This depends on the set-top box you're using. Not all settop-boxes will support device rotation. If you think about it - there is no sense to it, as a user will not typically rotate a settop-box connected to a tv :) This is to the discretion of the Settop-box developer if they want to support it or not. I would try to find and install a number of 3rd party apps which rotates the display and work on regular smartphones, and test them on the same set top box. This will give you a good idea, or if you can - contact the developer of the set top box and ask them.