According to ew.com the Mariah perf. was pre-taped, but apparently she sang live...details below.
"Please, no judging," Mariah smiled, as she began warbling some notes into her bedazzled mic. "I don't even know if they can hear in the audience," she continued, then turned to us and explained. "They make us wear these headphone things, and it's so bleak! Just FYI. Sorry to, like, have a sound check. I'm always late." My goodness, Mariah, don't apologize! We are happy to sit here and listen to you sing the same song four or five times.
We pre-tape Mariah, whose segment will air after the Q&A segment we'll pre-tape right after we pre-tape Mariah. Mariah finishes the song, does her little confab with Ryan, and once the cameras are off, Ryan asks, "Randy, how did it sound?" "Great!" replies Randy. "The ending was a little rancid," Mariah says casually. "NO!" screams the audience. I write +10 for use of "rancid" in my notebook.
ew.com
Laughter is much more important than applause. Applause is almost a duty. Laughter is a reward.
Carol Channing