If you like to avoid buffering when you are watching a video. You can preload that video. The YouTube app on Android devices 4.0 and up allows you to preload videos so they can offer continuous play, even when your connection is too low.
To Preload YouTube Videos With Wi-Fi to watch them fast later just follow below steps.
Open YouTube app on your Android 4.0+ device.
Now press the Menu button.
Press on the Preloading option.
Choose Subscriptions, Watch Later or you can choose both.
Press OK on the message that pops up.
Preload while connected to Wi-Fi and battery charging or you are at work and phone is lying idle.
When preloading videos, they will take up space on your Android device.