+ void start_audio_stream_if_open ();
+
+#if (RTAUDIO_VERSION_MAJOR >= 6)
+ void rtaudio_error_callback(std::string const& error);
+ mutable boost::mutex _last_rtaudio_error_mutex;
+ std::string _last_rtaudio_error;
+ std::string last_rtaudio_error() const;
+#endif