Apple TV seems to be a step behind iOS in terms of "version numbers". Last night when I fired up my Apple TV (2nd Gen) and updated the software to address flickering and color issues that I've been experiencing. Through iOS 4.3, Apple added NBA League Pass (yawn) and MLB.tv (w00t) along with other minor changes show below.
TV compatibility: Addresses issues that may cause the screen to flicker or display incorrect color on some older TVs.
Wake from sleep: Addresses an issue where Apple TV may not wake up from sleep.
Audio: Addresses an issue where audio may not be heard on some TV models after switching from another input.
Stability and performance: Apple TV Software Update 4.2.1 includes stability and performance fixes for Apple TV
If you are running seas0npass on your Apple TV you will likely want to hold off on this update as with many jailbreaks.
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