android停止默认视频录制以获得音频焦点

我正在做一个示例Voip应用程序。当用户使用默认的camera应用程序录制视频时，出现了输入Voip呼叫的情况，我想停止视频录制，以便将音频焦点转到我的应用程序

mAudioManager.requestAudioFocus(mAudioFocusListener, AudioManager.STREAM_MUSIC, AudioManager.AUDIOFOCUS_GAIN);

private OnAudioFocusChangeListener mAudioFocusListener = new OnAudioFocusChangeListener() {

    @Override
    public void onAudioFocusChange(int focusChange) {

        Logger.d(TAG, "--------Audio Focus change: " + focusChange);

        switch(focusChange){
            case AudioManager.AUDIOFOCUS_GAIN:
                Logger.d(TAG, "--------Focus change: AUDIOFOCUS_GAIN" );
                break;
            case AudioManager.AUDIOFOCUS_GAIN_TRANSIENT:
                Logger.d(TAG, "--------Focus change: AUDIOFOCUS_GAIN_TRANSIENT" );
                break;
            case AudioManager.AUDIOFOCUS_GAIN_TRANSIENT_MAY_DUCK:
                Logger.d(TAG, "--------Focus change: AUDIOFOCUS_GAIN_TRANSIENT_MAY_DUCK" );
                break;
            case AudioManager.AUDIOFOCUS_LOSS:
                Logger.d(TAG, "--------Focus change: AUDIOFOCUS_LOSS" );
                break;
            case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT:
                Logger.d(TAG, "--------Focus change: AUDIOFOCUS_LOSS_TRANSIENT" );
                break;
            case AudioManager.AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK:
                Logger.d(TAG, "--------Focus change: AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK" );                 
                break;
            case AudioManager.AUDIOFOCUS_REQUEST_FAILED:
                Logger.d(TAG, "--------Focus change: AUDIOFOCUS_REQUEST_FAILED" );
                break;


        }
    }
};    

当手机本机摄像头录制视频时，如何获得音频焦点