1、URL Tag Validation
2、Special format of URL for preventing unauthorized usage and access
Original: http://www.baidu.com/2016/0704/8025915_HD-60i_7198.mp4
Using UTV:http://www.baidu.com/2016/0704/8025915_HD-60i_7198.mp4?px-time=1467685158&px-hash=a08a3c149514aae2aea14755a45a29c2
px-time : current time or expire time
px-hash : hash(secret + url_path +expire_time)
原文：http://www.cnblogs.com/nopnog/p/7452405.html