Forcing iPhone Microphone as Audio Input

Question

I am developing an iOS application (targetted specifically for iPhone, at the moment) that requires the application to record audio only from iPhone internal microphone (even when headphone/headset is plugged in), and playback at headphone (let's assumed headphone is plugged in for now).

I am wondering if this is currently possible with the available APIs? If so, can anyone please shed some light on how do I go about doing this?

Thanks!

Answer 1

I believe the answer to this question to be 'no'. I used an iPhone 4 and the new-to-iOS 4 AVFoundation to experiment, focussing on the AVCaptureDevice class.

I added the following to an application:

NSLog(@"%@", [AVCaptureDevice devices]);

So that asks that all devices that can be used for capturing audio and/or video be listed. Without the headphones plugged in, I get:

(
    "Back Camera",
    "Front Camera",
    "iPhone Microphone" 
)

With the headphones plugged in I get:

(
    "Back Camera",
    "Front Camera",
    Headphones
)

So the iPhone microphone drops off the list of available AVCaptureDevices as soon as the headphones become available. To probe this further, I added a quick bit of code to grab the AVCaptureDevice instance for the available audio device and to print its unique ID. For both the device identifying itself as "iPhone Microphone" and the device identifying itself as "Headphones", I got:

com.apple.avfoundation.avcapturedevice.built-in_audio:0

It would seem to me to be obvious that two devices can't have the same unique ID, so clearly it's the same device changing its state. Although AVCaptureDevices have a lot of stuff for setting state, it's limited to visual things like focus, exposure, flash and white balance.

Answer 2

Looks like its really not possible.

My goal is to send output to bluetooth headsets and record input from it too. As far I can see, my best options are: "PlayAndRecord + AllowBluetoothInput" property (iphone 4, nokia BH-214 headset)

IMPORTANT thing is that according to the apple documentation, you always have to RE-override your audio category when audio route changes!

THIS IS MY ROUTE CHANGE LISTENER method, that prints: RouteChangeReasons, outputRoute, audioRout:

void RouteChangeListener(void                    *inClientData,
                     AudioSessionPropertyID  inID,
                     UInt32                  inDataSize,
                     const void              *inData) {


if (inID == kAudioSessionProperty_AudioRouteChange) {

    NSLog(@"]-----------------[ Audio Route Change ]--------------------[");

    // ************************************************************************************************
    // Check route change reason **********************************************************************
    // ************************************************************************************************
    CFDictionaryRef routeDict = (CFDictionaryRef)inData;
    NSNumber* reasonValue = (NSNumber*)CFDictionaryGetValue(routeDict, CFSTR(kAudioSession_AudioRouteChangeKey_Reason));
    int reason = [reasonValue intValue];

    if (reason == kAudioSessionRouteChangeReason_OldDeviceUnavailable) {
        NSLog(@"] Logic: audio route change reason: OldDeviceUnavailable");
    }else if (reason == kAudioSessionRouteChangeReason_NewDeviceAvailable ) {
        NSLog(@"] Logic: audio route change reason: NewDeviceAvailable");
    }else if (reason == kAudioSessionRouteChangeReason_Unknown ) {
        NSLog(@"] Logic: audio route change reason: Unknown");
    }else if (reason == kAudioSessionRouteChangeReason_CategoryChange ) {
        NSLog(@"] Logic: audio route change reason: CategoryChange");
    }else if (reason == kAudioSessionRouteChangeReason_Override ) {
        NSLog(@"] Logic: audio route change reason: Override");
    }else if (reason == kAudioSessionRouteChangeReason_WakeFromSleep ) {
        NSLog(@"] Logic: audio route change reason: WakeFromSleep");
    }else if (reason == kAudioSessionRouteChangeReason_NoSuitableRouteForCategory ) {
        NSLog(@"] Logic: audio route chang reasone: NoSuitableRouteForCategory");
    }

    // ************************************************************************************************
    // Check output type ******************************************************************************
    // ************************************************************************************************
    CFDictionaryRef currentRouteDescriptionDictionary = nil;
    UInt32 dataSize = sizeof(currentRouteDescriptionDictionary);
    AudioSessionGetProperty(kAudioSessionProperty_AudioRouteDescription, &dataSize, &currentRouteDescriptionDictionary);
    if (currentRouteDescriptionDictionary) {
        CFArrayRef outputs = CFDictionaryGetValue(currentRouteDescriptionDictionary, kAudioSession_AudioRouteKey_Outputs);
        if(CFArrayGetCount(outputs) > 0) {
            CFDictionaryRef currentOutput = CFArrayGetValueAtIndex(outputs, 0);
            CFStringRef outputType = CFDictionaryGetValue(currentOutput, kAudioSession_AudioRouteKey_Type);

            if ( (CFStringCompare(outputType, kAudioSessionOutputRoute_AirPlay, 0) == kCFCompareEqualTo) ) {                // if Airplay
                NSLog(@"] Logic: output changed to Airplay");
            }
            else if ( (CFStringCompare(outputType, kAudioSessionOutputRoute_BluetoothA2DP, 0) == kCFCompareEqualTo) ) {     // if Bluetooth A2DP
                NSLog(@"] Logic: output changed to A2DP");

