Is it possible to pre-download a YouTube video to view it later offline? I have the Galaxy S3, and I'd like to watch YouTube videos during my commutes. I like to watch long videos (around 1 hours), so I have no more than 1 video per commute. 

However, youtube video takes a lot of bandwidth and I have a cap on data usage. Besides, connection outside during peak hours tend to be slow, which makes the video pause to download a lot of times. 

Is it possible to pre-download a video at home (using my Wi-Fi, which is faster and has no data cap), and watch it on the way? I tried pausing it at home and let it download, but whenever the phone sleep (it sleeps often!), or the application switch from youtube to anything else, it seems all previous download will be lost.
Update:

YouTube has removed this feature. Source



YouTube's official app allows you to preload a video. You can either preload all your subscription or the videos you have added to watch later.

When your phone is connected to WiFi and charger, Youtube automatically pre-loads them.

Open Youtube -> Settings -> Preloading

One thing to note is that this still requires data connection to view the pre-loaded video. It won't download the videos but it does something (may be verification) before showing pre-loaded videos.

Read more at support doc