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Statistical multiplexing, efficient encoding key to WRAL multicast

Two and a half years after WRAL in Raleigh-Durham, N.C., began multicasting a 24-hour local news channel, the operation is going strong and the station is pleased with the quality of its transmission, said programming and special projects manager Jimmy Goodmon Jr.

WRAL launched NewsChannel on its SD multicast channel in August 2001. Thanks to statistical multiplexing and efficient encoding, the station is pleased with the image quality of the SD NewsChannel and WRAL’s HD broadcast. Photo courtesy WRAL-TV.

The station, which pioneered digital broadcasting seven and a half years ago, split its digital bandwidth allotment into an HD channel, an SD channel and a 1- to 1.5-Mb/s channel for datacasting. Bandwidth is dynamically assigned to the channels as needed through statistical multiplexing. This along with efficient encoding maintains optimum picture quality on the SD and HD channels.

“The picture WRAL delivers using statistical multiplexing and efficiency of encoding is superb,” said Goodmon. “We can deliver HD and SD with no degradation, and we expect to see 10- to 15-percent improvement in the encoding process every year. We are happy now and know where we are going.”

“We utilize statistical multiplexing, which has been described by some in the industry as being like dumping water into the bucket that needs it,” Goodmon explained. “There is a bit of a controversy in the industry over bit starving versus not bit starving. But our picture looks great.”

WRAL uses the 1 to 1.5 Mb/s devoted to datacasting for a variety of offerings, including distribution of game software, short movies, a 380Kbps edition of WRAL’s 6 p.m. news, live streamed news from the NewsChannel, an abridged version of and even a locally originated game show called “Brain Game.”

“This is program content that we couldn’t deliver before,” said Goodmon.

While the station does not know how much larger its datacast audience is than its initial test market of 100, the station is expecting big things from datacasting in the future.

“We have been experimenting with ideas that will be great for the future -approaches that are not interactive per se but send information out that can be stored in the memory of the users’ computers that they can access as desired,” he said.

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