feat(cmd): implemented multicast audio publishing

Author: Hamdan Anwar Sayeed

README.md

@@ -151,6 +151,20 @@ lk room join --identity bot \
   <room_name>
 ```
 
+### Publish audio from UDP Multicast
+
+It's possible to publish audio in the Opus codec from a multicast packet stream over a UDP socket. `lk` can act as a multicast listener and publish receiving audio packets. For example, if you want to publish audio packets that are being sent to multicast address `225.8.11.101` and port `9001` on a network connection `en0`,
+
+Run `lk` like this:
+
+```shell
+lk room join --identity bot \
+  --publish-multicast \
+  --multicast-endpoint 225.8.11.101:9001 \
+  --multicast-network-name en0 \
+  <room_name>
+```
+
 ### Publish streams from your application
 
 Using unix sockets, it's also possible to publish streams from your application. The tracks need to be encoded into

cmd/lk/join.go

@@ -28,6 +28,7 @@ import (
 
 	"github.com/pion/rtcp"
 	"github.com/pion/webrtc/v3"
+	"github.com/pion/webrtc/v3/pkg/media"
 	"github.com/urfave/cli/v3"
 
 	provider2 "github.com/livekit/livekit-cli/pkg/provider"
@@ -270,6 +271,57 @@ func publishFile(room *lksdk.Room,
 	return err
 }
 
+func publishMulticast(room *lksdk.Room,
+	multicastEndpoint string,
+	networkName string,
+	packetDuration int64,
+) error {
+	track, err := lksdk.NewLocalTrack(webrtc.RTPCodecCapability{MimeType: webrtc.MimeTypeOpus})
+	if err != nil {
+		return err
+	}
+
+	_, err = room.LocalParticipant.PublishTrack(track, &lksdk.TrackPublicationOptions{
+		Source: livekit.TrackSource_MICROPHONE,
+	})
+	if err != nil {
+		return err
+	}
+
+	addr, err := net.ResolveUDPAddr("udp4", multicastEndpoint)
+	if err != nil {
+		return err
+	}
+	iface, err := net.InterfaceByName(networkName)
+	if err != nil {
+		return err
+	}
+
+	conn, err := net.ListenMulticastUDP("udp4", iface, addr)
+	if err != nil {
+		return err
+	}
+	go publishMulticastPackets(conn, track, packetDuration)
+	return nil
+}
+
+func publishMulticastPackets(conn *net.UDPConn,
+	track *lksdk.LocalTrack,
+	packetDuration int64,
+) {
+	buff := make([]byte, 1500)
+	for {
+		n, _, err := conn.ReadFromUDP(buff)
+		if err != nil {
+			logger.Errorw("Read from UDP error:", err)
+		}
+
+		if err = track.WriteSample(media.Sample{Data: buff[:n], Duration: time.Millisecond * time.Duration(packetDuration)}, &lksdk.SampleWriteOptions{}); err != nil {
+			logger.Errorw("Write sample error:", err)
+		}
+	}
+}
+
 func parseSocketFromName(name string) (string, string, string, error) {
 	// Extract mime type, socket type, and address
 	// e.g. h264://192.168.0.1:1234 (tcp)

cmd/lk/room.go

@@ -145,6 +145,10 @@ var (
 							Name:  "publish-demo",
 							Usage: "Publish demo video as a loop",
 						},
+						&cli.BoolFlag{
+							Name:  "publish-multicast",
+							Usage: "Publish multicast audio in Opus codec",
+						},
 						&cli.StringSliceFlag{
 							Name:      "publish",
 							TakesFile: true,
@@ -160,6 +164,19 @@ var (
 							Name:  "exit-after-publish",
 							Usage: "When publishing, exit after file or stream is complete",
 						},
+						&cli.StringFlag{
+							Name:  "multicast-endpoint",
+							Usage: "Multicast `ENDPOINT` to open the UDP socket. Should be of the format <MulticastIpAddress:MulticastPort>",
+						},
+						&cli.StringFlag{
+							Name:  "multicast-network-name",
+							Usage: "`NETWORK NAME` on which the UDP socket should be opened for multicast audio publishing",
+						},
+						&cli.IntFlag{
+							Name:  "multiast-packet-duration",
+							Usage: "Audio packet `DURATION` in milliseconds to be published from multicast",
+							Value: 20,
+						},
 					},
 				},
 				{
@@ -814,6 +831,21 @@ func joinRoom(ctx context.Context, cmd *cli.Command) error {
 
 	signal.Notify(done, syscall.SIGINT, syscall.SIGTERM, syscall.SIGQUIT)
 
+	if cmd.Bool("publish-multicast") {
+		multicastEndpoint := cmd.String("multicast-endpoint")
+		if multicastEndpoint == "" {
+			return fmt.Errorf("no multicast endpoint provided name provided")
+		}
+		networkName := cmd.String("network-name")
+		if networkName == "" {
+			return fmt.Errorf("no network name provided")
+		}
+		packetDuration := cmd.Int("packet-duration")
+		if err = publishMulticast(room, multicastEndpoint, networkName, packetDuration); err != nil {
+			return err
+		}
+	}
+
 	if cmd.Bool("publish-demo") {
 		if err = publishDemo(room); err != nil {
 			return err