Error of FFmpeg on Java in "av_image_copy_to_buffer" method during decoding H.264 stream

I'm trying to decode H.264 stream, which is sent over Socket from an Android application to a computer. And I also want to show the decoded stream using JavaFX. I searched for a long time, and decided to use JavaCV / FFmpeg. However I got error from FFmpeg. (I was inspired by this code.)

Questions:

• Why does FFmpeg make error?
• Is it a correct way to convert AVFrame to javafx.scene.image.Image?

I'm using:

• javacv-platform 1.4.4
• ffmpeg-platform 4.1-1.4.4

Code:

This is a part of import and class fields, and method which runs once at the first time. (Actually the content of initialize() is wrapped by try~catch.)

    import javafx.scene.image.Image;

    private avcodec.AVCodec avCodec;
    private avcodec.AVCodecContext avCodecContext;
    private avutil.AVDictionary avDictionary;
    private avutil.AVFrame avFrame;

    public void initialize() {
        avCodec = avcodec_find_decoder(AV_CODEC_ID_H264);
        if (avCodec == null) {
            throw new RuntimeException("Can't find decoder");
        }
        avCodecContext = avcodec_alloc_context3(avCodec);
        if (avCodecContext == null) {
            throw new RuntimeException("Can't allocate decoder context");
        }
        int result = avcodec_open2(avCodecContext, avCodec, (AVDictionary) null);
        if (result < 0) {
            throw new RuntimeException("Can't open decoder");
        }
        avFrame = av_frame_alloc();
        if (avFrame == null) {
            throw new RuntimeException("Can't allocate frame");
        }
    }

And this is a method which is called every time when I receive a packet from Android. byte[] data is the packet data starting with 0x00, 0x00, 0x00, 0x01.

The place where I get error is number_of_written_bytes. It always gets <0.

    private void decode(byte[] data) {
        AVPacket avPacket = new AVPacket();
        av_init_packet(avPacket);
        avPacket.pts(AV_NOPTS_VALUE);
        avPacket.dts(AV_NOPTS_VALUE);
        BytePointer bytePointer = new BytePointer(data);
        bytePointer.capacity(data.length);
        avPacket.data(bytePointer);
        avPacket.size(data.length);
        avPacket.pos(-1);

        avcodec_send_packet(avCodecContext, avPacket);
        int result = avcodec_receive_frame(avCodecContext, avFrame);
        if (result >= 0) {
            int bufferOutputSize = av_image_get_buffer_size(avFrame.format(), avFrame.width(), avFrame.height(), 16);
            Pointer pointer = av_malloc(bufferOutputSize);
            BytePointer outputPointer = new BytePointer(pointer);
            int number_of_written_bytes = av_image_copy_to_buffer(outputPointer, bufferOutputSize, avFrame.data(), avFrame.linesize(), avFrame.chroma_location(), avFrame.width(), avFrame.height(), 1);
            if (number_of_written_bytes < 0) {
                //The process always come here.
                throw new RuntimeException("Can't copy image to buffer");
            }

            System.out.println("decode success");
            Image image = new Image(new ByteArrayInputStream(outputPointer.asBuffer().array()));
        } else {
            System.out.println("decode failed");
        }
    }

Anything is helpful for me. Thanks.