+				URLs: []string{"stun:stun.l.google.com:19302"},
+			},
+		},
+	}
+
+	// Create a new RTCPeerConnection
+	peerConnection, err := api.NewPeerConnection(config)
+	if err != nil {
+		panic(err)
+	}
+
+	// Allow us to receive 1 audio track, and 1 video track
+	if _, err = peerConnection.AddTransceiver(webrtc.RTPCodecTypeAudio); err != nil {
+		panic(err)
+	} else if _, err = peerConnection.AddTransceiver(webrtc.RTPCodecTypeVideo); err != nil {
+		panic(err)
+	}
+
+	// Create a local addr
+	var laddr *net.UDPAddr
+	if laddr, err = net.ResolveUDPAddr("udp", "127.0.0.1:"); err != nil {
+		panic(err)
+	}
+
+	// Prepare udp conns
+	udpConns := map[string]*udpConn{
+		"audio": {port: 4000},
+		"video": {port: 4002},
+	}
+	for _, c := range udpConns {
+		// Create remote addr
+		var raddr *net.UDPAddr
+		if raddr, err = net.ResolveUDPAddr("udp", fmt.Sprintf("127.0.0.1:%d", c.port)); err != nil {
+			panic(err)
+		}
+
+		// Dial udp
+		if c.conn, err = net.DialUDP("udp", laddr, raddr); err != nil {
+			panic(err)
+		}
+		defer func(conn net.PacketConn) {
+			if closeErr := conn.Close(); closeErr != nil {
+				panic(closeErr)
+			}
+		}(c.conn)
+	}
+
+	// Set a handler for when a new remote track starts, this handler will forward data to
+	// our UDP listeners.
+	// In your application this is where you would handle/process audio/video
+	peerConnection.OnTrack(func(track *webrtc.Track, receiver *webrtc.RTPReceiver) {
+		// Retrieve udp connection
+		c, ok := udpConns[track.Kind().String()]
+		if !ok {
+			return
+		}
+
+		// Send a PLI on an interval so that the publisher is pushing a keyframe every rtcpPLIInterval
+		go func() {
+			ticker := time.NewTicker(time.Second * 2)
+			for range ticker.C {
+				if rtcpErr := peerConnection.WriteRTCP([]rtcp.Packet{&rtcp.PictureLossIndication{MediaSSRC: track.SSRC()}}); rtcpErr != nil {
+					fmt.Println(rtcpErr)
+				}
+			}
+		}()
+
+		b := make([]byte, 1500)
+		for {
+			// Read
+			n, readErr := track.Read(b)
+			if readErr != nil {
+				panic(readErr)
+			}
+
+			// Write
+			if _, err = c.conn.Write(b[:n]); err != nil {
+				// For this particular example, third party applications usually timeout after a short
+				// amount of time during which the user doesn't have enough time to provide the answer
+				// to the browser.
+				// That's why, for this particular example, the user first needs to provide the answer
+				// to the browser then open the third party application. Therefore we must not kill
+				// the forward on "connection refused" errors
+				if opError, ok := err.(*net.OpError); ok && opError.Err.Error() == "write: connection refused" {
+					continue
+				}
+				panic(err)
+			}
+		}
+	})
+
+	// Set the handler for ICE connection state
+	// This will notify you when the peer has connected/disconnected
+	peerConnection.OnICEConnectionStateChange(func(connectionState webrtc.ICEConnectionState) {
+		fmt.Printf("Connection State has changed %s \n", connectionState.String())
+
+		if connectionState == webrtc.ICEConnectionStateConnected {
+			fmt.Println("Ctrl+C the remote client to stop the demo")
+		} else if connectionState == webrtc.ICEConnectionStateFailed ||
+			connectionState == webrtc.ICEConnectionStateDisconnected {
+			fmt.Println("Done forwarding")
+			cancel()
+		}
+	})
+
+	// Wait for the offer to be pasted
+	offer := webrtc.SessionDescription{}
+	signal.Decode(signal.MustReadStdin(), &offer)
+
+	// Set the remote SessionDescription
+	if err = peerConnection.SetRemoteDescription(offer); err != nil {
+		panic(err)
+	}
+
+	// Create answer
+	answer, err := peerConnection.CreateAnswer(nil)
+	if err != nil {
+		panic(err)
+	}
+
+	// Sets the LocalDescription, and starts our UDP listeners
+	if err = peerConnection.SetLocalDescription(answer); err != nil {
+		panic(err)
+	}
+
+	// Output the answer in base64 so we can paste it in browser
+	fmt.Println(signal.Encode(answer))
+
+	// Wait for context to be done
+	<-ctx.Done()
+}