Twitter on Tuesday launched enhanced video services that will allow users to post longer videos — up to 140 seconds. It also announced a new platform for celebrities and public figures to share their stories. Because sports, news, music and other videos increasingly are the type of content that goes viral on Twitter, the company decided to expand content parameters, noted Jeremy Rishel, head of product development for creators. “Video is becoming increasingly central to the real-time conversations happening on Twitter video.”