请通过：
http://bytepadding.com/big-data/map-reduce/understanding-map-reduce-the-missing-guide/

Lets try to understand what is the problem . 
1. One takes a file and divides it into fileSplits. 
2. Each split is consumed by one mapper. 
3. How do you make sure a record in the file is not split across two file splits. 
4. A record cant be ignored nor read partially. 
5. A InputFormat takes care of carefully splitting the file and handling situations when a record is split at the boundary of file splits. 
6. Hadoop has varios inpuit formats like TextInputFormat, KeyValueTextInputFormat

试着找到一个输入格式，可以用于您的视频文件或自己写一个。fileinputformat是所有文件的基类。