Filled side_ data not received correctly（javacv 1.5.9）

my app:project A send side_data To B I used mediamtx as the RTSP server
java code: A:

        private static String inputUrl = "rtsp://localhost:8554/stream";
        private static String outputUrl = "rtsp://localhost:8554/stream1";
        FFmpegFrameGrabber grabber = new FFmpegFrameGrabber(inputUrl);
        grabber.setOption("rtsp_transport", "tcp");

        grabber.start();
        FFmpegFrameRecorder recorder = new FFmpegFrameRecorder(outputUrl, grabber.getImageWidth(), grabber.getImageHeight());
        recorder.setVideoCodec(AV_CODEC_ID_H264);
        recorder.setOption("rtsp_transport", "tcp");
        recorder.setPixelFormat(AV_PIX_FMT_YUV420P);
        recorder.setFormat("rtsp");
        recorder.start(grabber.getFormatContext());
        AVPacket packet = null;
        while ((packet = grabber.grabPacket()) != null) {

            BytePointer retrievedData = av_packet_new_side_data(packet, AV_PKT_DATA_NEW_EXTRADATA, extradata.length);
            retrievedData.put(seiBytes,0,seiBytes.length);
            // Consistent with the 'extradata' filled in
            System.out.println(Arrays.toString(av_packet_get_side_data(packet, AV_PKT_DATA_NEW_EXTRADATA, new SizeTPointer()).getStringBytes()));
            recorder.recordPacket(packet);
            avcodec.av_packet_unref(packet);
        }

B:

        private static String inputUrl = "rtsp://localhost:8554/stream1";
        FFmpegFrameGrabber grabber = new FFmpegFrameGrabber(inputUrl);
        grabber.setOption("rtsp_transport", "tcp");
        // retrievedData is null
        BytePointer retrievedData = av_packet_get_side_data(avPacket, AV_PKT_DATA_NEW_EXTRADATA, new SizeTPointer());
        

How should I modify the code so that the A can transmit the side correctly_ Data to B