To connect your Xbox One to your TV so that you can control the volume and power of you TV via your Xbox One, you must do the following steps:

1.Go Onto Settings (Found under My games & apps)
2.Click 'TV & OneGuide Settings'
3.Click 'Devices'
4.Select Your TV Brand (available brands are: LG, Panasonic, 5.Samsung, Sharp, Sony, Toshiba, VIZIO) Then click 'Next'
6.Click 'Automatic'
7.Click 'Send Command' and this shouuld mute your TV, If it does click 'Yes', If not click 'No'
8.If Clicked 'Yes' Skip to Point 9
9.If Clicked 'No' then it will try various signals to figure out your TV model, if this is still now working it will ask for you to enter your TV model manually.
10.Now click 'B' to go back to 'TV & OneGuide Settings' Then click 'Power Settings'
11.Select '"Xbox One" Turns on my devices' and '"Xbox turn off" Turns off my TV'

You can now command your Xbox One to turn volume up or down, use smartglass to adjust volume and turn the Xbox One and TV on or off together.