ftp AVOptions:
-timeout <int> ED........ set timeout of socket I/O operations (from -1 to INT_MAX) (default -1) 超时
-ftp-write-seekable <boolean> E......... control seekability of connection during encoding (default false)
-ftp-anonymous-password <string> ED........ password for anonymous login. E-mail address should be used.匿名登陆的密码，一般是邮件。
-ftp-user <string> ED........ user for FTP login. Overridden by whatever is in the URL.登陆用户名
-ftp-password <string> ED........ password for FTP login. Overridden by whatever is in the URL.登陆密码