创建一个大文件 从令一个avi文件中读取数据 对新创建的大文件进行写操作 然后对写入的数据进行MD5值校验 确保对大文件的写入正确-Create a large file from a avi file so that read data on the newly created big file and then write the data to write MD5 checksum value to ensure that the correct write large files