说明：  结合实例对MP4文件进行分析，重点介绍了比较重要的几个box，看后再看标准文档，更易理解。3GP文件也可以看，里面内容大致是一样的。
(MP4 files with examples of the analysis, focusing on the more important of several box, and then look to see the standard documentation, easier to understand. 3GP files can also be read, which is basically the same.)