Robin Thicke takes the stand, plays keyboard in court during 'Blurred Lines' trial

LOS ANGELES (KABC) -- R&B star Robin Thicke took the stand and even played the keyboard in court in a copyright infringement lawsuit brought on by the family of Marvin Gaye over the smash hit, "Blurred Lines."

There was no red carpet for stars Thicke and Pharrell Williams as they arrived at the federal courthouse.

Their appearance in court Wednesday was commanded by a lawsuit. They are accused of a musical rip-off. Their hit "Blurred Lines" sounds too much like Gaye's song, "Got to Give it Up" according to Gaye's family.

In court, the smiles the performers display in their music video vanished. The jury viewed clips of a sullen Williams, deflecting questions in a pre-recorded video deposition.

An off-camera attorney asked about the song's composition, "What are the names of these notes?"

Williams responds, "I am not comfortable with that."

The attorney tries again, "What is the duration of these notes?"

Again Williams responds, "I am not comfortable with that."

The performer repeated the same answer throughout the 14-minute deposition as the attorney tried to establish whether the R&B sensation could read music.

It is the composition, not the recorded song, that is at the heart of this dispute.

Jan Gaye, the wife of the deceased singer, testified that when the family heard "Blurred Lines," they praised it and tweeted out a thanks to Williams and Thicke thinking that the duo had paid a licensing fee for the use of "Got to Give It Up." The family learned later that no permission for use had been requested.

The widow testified that key elements of the 1977 hit and "Blurred Lines" are similar, including the bass line, keyboard harmonies, melodies, falsetto and lyrics.

But the singer's attorney showed her the lines side by side, showing the words and phrasing were different.

"I'm not seeing anything here. I guess I was mistaken," Gaye admitted.

Thicke took the stand and was challenged on statements to the media, where he spoke of Gaye's work as an inspiration. One interviewer had told him "Blurred Lines" sounded like "Got to Give it Up" Part Two. Thicke agreed in his pre-recorded deposition. Yet in court, he told the jury he didn't mean it.

"I was high and drunk every time I did an interview that year," he said.

He went on to say that Williams composed virtually the entire song.

About the songs' similarities, the judge allowed Thicke to pull out a keyboard and demonstrate.

Thicke played phrases from "With or Without You," "Forever Young," "Man in the Middle" and "Let It Be," showing how similar chord structures can blend easily.

Thicke testified that in composing, there is a difference between using an inspiration and making a copy.

Some experts believe that this case could have a resounding effect throughout the music industry.

"Artists have drawn upon the inspiration for their songs, listening to other songs," legal expert Alison Triessl told "Good Morning America." "They may not be able to do that anymore."

Thursday, the jury is expected to hear about emails, including one from a Universal executive who said that "Blurred Lines" was utterly based on "Got to Give It Up."

The trial began Tuesday and is expected to last for two weeks.

ABC News contributed to this report.