Due to some issues with Media Player and older AppleTV SW versions you’ll need to re-jailbreak with Seas0nPass before Media Player will appear as an option to install. Jailbreaking with the latest version of Seas0nPass will update your AppleTV to 4.2.2.
oh, and by the way. I did have a problem with Seas0npass. My device was originally jailbroken with Greenp0ison and installing the custom IPSW from Seas0npass failed everytime.
I used iTunes to install the original Apple 4.2.2 IPSW which worked fine, after that there where no problems re-jailbreaking with Seas0npass.