add missing check on strict encryption + UDP multicast

internal/conf/conf.go

@@ -270,7 +270,11 @@ func (conf *Conf) CheckAndFillMissing() error {
 
 	if conf.Encryption == EncryptionStrict {
 		if _, ok := conf.Protocols[Protocol(gortsplib.TransportUDP)]; ok {
-			return fmt.Errorf("strict encryption can't be used with the UDP transport")
+			return fmt.Errorf("strict encryption can't be used with the UDP transport protocol")
+		}
+
+		if _, ok := conf.Protocols[Protocol(gortsplib.TransportUDPMulticast)]; ok {
+			return fmt.Errorf("strict encryption can't be used with the UDP-multicast transport protocol")
 		}
 	}