Detect when sound is playing through earpiece speaker

Background

I'm developing an app that monitors the proximity sensor. However, I don't want to monitor the sensor while the user is listening to something through the phone ear speaker. This is because the user will probably have his/her head against the handset to listen, which in turn triggers the proximity sensor, and I'm not trying to detect head proximity.

Question

How can I detect when sound is and isn't playing through the handset ear speaker? Callbacks are preferable, of course, but I'm willing to poll if it's the only way.

You can approximate this by regularly polling and making the following checks:

• Check if the audio system is not in normal mode.
• Check if the audio is being routed to the earpiece.

I tested this in Android 4.3, and it seemed to work fine with the system phone app, Viber and Skype. However, it doesn't seem to detect music or non-telephony sounds played through the earpiece. I don't think this is much of a problem, because the earpiece generally seems to only be used for telephony anyway.

Example

public class EarpieceSpeakerState {

    private AudioManager audioManager;

    public EarpieceSpeakerState(AudioManager audioManager) {
        this.audioManager = audioManager;
    }
    
    public boolean usingEarpieceSpeaker() {
        return playingSound()
            && routingToEarpiece();
    }

    private boolean playingSound() {
        return audioManager.getMode() != AudioManager.MODE_NORMAL;
    }
    
    private boolean routingToEarpiece() {
        return !(
            audioManager.isSpeakerphoneOn()
            || audioManager.isBluetoothScoOn()
            || audioManager.isBluetoothA2dpOn()
            || audioManager.isWiredHeadsetOn()
        );
    }

}