fix crash.

Author: cloudwebrtc

examples/b2bua/b2bua/buffer/buffer.go

@@ -126,6 +126,10 @@ func (b *Buffer) Bind(params webrtc.RTPParameters, o Options) {
 	b.Lock()
 	defer b.Unlock()
 
+	if len(params.Codecs) == 0 {
+		return
+	}
+
 	codec := params.Codecs[0]
 	b.clockRate = codec.ClockRate
 	b.maxBitrate = o.MaxBitRate

examples/b2bua/b2bua/udp.go

@@ -188,7 +188,6 @@ func (c *UdpTansport) onRtpPacket(trackType TrackType, packet []byte, raddr net.
 			c.buff.Bind(webrtc.RTPParameters{}, buffer.Options{
 				MaxBitRate: 1500,
 			})
-
 			c.buff.OnFeedback(func(fb []rtcp.Packet) {})
 		}
 		c.bmu.Unlock()