With Ed Sheeran on the witness stand in Manhattan federal court on Tuesday during a copyright trial, jurors were warned to keep their composure while watching a video of the British pop star performing a medley of his hit song "Thinking Out Loud" and the classic Marvin Gaye tune "Let's Get it On."

"We don't allow dancing," U.S. District Judge Louis Stanton instructed the seven-member jury.

Lawyers for heirs of songwriter Ed Townsend, Gaye's co-writer on the 1973 hit, showed the video to bolster their allegation that Sheeran, his label Warner Music Group and music publisher Sony Music Publishing owe them a share of the profits for allegedly copying the song.

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Ben Crump, a lawyer for the heirs, said in his opening statement that the performance amounted to a "confession" by Sheeran.

Under questioning from Keisha Rice, another lawyer for the plaintiffs, Sheeran said many pop songs use the same three or four chords, and that he performs "mash-ups" of many songs at his concerts.

"You could go from 'Let it Be' to 'No Woman, No Cry' and switch back," Sheeran testified, referring to the Beatles and Bob Marley classics. "If I had done what you're accusing me of doing, I'd be a quite an idiot to stand on a stage in front of 20,000 people and do that."

The trial is the first of three Sheeran could face from lawsuits over similarities between the two hits. In her opening statement, Sheeran's lawyer Ilene Farkas, said the two songs are distinct and told jurors that the plaintiffs should not be allowed to 'monopolize' a chord progression used in countless songs.

Sheeran at one point grew frustrated when Rice cut off his response about the medley. "I feel like you don't want me to answer because you know that what I'm going to say is actually going to make quite a lot of sense," he said.

Sheeran is expected to testify again later in the trial as part of the defense case. If the jury finds Sheeran liable for copyright infringement, the trial will enter a second phase to determine how much he and his labels owe in damages. The first trial is expected to last about a week.