Kelly, who attended a pretrial hearing in Chicago yesterday but did not address the court, has pleaded not guilty to the charges. The 41-year-old faces up to 15 years in prison if convicted.
The Grammy-winning singer is glad the wait is over, his spokesman said.
"Every waking moment, he's always had this hanging over his head," he said. "He's confident that when all the evidence comes out he'll be shown not to be guilty of any crime".
Singer R. Kelly arrives in court for the first day of jury selection in his child pornography trial at the Cook County Criminal Courthouse in Chicago
Prosecutors claim the videotape was made between 1998 and late 2000, and that the girl was born in September 1984.
Kelly was indicted on pornography charges in 2002 after the tape surfaced and was sold illegally on the streets and the internet.
The centrepiece of the trial is likely to be the video footage, which Judge Vincent Gaughan ruled may be shown in open court.
However, even the alleged victim, now 23, says the girl in the video is not her.
"How is there not reasonable doubt when the two people say it's not them?" said one observer, Chicago lawyer Michael Helfand.
But Mr Helfand conceded that it is unclear what supporting evidence the prosecution might present.
Police and prosecutors said their investigation, including interviews with about 50 witnesses, prove Kelly and an under-age girl were on the tape, and that FBI forensics experts had determined the tape was authentic.
News organisations have moved for the right to see sealed court records and transcripts.
Judge Vincent Gaughan said at yesterday's hearing he would not issue a ruling on that until next Friday.
Prosecutors and Kelly's defence lawyers oppose media access because, they say, a news frenzy will make it harder to pick jurors and to guarantee their impartiality during the trial.
Kelly has settled three lawsuits accusing him of having sex with under-age girls, filed in 1997, 2001 and 2002.
In the third, the woman claimed that she began having sex with Kelly when she was 16, and that he forced her to have an abortion.
In 2003, Kelly was arrested in Florida on child pornography charges after investigators said they found photos of him having sex with a girl. Charges were dropped after a judge ruled that detectives had illegally seized the photographs from a digital camera in his home.
Documents show Kelly secretly married the singer Aaliyah in 1994, when she was 15. The marriage was later annulled by her parents; Aaliyah died in a plane crash in 2001.
The trial is expected to last several weeks.
