/** Retrieves the volume of the current audio playback device.
         *
         * @return
         * - The volume of the current audio playback device, if this method call succeeds.
         * - < 0: Failure.
         */
        public override int GetAudioPlaybackDeviceVolume()
        {
            if (mEngine == null)
            {
                return((int)ERROR_CODE.ERROR_NOT_INIT_ENGINE);
            }

            return(IRtcEngineNative.getAudioPlaybackDeviceVolume());
        }