For those of you who have jailbroken your AppleTV (2nd Gen Black), you probably have installed the killer media player XBMC. But on iOS 4.3, Apple changed some hardware calls and this broke support for hardware decoding, meaning XBMC would crash when trying to play any x264 encoded content. Fortunately, the excellent developers have now rectified the problem and have incorporated the changes into the latest iOS nightly builds.
These builds can’t be installed through NitoTV or by using apt-get update as you normally would, because they haven’t been added to the official repo. You’ll need to SSH in and run a few commands.
This thread over at the XBMC forums provides all the details.