The video storyline is as follows (it's simplistic and only largely true, and that's intentional):

Part 1: The power of video as a medium

• People spent a large chunk of the late 20th century watching television. By the 90s TV was more powerful than practically any other medium in existence. Powerful due to a) Time spent b) 'Hypnotic' effect i.e. undivided attentio.
• People continue to spend a quarter (on average) of their waking day watching TV - but increasingly on personal devices (laptops, tablets, smartphones)

Part 2: The power of social/mobile, and video 2.0, as seen through social network evolution:

• First - Text-driven online social networks (like Yahoo! Messenger, Orkut, Myspace etc.)
• Next - Text & multimedia driven online social networks and the advent of online social video (Facebook, Twitter, YouTube)
• Next - Mobile Multimedia social networks (Whatsapp, Instagram). Around this time, social video content started exploding, courtesy  Buzzfeed etc.
• Next - Mobile video social networks (Snapchat kicked it off, and soon Instagram 2.0). Now even Linkedin has joined in.

Part 3: Mobile video advertising spends are growing, and the ad revenue model is increasingly viable for startups in mobile.

• No story needed - just see this recent post about Pinterest and this about Snapchat's 360 degree videos for a quick sense.

Putting 2/2 together, it's basically a mix of mobile, social, and video. 

Even huge corporations like Warner Bros are waking up to this reality and their investment in Hulu that values the company at $5.8bn shows their belief in mobile/digital video. Knowing that large corporations are (usually) slightly behind the curve on innovative investments - they're going for the relatively proven bets (online + mobile video).

But the next unicorn in media will be a mobile-social-video platform. Parts 2/3/4 of this series will cover some specific businesses that fill current-day gaps.