There was a time when live concerts were a staple of broadcast television. American Bandstand was on the air for 37 years, and seemingly every town with a TV station and access to a gymnasium had a local version. There was even a time when MTV would beam out performances by bands big and small, produced by a professional crew of cameramen, sound engineers and set designers.

Amateur recordings of amateur musicians abound on the web, but for music fans who like concerts without a panel of judges enthroned between the audience and the band, choices have been shrinking.

But there is at least one stage left where the technical engineers behind the mics and cameras are as talented as the people on the stage. Over the last 20 years, the Late Show with David Letterman has become one of the last, best places to see a live musical performance without getting up from your couch. Every show since Billy Joel played opening in 1993, has been brought to you by members of New York Local 1212.

"I don't even know how many concerts we've done. Even the great ones, there are too many to count," said Dan Campbell, Emmy-award winning camera operator for the Late Show. "I've been at CBS for 32 years and some of the cameramen have been here longer than me."

Musical goliaths and bands on the make alike have made the journey to the Ed Sullivan Theater on Broadway, and played to millions. The downside, of course, is that the bands usually come on last, after the host's inimitable interviews with celebrity and not-so-celebrity guests. Appearances are brief, often just a single song.

So in 2009 CBS Interactive launched Live on Letterman, webcasts of extended performances by musicians who appear on the show.

Over the last five years, the show has hosted more than 70 Live on Letterman concerts, often featuring bands that haven't played a venue as intimate as the 460-seat theater in decades, including U2, Kiss, Foo Fighters and Taylor Swift. The famous stage has also hosted less well-known and cult favorites like Band of Horses, the Shins and Wilco. According to CBS, more than 185 million people have watched the webcasts, either live or on-demand.

"These productions are a perfect demonstration of the versatility and expertise of our IBEW technical engineers," said Local 1212 Business Manager Ralph Avigliano. "And the audience they draw are proof that I'm not the only one who thinks our members are the best there is."

Producing the webcast requires a complete transformation of the set twice in one day. During the show, Letterman and his desk are front and center and the musicians play downstage and to the side. For the concerts, stagehands strip the stage bare, shuffle the desk into the wings and plant the band at the very edge of the stage, almost beneath the audience in the balcony.

Then the IBEW technicians are unleashed, hustling the production consoles offstage and then deploying an armada of cameras and microphones.

"We put cameras out in the audience, on booms and these little POV [point-of-view] cameras — we call them weasel cameras — all over the place: on the drum set, the keyboards, anywhere the director wants," Campbell said. "Then we make sure they are up and running and operate them during the show."

Campbell's favorite moments include the duet between the rapper Snoop Dogg and Willie Nelson, the time they set up Paul McCartney to play on the theater marquis out on Broadway and the recent show from Foo Fighters.

"Concerts last 45 minutes usually, but they played two hours. The first hour, we mimicked the old Ed Sullivan set, they dressed like the Beatles and we broadcast in black and white," Campbell said. "The second hour, we switched to color and they blew the roof off."