Obama Ad will have live portion - Bill Clinton may join him on stage!

Barack Obama has got a half-hour of primetime TV on CBS and NBC, sources confirm.

The Obama promotion is producing a nationwide pitch to voters that will air on as a minimum two broadcast networks. The ad will run Wednesday, Oct. 29, at 8 p.m. - less than a week previous to the general election.

UPDATED: Wednesday night's Barack Obama primetime ad will contain a live segment near the end of the telecast.

The Democratic candidate is in Florida tomorrow and teaming with former president Bill Clinton for the first time on the campaign trail. The live portion will be broadcast from an evening rally, though it's not clear if Clinton will share the stage during the segment.

"The entire half hour is being fed live to various outlets from a site in Florida," a source said. "They'll be feeding a tape for most of the broadcast and then a live portion at the end."

Though going live is technically more challenging and potentially more risky for Obama should something go awry, the plan will likely result in higher viewership than a mere taped telecast. The move also further explains why the Obama camp insisted on having all its ads run during the same time period.

The special -- titled "Barack Obama: American Stories" -- marks the first time in 16 years a presidential candidate has purchased a national address before the general election.

The telecast should provide a unique test of the electorate's current interest in Obama's messaging. Campaign ads, after all, are typically considered a nuisance best avoided rather than Must See TV -- especially in swing states, which have been bombarded with every flavor of political advertising in recent weeks.

But given the heavy interest in the election in general -- with convention speeches and the debates managing to set Nielsen ratings records -- curiosity tune-in could be high. NBC, CBS, Fox, MSNBC and Univision are among the best known outlets carrying the telecast.

Ratings for paid programming are often not released to the public, and Nielsen was still mulling on Tuesday whether to announce the ad's viewership. Given the heavy media interest, a release seems likely.

Update: The Obama campaign provided The New York Times with a trailer from the taped portion. The footage is described as--

"...heavy in strings, flags, presidential imagery and some Americana filmed by Davis Guggenheim, whose father was the campaign documentarian of Robert F. Kennedy. As the screen flashes scenes of suburban lawns, a freight train and Mr. Obama seated at a kitchen table with a group of white, apparently working-class voters, Mr. Obama says: “We’ve seen over the last eight years how decisions by a president can have a profound effect on the course of history and on American lives; much that’s wrong with our country goes back even farther than that.”

The Times added that the content will highlight the stories of four American families and the challenges they face.