iOS: AVSpeechSynthesizer : need to speak text in Headphone left channel - ios

Question

I am using AVSpeechSynthesizer for TextToSpeech. I have to play the speak in HeadPhone left Channel (Mono 2). I have got the following to set the output channel.
func initalizeSpeechForRightChannel(){
let avSession = AVAudioSession.sharedInstance()
let route = avSession.currentRoute
let outputPorts = route.outputs
var channels:[AVAudioSessionChannelDescription] = []
//NSMutableArray *channels = [NSMutableArray array];
var leftAudioChannel:AVAudioSessionChannelDescription? = nil
var leftAudioPortDesc:AVAudioSessionPortDescription? = nil
for outputPort in outputPorts {
for channel in outputPort.channels! {
leftAudioPortDesc = outputPort
//print("Name: \(channel.channelName)")
if channel.channelName == "Headphones Left" {
channels.append(channel)
leftAudioChannel = channel
}else {
// leftAudioPortDesc?.channels?.removeObject(channel)
}
}
}
if channels.count > 0 {
if #available(iOS 10.0, *) {
print("Setting Left Channel")
speechSynthesizer.outputChannels = channels
print("Checking output channel : \(speechSynthesizer.outputChannels?.count)")
} else {
// Fallback on earlier versions
}
}
}
I have 2 problems in the code
1. Cant able to set outputchannels , It always nil (It is happening on first time calling this method, consecutive calls working fine)
2. outputchannels supports from iOS 10.* But I need to support it from iOS
8.0
Please provide the best way to do that.

Answer 1

Instead of checking the channelName, which is descriptive (i.e. for the user), check the channelLabel. There is an enumeration containing the left channel.
I suspect this may not be possible pre-iOS 10. AVAudioSession doesn't appear to have any method to select only the left output channel. You may be able to use overrideAudioPort:error but it would affect the entire app.