go 接收 ffmpeg avpacket

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c++部分：

typedef int(*ByteFunc)(unsigned char*, int);

MYLIBDLL int byte_url(char* url, ByteFunc tcallback(unsigned char*, int size));

AVPacket packet;

tcallback((unsigned char*)&packet.data[0],packet.size);

这个也可以：

  p := (*byte)(unsafe.Pointer(r))
        // 定义一个[]byte切片，用来存储C返回的字符串
        data := make([]byte,size)
        //for *p != 0 {
        for a := 0; a < size; a++ {
            data[a] =  *p
            r+=1
            p = (*byte)(unsafe.Pointer(r))
        }

  dll := syscall.MustLoadDLL("hik_client.dll")
    callback := syscall.NewCallback(func(r uintptr, size int) (ret uintptr) {

        //var data = make([]byte, size)
        //////
        //p := (unsafe.Pointer(r))
        //q := (*[4]byte)(p)
        //copy(data[0:], (*q)[0:])
        p := (*byte)(unsafe.Pointer(r))
        // 定义一个[]byte切片，用来存储C返回的字符串
        data := make([]byte, 0)
        var index int
        index=0
        for index<size {
         data = append(data, *p)  // 将得到的byte追加到末尾
         r += unsafe.Sizeof(byte(0))  // 移动指针w，指向下一个char
         p = (*byte)(unsafe.Pointer(r))  // 获取指针的值，此时指针已经指向下一个char
         index+=1
        }
        //fmt.Printf("start send %d\n",size,len(data))
        err := conn.ws.WriteMessage(2,  data)
        if err != nil {
            fmt.Printf("conn.WriteMessage ERROR!!!\n")
        }