Twitch, the Amazon-owned video streaming service where viewers watch other people play video games, has outgrown its niche roots to the point that 1 million people on average are using it at any given time.

The broader category of esports has blossomed into an international phenomenon, with research firm Newzoo predicting the market will grow 55 percent by 2020 to $1.4 billion. That kind of success brings with it competition from big media and tech companies looking for new areas of growth.

"One of the biggest changes for Twitch over the past year is just the way that video games and streaming have started to cross over into the mainstream," CEO and co-founder Emmett Shear told CNBC in an interview last weekend in San Jose, California, at the company's annual TwitchCon event.

Facebook recently added to its Gaming Creator pilot program, aiming to give content producers more tools. And in September, 21st Century Fox invested $100 million into social broadcasting platform Caffeine, which is dedicated to producing exclusive esports, video gaming, live entertainment and sports content.

"I think the difference between Twitch and any competition is that degree of hyperfocus on the streamer," Shear said. "As a result, we just build better tools and a great community for that."

Four years after Amazon shelled out $970 million for Twitch, Shear remains in expansion mode. Much of that was on display at TwitchCon, where tens of thousands of fanatics descended on Silicon Valley and millions of dollars in prize money was paid out to winners. The final weekend of Fortnite's $10 million Fall Skirmish tournament took place at the event and drew in over 4 million unique viewers, who tuned in to watch almost 24 hours of cumulative live-streamed content.