Ever since Netflix started mailing out movies on DVDs in the late 1990s, the entertainment company has been dreaming up ways to keep people sitting on their couches, watching stuff. Its red envelopes helped sound the death knell for the neighborhood video store, and the launch of its video streaming service in 2007 heralded the frictionless age of TV-by-internet. Now Netflix has more than 300 million subscribers — and is aiming to acquire Warner Bros. Discovery Inc. for $83 billion in the hopes that its enormous catalog will bring in even more.