                // Mix with others category
                UInt32 doSetProperty = 1;
                AudioSessionSetProperty(kAudioSessionProperty_OverrideCategoryMixWithOthers,sizeof(doSetProperty),&doSetProperty);

                // Bluetooth support enable
                UInt32 allowBluetoothInput = 1;
                AudioSessionSetProperty (kAudioSessionProperty_OverrideCategoryEnableBluetoothInput,sizeof (allowBluetoothInput),&allowBluetoothInput);


            }
            else if ( (CFStringCompare(outputType, kAudioSessionOutputRoute_BluetoothHFP, 0) == kCFCompareEqualTo) ) {     // if Bluetooth HFP
                NSLog(@"] Logic: output changed to HFP");
                // Mix with others category
                UInt32 doSetProperty = 1;
                AudioSessionSetProperty(kAudioSessionProperty_OverrideCategoryMixWithOthers,sizeof(doSetProperty),&doSetProperty);

                // Bluetooth support enable
                UInt32 allowBluetoothInput = 1;
                AudioSessionSetProperty (kAudioSessionProperty_OverrideCategoryEnableBluetoothInput,sizeof (allowBluetoothInput),&allowBluetoothInput);
            }
            else if ( (CFStringCompare(outputType, kAudioSessionOutputRoute_LineOut, 0) == kCFCompareEqualTo) ) {           // if Line Out
                NSLog(@"] Logic: output changed to Line Out");
            }
            else if ( (CFStringCompare(outputType, kAudioSessionOutputRoute_Headphones, 0) == kCFCompareEqualTo) ) {        // if Headphones
                NSLog(@"] Logic: output changed to Headphone");

                // Mix with others category
                UInt32 doSetProperty = 1;
                AudioSessionSetProperty(kAudioSessionProperty_OverrideCategoryMixWithOthers,sizeof(doSetProperty),&doSetProperty);

                // Bluetooth support disable
                UInt32 allowBluetoothInput = 0;
                AudioSessionSetProperty (kAudioSessionProperty_OverrideCategoryEnableBluetoothInput,sizeof (allowBluetoothInput),&allowBluetoothInput);

            }
            else if ( (CFStringCompare(outputType, kAudioSessionOutputRoute_BuiltInSpeaker, 0) == kCFCompareEqualTo) ) {    // if Built In Speaker
                NSLog(@"] Logic: output changed to Built In Speaker");

                // Mix with others category
                UInt32 doSetProperty = 1;
                AudioSessionSetProperty(kAudioSessionProperty_OverrideCategoryMixWithOthers,sizeof(doSetProperty),&doSetProperty);

            }
            else if ( (CFStringCompare(outputType, kAudioSessionOutputRoute_USBAudio, 0) == kCFCompareEqualTo) ) {          // if USB audio
                NSLog(@"] Logic: output changed to USB Audio");
            }
            else if ( (CFStringCompare(outputType, kAudioSessionOutputRoute_HDMI, 0) == kCFCompareEqualTo) ) {              // if HDMI
                NSLog(@"] Logic: output changed to HDMI");
            }
            else if ( (CFStringCompare(outputType, kAudioSessionOutputRoute_BuiltInReceiver, 0) == kCFCompareEqualTo) ) {   // if Built in Reciever
                NSLog(@"] Logic: output changed to Built in Reciever");

                // Mix with others category
                UInt32 doSetProperty = 1;
                AudioSessionSetProperty(kAudioSessionProperty_OverrideCategoryMixWithOthers,sizeof(doSetProperty),&doSetProperty);
            }
            else {                                                                                                          // Unknown audio type
                NSLog(@"] Logic: WARNING: Unknown audio type: %@",(NSString*)outputType);
            }
        }



    }

    // ************************************************************************************************
    // Check audio route ******************************************************************************
    // ************************************************************************************************
    UInt32 routeSize = sizeof(CFStringRef);
    CFStringRef route;
    AudioSessionGetProperty(kAudioSessionProperty_AudioRoute, &routeSize, &route);
    NSLog(@"] Logic: the audio route is: %@",(NSString*)route);


    // ************************************************************************************************
    NSLog(@"]--------------------------[  ]-----------------------------[");        

}

}