You may not know it, but Android TV can take screenshots like a phone or tablet. Unfortunately, this's not so simple, but we'll show you a method that works.
Some Android TVs, such as the Nvidia Shield TV, include a built-in screenshot tool. However, most devices do not have this, so you need to be a little more creative to take a screenshot on these devices.
This method requires a paid third-party application called "Button Mapper", which allows you to map ενέργειες any button on your remote control.
When you first start it, the application will ask you to start the service accessibility. This allows the application to locate the buttons you press - click "OK".
In the Settings menu that opens, scroll down, then select "Device Preferences".
Scroll down and select "Accessibility".
Find and select "Button Mapper" in the list.
Activate the "Enable" button for Button Mapper and then click "OK" on the confirmation page.
Returning to the Mapper Button application, you will see an icon locking next to some of them buttons. These require the purchase of $ 4,99 (in-app) for configuration. Select the button you want to use to take a screenshot. We chose the "Menu Button".
Then turn it on choice "Customize" at the top.
Then you can decide what button action you want to use to take a screenshot. We chose "Double Tap".
Make sure "Actions" is selected at the top of the pop-up window, then scroll down and select "Screenshot".
Now, every time you use his energy button you specified, you will receive a screenshot.
You can find the screenshots in the Photos & Videos application that is pre-installed on your Android TV or device.
Source of information: howtogeek.com