Handler discoveryHandler = new Handler();

   public void changeToActiveDiscovery(){
        if (null != mMediaRouter && null != mMediaRouterCallback) {
            discoveryHandler.removeCallbacksAndMessages(null);
            mMediaRouter.removeCallback(mMediaRouterCallback); //TODO check if necessary
            mMediaRouter.addCallback(mMediaRouteSelector,mMediaRouterCallback, MediaRouter.CALLBACK_FLAG_PERFORM_ACTIVE_SCAN);
            discoveryHandler.postDelayed(new Runnable() {
                @Override
                public void run() {
                    changeToPassiveDiscovery();
                }
            },1000*30);
        }
    }

    public void changeToPassiveDiscovery(){
        if (null != mMediaRouter && null != mMediaRouterCallback) {
            mMediaRouter.removeCallback(mMediaRouterCallback); //TODO check if necessary
            mMediaRouter.addCallback(mMediaRouteSelector,mMediaRouterCallback,MediaRouter.CALLBACK_FLAG_REQUEST_DISCOVERY);
        }
    }