When to get data from recorder's stream

I tried this for record sample data

PipedOutputStream pos=new PipedOutputStream();
FFMpegFrameRecorder recorder=new FFmpegFrameRecorder(pos,channels);
PipedInputStream pis=new PipedInputStream(pos,640000)；
...setRecorder...
recorder.start();
....get frame from somewhere...
while((frame!=null){
     recorder.record(frame);
     while(pis.avaliable()>0){
          pis.read(new byte[2048]);
    }
    frame.close();
}

I run this code for a while and the JVM crushed. Location is swr_convert called by recordSample() As I known. the data in frame won't be put in the stream immediately when the recorder.record(sample) is called. Usually I can only get the date from pis after several frame is recorded(for example 10frames) So I think this problem may be caused by I closing the frame before the data is dump into the stream actually. But I have to close this frame. some flush methods from recorder、pos、pis. I alse tried these. but no effect. Do you have some idea on how to flush the frame data into pis immediately? Looking forward to your reply