Twitch accounts for 70% of US live-streamed video

"Twitch is the No. 1 platform for streaming live video, accounting for 70% of all livestreamed hours watched during Q2 2019, per a study by StreamElements. The Amazon-owned platform experienced its first decline in viewing time with a 2% drop to 2.72 billion hours in Q2 from Q1, but still had a greater share of the market than YouTube Live (20%), Facebook Gaming (5.3%) and Microsoft's Mixer (3%).
Most of Twitch's viewing time was centered on the platform's top 5,000 streamers, which collectively generated 2 billion hours of viewing time in Q2. Popular streamers Tfue, Shroud and Ninja were in the top five every month during the quarter, while LIRIK, Asmongold and xQcOW appeared in the top five for the first time in 2019, per the study.
Streamers generated 76% of the viewing time among the top 200 channels on Twitch, compared with 24% for esports events such as the Overwatch League, ESL and Riot Games. Most viewers tend to watch popular esports games like Overwatch and League of Legends outside of a professional setting like a tournament, StreamElements' study found."
Source:  Mobile Marketer, 15th July 2019
Note - It doesn't specifically say US viewing, but I think that this is implied