Betamax was a video recording format released by Sony that lost out to VHS in the 1970s and 1980s, though it was favoured by commercial video camera operators. However, when Betamax was initially released and common use for consumers was to record and watch TV shows at their leaser, importantly often fast-forwarding through commercials (undermining the economic rational of US TV stations.)
In the Betamax case, i.e., Universal City Studios v. Sony Corp., 464 U.S. 417 (1984) the US Supreme Court Universal asserted that by selling Betamax video recorders that could be programmed to record off-air broadcast programming at specific times, Sony was a Secondary Infringer by providing the means by which owners of the machines recorded copies of broadcast programs, especially movies whose copyright was owned by Universal.
The Supreme Court decision turned on the question of whether recording copyrighted broadcast programming by owners of Betamax video recorders (which had timing functions to facilitate such recording and fast-forward functions to circumvent watching commercials) was infringing. The Supreme Court held that it was not, and absent underlying acts of infringement, there could be no Secondary Infringement by Sony.
There’s very little escaping the fact that the Supreme Court’s reasoning was at best dubious and the decision has been cut back significantly since. It’s plausible to suggest that, since by the time the case reached the Supreme Court, approximately a sixth of US households owned video recorders, either Betamax or VHS, including probably some of the justices themselves, the Court balked at a finding that tens millions of US households were committing copyright infringement.
The effect of the Betamax case was modified somewhat by Digital Millennium Copyright Act of 1998 modified some aspects of copyright law and in MGM Studios, Inc. v. Grokster, Ltd., 545 U.S. 913 (2005) the Court distinguished its decision in a manner that isn’t very consistent with the logic of the Betamax case. Ironically, Sony was by that time a major owner of content and supported the decision’s prohibition of file sharing as inducing copyright infringement.