this is what i have googled for your reference:
"However, using the $5 OPlayer HD iPad app, I was able to play media files in any format on my iPad. OPlayer can recognise and play a wide variety of files and links to the GoFlex through http streaming – typing in any web address in its own built-in browser opens up the GoFlex interface."
Please also check the videos:
http://www.youtube.com/watch?v=zQ3NgSHCMOg