The lengthy agreement is unprecedented, the Los Angeles Times said Monday.
Burns' projects include films on Prohibition and the the national parks system, Paula Kerger, PBS president and chief executive, said during the semi-annual meeting of the Television Critics Association.
Critics quizzed Kerger and PBS' chief content director John Boland about the length, timing and language of Burns' World War II documentary "The War."
The 14-hour series will air in mid-September, butting heads with commercial stations launching their new seasons. Boland said PBS won't be affected because the system does not rely on ratings and advertisements as commercial broadcast operations do.
In justifying the show's length, Kerger called the film Burns' greatest work.
"For him to do the subject justice and to tell the story well, it's the right length of time," she said.
Regarding the soldiers' frank language and whether the Federal Communications Commission will call it obscene, Kerger said any decision on editing the language would depend partly on the outcome of similar pending court cases.
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