OpenAI is shutting down its social media app Sora, which went viral last autumn as a place to share short-form videos generated by artificial intelligence (AI) but also raised alarms in Hollywood and elsewhere. OpenAI said in a brief social media message Tuesday that it was “saying goodbye to the Sora app” and would share more soon about how to preserve what users had already created. “What you made with Sora mattered, and we know this news is disappointing,” it said.