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BBC mulls BBC HD picture quality demos

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BBC mulls BBC HD picture quality demos
The BBC has revealed that it is currently evaluating staged technical demonstrations of BBC HD to alleviate the controversy around picture quality.

After new encoders were introduced by the BBC on August 5, the bitrate on BBC HD dropped from 16Mbs to 9.7Mbs, a reduction of nearly 40%. Viewers subsequently reported various issues with picture quality on the channel, and called for the broadcaster to return it to pre-August standards.

Speaking at the technical launch of Freeview HD, BBC acting controller of distribution Graham Plumb said that the corporation is "painfully aware" of the recent interest in its use of bandwidth and capacity on the HD channel.

Plumb accepted that "a few very vocal people" remain concerned about the picture quality of BBC HD on satellite. He explained that a major issue is that these people cannot see the results being produced in the BBC labs or the technical tests which have been conducted.

"I am thinking about that, because in terms of openness and transparency in what we do, I am trying to think of ways that we can demonstrate this to the public. Whether it's for the technies out there to see recordings of the new coder and the old coder - we could play them back-to-back so that people can actually see the things we are seeing," he said.

"But honestly, I promise you, I have looked at all the analysis and I think that largely it's people focusing on the fact that the number has got smaller."

Plumb claimed that a "vast" amount of work has been done in the BBC labs to test the technical quality of its HD output. However, he is aware that there remains a "lot of noise" on the subject.

"I think unfortunately what happens, a bit like digital radio, people tend to equate the bitrate with the quality. They find it very difficult to believe that when get an improved version of coder you can actually use a smaller bitrate and still achieve the same level of quality," he said.

"I have been backwards and forwards to the Kingswood labs comparing side-by-side the old coder and the new coder and I have to say that the quality is as good if not better than the original coder, even though we are at a lower bitrate."

Plumb accepted that an "internal glitch" occurred with the new encoder in the early stages which caused picture quality issues on "certain shot changes".

After publicly acknowledging the problem, the BBC has worked hard to address it. Plumb is therefore confident that there won't be any similar problems with the channel on Freeview HD.

The BBC is also changing the way it manages bitrates towards a new variable system which utilises all the statistical multiplexing capabilities of DVB-T2.

"On satellite, it's a fixed bitrate at the moment, just because of the way we were running the service, but we are moving to a variable bitrate service with all of the services statistically multiplexed in the DVB-T2 multiplex," Plumb said.

"We have maximised the picture quality we can receive from the service to ensure that it achieves a constant level of quality as managed by the coders, and so it doesn't shift up and down all the time. So I think that will give an even better experience for the consumer."

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