some question about FFmpegFrameGrabber

Hi, I'm using Javacv to grab mp4 file's frames to push rtmp server recently, In the file , have both video and audio streams. On the way, I met some questions:

1. how to sync the audio and video frames to rtmp? Is there some util class? or some framework code example to do this?
2. I want to push the mp4 looply, but the FFmpegFrameGrabber's restart method not works as my guess. first, cpu usage grows multi times after the function call, and stream not show on vlc correctly.

if no loop, everything is ok, but no audio and video sync only.

Here is my code, please give me some advice about my questions, Thank you!

`

    String srcfile = "./videos/video1.mp4";
    String destfile = "rtmp://127.0.0.1:1935/live/livestream";
    frameGrabber = new FFmpegFrameGrabber(srcfile);
    Frame captured_frame = null;

    try {
        frameGrabber.start();

        recorder = new FFmpegFrameRecorder(destfile, frameGrabber.getImageWidth(), frameGrabber.getImageHeight(), frameGrabber.getAudioChannels());
        //recorder.setInterleaved(true);
        recorder.setVideoOption("tune","zerolatency");
        recorder.setVideoOption("preset", "ultrafast");
        recorder.setVideoCodec(avcodec.AV_CODEC_ID_H264);
        recorder.setFormat("flv");
        recorder.setFrameRate(frameGrabber.getFrameRate());
        recorder.setVideoBitrate(frameGrabber.getVideoBitrate());
        recorder.setAudioBitrate(192000);
        recorder.setAudioOptions(frameGrabber.getAudioOptions());
        recorder.setAudioQuality(0);
        recorder.setSampleRate(16000);
        recorder.setAudioCodec(avcodec.AV_CODEC_ID_AAC);
        recorder.start();

        int total_decode_time = 0;
        int total_time = 0;
        int nLoop = 0;
        while(nLoop++ < 100){    // loop push 100 times

            while (true) {
                try {
                    captured_frame = frameGrabber.grabFrame();

                    if (captured_frame == null) {
                        System.out.println("!!! Failed cvQueryFrame");
                        frameGrabber.restart();                   // restart
                        break;
                    }

                    recorder.record(captured_frame);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }

        }
       
        // stop and release grabber and recorder, ignore...
    } catch (Exception e) {
        e.printStackTrace();
    }`