Do you have 4K TV ? 4K Supported Audio Receiver ? And a 4K Device such as Fire TV 2 Box, Fire TV 3 or a CUBE or Nvida Shield.
Here is the recommended settings.
To get 4K playback on your second-generation Fire TV, the first thing you’ll do is scroll all the way to the bottom of the main screen and choose the “Settings” option.
From there, just select the first option, “Display & Sounds.”
Go down to the “Display” option, then select “Video Resolution.”
It should be set to “Auto,” which will automatically play in 4K if it’s available. If that’s not the default option, go ahead and select it now.
Amazon will tell u if your HDMI port is not compatible with 4k, if it says so, please select another HDMI port on your TV.
(This option is only available for latest fire tv firmware) if you dont see this option yet, please wait till amazon has pushed update to your device.
Next navigate to: Settings > Display & Sound > Display > Match Original Frame Rate and set it to ON.
Next Start astreamweb Play app and navigate to settings icon -> Player settings -> videos -> Adjust displayer refresh Rate -> set it to On start stop
Do not attempt to set Kodi to 4K resolution. (This is very important). Please only make the changes described above.
After making changes please restart your fire tv.