setAudioChannelCallback method
Implementation
void setAudioChannelCallback(String channel, Function f) {
Map<String, String> map =
generateMessage(MessageType.SET_AUDIO_CHANNEL_CALLBACK, content: "");
map[MessageTag.CHANNEL_NAME] = channel;
_callbackList.add(f);
map[MessageTag.CALLBACK_INDEX] = _callbackList.length.toString();
_sendPort.send([map, _callbackPort.sendPort]);
}