The Apple TV 4, released in late 2015, can be used as a frontend for MythTV with a third party app.
Frontend on Apple TV 4
There have been several generations of the Apple TV. The Apple TV 4, late 2015, marks a significant change in the lineup as there is now an app store. Almost immediately after this version launched, a developer made available an app to playback MythTV recordings. (Search the app store for "MythTV". The app is so new at this point that the developer doesn't have a web site yet.) Initial user reports have been quite favourable with success playing US broadcast HD recordings (MPEG2 format) via wifi connection.
A screen shot of the main recordings screen is shown below:
The Apple TV 3 remains for sale, as of December 2015. Note that this version can NOT install third party apps. It can not easily be used as a frontend for MythTV.
The original Apple TV could be jail broken and have Linux installed. This version has not been sold in several years, however. Guides are available elsewhere on this wiki for installing Linux and running MythTV on the device.