Dealing with Audio Output Hardware 處理音頻輸出硬件設備

Users have a number of alternatives when it comes to enjoying the audio from their Android devices. Most devices have a built-in speaker, headphone jacks for wired headsets, and many also feature Bluetooth connectivity and support for A2DP audio.

Check What Hardware is Being Used
How your app behaves might be affected by which hardware its output is being routed to.

You can query the AudioManager to determine if the audio is currently being routed to the device speaker, wired headset, or attached Bluetooth device as shown in the following snippet:

if (isBluetoothA2dpOn()) {
    // Adjust output for Bluetooth.
} else if (isSpeakerphoneOn()) {
    // Adjust output for Speakerphone.
} else if (isWiredHeadsetOn()) {
    // Adjust output for headsets
} else {
    // If audio plays and noone can hear it, is it still playing?
}//http://blog.csdn.net/sergeycao
Handle Changes in the Audio Output Hardware
When a headset is unplugged, or a Bluetooth device disconnected, the audio stream automatically reroutes to the built in speaker. If you listen to your music at as high a volume as I do, that can be a noisy surprise.

Luckily the system broadcasts an ACTION_AUDIO_BECOMING_NOISY intent when this happens. It’s good practice to register a BroadcastReceiver that listens for this intent whenever you’re playing audio. In the case of music players, users typically expect the playback to be paused—while for games you may choose to significantly lower the volume.

private class NoisyAudioStreamReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        if (AudioManager.ACTION_AUDIO_BECOMING_NOISY.equals(intent.getAction())) {
            // Pause the playback
        }
    }
}

private IntentFilter intentFilter = new IntentFilter(AudioManager.ACTION_AUDIO_BECOMING_NOISY);

private void startPlayback() {
    registerReceiver(myNoisyAudioStreamReceiver(), intentFilter);
}

private void stopPlayback() {
    unregisterReceiver(myNoisyAudioStreamReceiver);