Remove AVAudioSessionPortBuiltInMic as an option

Question

I would like to remove the iPhone's built in mic as an option. Only the one that comes out the headset though. Basically I want to force output to either headphones/bluetooth (if available) or the main speaker. Apple hasn't documented a way to remove a port. Would it be possible to intercept route changes and if they select a mic force it to a speaker?

Answer 1

Yes, it's possible to intercept route changes. You need to observe for AVAudioSessionRouteChangeNotification notification:

    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(audioRouteDidChanged:)
                                                 name:AVAudioSessionRouteChangeNotification
                                               object:nil];

then you will be able to distinguish route change type:

- (void)audioRouteDidChanged:(NSNotification *)notification
{
    // Here you can figure out the why audio route has been changed (if you need it)
    AVAudioSessionRouteChangeReason reason = [notification.userInfo valueForKey:AVAudioSessionRouteChangeReasonKey];
    switch (reason)
    {
        case AVAudioSessionRouteChangeReasonNewDeviceAvailable:
            NSLog(@"A user action (such as plugging in a headset) has made a preferred audio route available.");
            break;

        case AVAudioSessionRouteChangeReasonOldDeviceUnavailable:
            NSLog(@"The previous audio output path is no longer available.");
            break;

        default:
            NSLog(@"Other reasons. See documentation");
            break;
    }

    // And then make a decision to disable earpiece(aka receiver).
    // You can request current audio route description
    AVAudioSessionRouteDescription *routeDescription = [AVAudioSession sharedInstance].currentRoute;
    // then traverse through outputs and figure out if headset is present
    __block BOOL headsetExists = NO;
    [routeDescription.outputs enumerateObjectsUsingBlock:^(AVAudioSessionPortDescription *obj, NSUInteger idx, BOOL *stop) {
        if ([obj.portType isEqualToString:AVAudioSessionPortHeadphones])
        {
            headsetExists = YES;
            return ;
        }
    }];

    if (headsetExists == NO)
    {
        // force sound to speaker
        NSError *err = nil;
        [[AVAudioSession sharedInstance] overrideOutputAudioPort:AVAudioSessionPortOverrideSpeaker
                                                           error:&err];
    }
}