Windows key + R starts recording straight away ;]If you are playing on Windows 10, you can just hit the
Windows key + G. This will open the Gamebar. You can record Minecraft with it and all your videos will be saved to your "Videos" folder.
For more information: https://support.microsoft.com/en-us/help/4026387/windows-keyboard-shortcuts-for-game-bar
Keep in mind that this only works with Windows 10!