AVPlayer的一些基本用法，缓存监听等
#define URLSTR_LIUCHANG @"https://portalvhdslhjkp62sbd1zh.blob.core.chinacloudapi.cn/upload/9533522808.f4v.mp4"设置属性：@property(nonatomic, strong)AVPlayer *player;@property(nonatomic, strong)AVPlayerIt
