Fix WebRTC active producer with backchannel

pkg/webrtc/client.go

@@ -8,13 +8,24 @@ import (
 
 func (c *Conn) CreateOffer(medias []*streamer.Media) (string, error) {
 	for _, media := range medias {
+		switch media.Direction {
+		case streamer.DirectionRecvonly:
 			if _, err := c.pc.AddTransceiverFromKind(
-			webrtc.NewRTPCodecType(media.Kind), webrtc.RTPTransceiverInit{
-				Direction: webrtc.NewRTPTransceiverDirection(media.Direction),
-			},
+				webrtc.NewRTPCodecType(media.Kind),
+				webrtc.RTPTransceiverInit{Direction: webrtc.RTPTransceiverDirectionRecvonly},
 			); err != nil {
 				return "", err
 			}
+		case streamer.DirectionSendonly:
+			if _, err := c.pc.AddTransceiverFromTrack(
+				NewTrack(media.Kind),
+				webrtc.RTPTransceiverInit{Direction: webrtc.RTPTransceiverDirectionSendonly},
+			); err != nil {
+				return "", err
+			}
+		case streamer.DirectionSendRecv:
+			panic("not implemented")
+		}
 	}
 
 	desc, err := c.pc.CreateOffer(nil)

pkg/webrtc/producer.go

@@ -23,6 +23,9 @@ func (c *Conn) GetTrack(media *streamer.Media, codec *streamer.Codec) *streamer.
 		track = streamer.NewTrack(media, codec)
 	} else {
 		track = c.getProducerSendTrack(media, codec)
+		if track == nil {
+			panic("getProducerSendTrack return nil track")
+		}
 	}
 
 	c.tracks = append(c.tracks, track)