Rtmp streams are stored as mp4 files

Hi，I want to store the rmtp stream as an mp4 file，For example, use the ffmpeg command ：ffmpeg -i rtmp://xx.com/3573613170/18573613170 -f mp4 -vcodec copy -acodec copy C:\Users\lhd\Desktop\2.mp4 But what should we do in javacv can you give me some advise? thank you! If there is some example code, that's perfect! thank you ~~

This is the code I tried to use javacv to complete this task, but the recorded video cannot be played：

        FFmpegFrameGrabber grabber = new FFmpegFrameGrabber("rtmp://xx.com/3573613170/18573613170");
        grabber.start();
        FFmpegFrameRecorder recorder = new FFmpegFrameRecorder("C:\\Users\\lhd\\Desktop\\2.mp4", grabber.getImageWidth(), grabber.getImageHeight(),grabber.getAudioChannels());
        recorder.setFormat("mp4");
        recorder.start(grabber.getFormatContext());
        LocalDateTime startTime = LocalDateTime.now();
        int times = 0;
        AVPacket avPacket = null;
        while (startTime.plusSeconds(10).compareTo(LocalDateTime.now()) > 0) {
            avPacket = grabber.grabPacket();
            if (avPacket != null) {
                recorder.recordPacket(avPacket);
                times++;
                System.out.println("record! "+times);
            }
        }
        recorder.close();
        grabber.close();

Dependent version：

        <dependency>
            <groupId>org.bytedeco</groupId>
            <artifactId>javacv-platform</artifactId>
            <version>1.5.8</version>
        </dependency>