Why do people put ads in front of YouTube videos sometimes?

Well, technically it's YouTube that serve the "pre-roll" ads before the videos you watch, and they then share earnings with the people who created the video (if they opt in to that program).

YouTube is owned by Google, so the ads are actually part of Google's ever-expanding ad network - and advertisers can pay for a certain amount of impressions, or a fixed post per click on their ad.

It's not great having ads everywhere on the internet, I have to admit, but on the other hand - there are a bunch of free services we all enjoy which simply wouldn't be here without advertising revenue.

What's REALLY crazy is that YouTube earned around $4 billion last year, but it's suggested they didn't even turn a profit (http://www.wsj.com/articles/viewers-dont-add-up-to-profit-for-youtube-1424897967).

Apparently, paying content creators and managing the infrastructure required to deliver videos to the world costs around as much as they're making!