FFmpegFrameGrabber grabImage() takes too long time.

Hi ! I meet a problem about this function , FFmpegFrameGrabber grabImage(),when I use sdp as grabber's source. If the sdp connection doesn't have any frame , the grabber.grabImage() will spend time about 10s then return null. Is there any solution to let this function return null immediately? I tried something methods like setOption("stime","1") , setTimeout(1),setOption(TimeoutOption.TIMEOUT.getKey(),String.valueOf(TIMEOUT * 50000))...These didn't work.Below is my code. Thanks for your reply!

FFmpegFrameGrabber grabber;	
FFmpegFrameRecorder recorder = null;

grabber = new FFmpegFrameGrabber("1111.sdp");
grabber.setVideoOption("vcodec", "copy");
grabber.setAudioChannels(0);
grabber.setOption("protocol_whitelist", "file,udp,rtp");
grabber.setTimeout(1);
grabber.setMaxDelay(1);
grabber.setOption("stime", "1");
grabber.delayedGrab(1);
grabber.setOption
(
        TimeoutOption.TIMEOUT.getKey(),
        String.valueOf(TIMEOUT * 50000)
);
grabber.start();


String fileName = "sample_rtp_out.h264";
recorder = new FFmpegFrameRecorder(fileName, 640, 480, 0);
recorder.setVideoCodec(avcodec.AV_CODEC_ID_H264); 
recorder.setFormat("h264");
recorder.setVideoOption("re", "");
recorder.setVideoOption("vcodec", "copy");
recorder.setAudioChannels(0);
recorder.start();

Frame frame;
while (true)
{
	
	frame=grabber.grabImage();
	
    if(frame!=null)
    {
        recorder.record(frame);
    }else
    {
    	    break;
    }
}

recorder.stop();
recorder.release();
grabber.stop();