Mr Kelly faces up to 15 years in jail if convicted
Jurors in US R&B star R Kelly's child pornography trial have watched the sex video at the centre of the case.
On the opening day of the trial in Chicago, prosecutors played the video of a man having sex with a young woman.
Prosecution lawyers allege the "vile" video is of Mr Kelly and a girl who was as young as 13 when it was filmed.
Mr Kelly denies filming himself having sex with an underage girl and his lawyer said the video showed neither him nor the alleged victim.
The star, whose hits include She's Got That Vibe and I Believe I Can Fly, faces up to 15 years in jail if convicted.
The girl who is alleged to be in the 27-minute tape is now 23 and says it was not her in the footage.
In Tuesday's opening arguments, prosecutor Shauna Boliker told the jury they would "see the sex acts he commands her to do".
"Acts you have never seen before.
"Vile, disturbing and disgusting sex acts, actions that were choreographed, produced and starred in by Robert Kelly."
Ms Boliker said she would not be calling the alleged victim to the stand but did not explain why.
Defence lawyer Sam Adam Jr said the video, made between 1998 and 2000, was "at best, a copy of a copy of a copy".
He said Mr Kelly had a significant mole on his lower back and that the man on the tape did not have the mole.
Mr Adam said neither the FBI nor "a single witness" could identify the man in the tape as Mr Kelly.
Mr Kelly sat grim-faced through the hearing, the Associated Press news agency reported.
The tape was originally posted to the Chicago Sun-Times newspaper in 2002. The paper then handed it to police.
Mr Kelly was charged four months later with 21 counts relating to child pornography and released on $750,000 (£383,000) bail. Seven of the charges have since been dropped.
The trial has been repeatedly delayed since then.
The jurors in the Chicago court case were selected from an initial pool of 150.
They include a man who spent five days in jail for marijuana possession and the wife of a Baptist preacher.
On Friday, Judge Vincent Gaughan refused a media request for access to transcripts of any parts of the hearing held behind closed doors.
He also refused to lift a gagging order forbidding lawyers from talking about the case.
The judge said he was not trying to inhibit the press but wanted to guarantee a fair trial.