Several television engineers have said that the move to digital television has turned stations into “bit managers, not broadcasters,” as they balance the multiple services—HDTV, multicast channels, data and perhaps even mobile TV—that can be offered within the 19.4 megabit per second (Mbps) payload of their digital spectrum.
One broadcasting entity that's already a full-time “bit manager” is Ion Media Networks, which carries multiple standard-def program streams on each of its 60 owned-and-operated stations and has promoted using the DTV spectrum to launch mobile TV services. Last month, Ion announced that it would convert its three program networks, Ion Television, Qubo and Ion Life, to HD in 2009. But they won't all be carried in hi-def by Ion stations.
That's because even though Ion is using the compression-friendly 720-line-progressive scan (720p) HD format instead of 1080-line-interlace (1080i), there is no way it can fit three HD streams, as well as the standard-def Worship Network program feed, in 19.4 Mbps and achieve even reasonable picture quality. So Ion will instead launch its flagship Ion Television network in HD beginning in the first quarter of 2009, while continuing to broadcast Qubo and Ion Life, as well as Worship, in 480-line-interlace (480i) standard-definition.
The plan for Qubo and Ion Life is to provide HD versions of them via satellite distribution that could be carried by cable, satellite and telco operators, says John Lawson, Ion executive VP of policy and strategic initiatives. Though the two networks have received scant carriage with multichannel operators to date, Ion's hope is that converting them to HD will make them more attractive.
“Given that satellite and cable providers are in a race to provide HD, the great thing about Qubo is that all the animation content is HD-ready,” Lawson says. “We have a ready-made HD kids' service that can be offered later in the year.”
Ion's goal is to roll out Ion Television in HD to its top 20 markets by Feb. 17, 2009, when high-powered analog broadcasts are scheduled to cease, and deploy HD across the rest of its stations by year-end. Ion is shopping for new HD encoders to deploy at both its stations and its network operations center in Clearwater, Fla. It currently uses a mix of Harmonic encoders and Harris splicing and monitoring gear to deliver pre-compressed MPEG-2 feeds to its 60 stations, and that process will continue after Ion Television goes HD, says Ion President of Engineering David Glenn.
Glenn is confident that Ion will be able to deliver one HD and three SD feeds while maintaining good image quality by using statistical multiplexing technology, which dynamically allocates bits to different feeds depending on the changing requirements of individual video frames on each service. Ion constantly monitors the bitrate allocations on its services today, and Glenn says it's not uncommon to see SD feeds drop to as low as 1 Mbps during static scenes. Hi-def 720p video could possibly drop to as low as 3 Mbps in the same scenario, says Glenn, who notes that encoder manufacturers have already demonstrated two 720p HDs and one SD service running in 19.4 Mbps.
“You have to manage the bandwidth, there is no question about it,” Glenn says. “What Ion has in its favor is that we're buying the latest state-of-the-art encoders, and we already have a state-of-the-art system to monitor them. Technology is on our side.”
Whether Ion could do an HD stream, three SDs and still have space for potential mobile DTV services is another matter. But Lawson says the decision to launch Ion Television in HD doesn't mean that Ion has changed its mind about the potential of mobile DTV.
As he puts it: “Those are business decisions that we'll make as the opportunities and requirements become clearer.”
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