Utilize the input text as a context reference, choose the right relationship between medium and San Francisco from the options. Options: product/material produced, manufacturer, distributed by, industry, position held, original broadcaster, owned by, founded by, distribution format, headquarters location, stock exchange, currency, parent organization, chief executive officer, director/manager, owner of, operator, member of, employer, chairperson, platform, subsidiary, legal form, publisher, developer, brand, business division, location of formation, creator.

SAN FRANCISCO, Sept 25 Video gamers who live-stream their matches online and the throngs of fans who tune in daily to watch them swarmed a first-of-its kind convention in San Francisco on Friday, as interest swells in the medium of online video game broadcasting.

Answer: headquarters_location