09.00 Update: Last August’s move by BBC HD to a new generation of encoders for its satellite service has resulted in a series of criticisms from some viewers over the quality of its pictures. In a news conference for the technical launch of BBC HD as a terrestrial service Graham Plumb, acting controller distribution, BBC Operations Group compared the problem to earlier issues with the amount of bandwidth allocated to digital radio channels. People were, he believed, focusing on the fact the number had got smaller, rather than the improved processing power of the codecs. “I think unfortunately what has happens is a little like in digital radio, people tend to equate the bitrate with the quality and find it very difficult to believe you can get an improved generation of coder you can actually use a smaller bitrate and still achieve the same level of quality”.
When BBC HD was originally launched in the spring of 2006, the channel was running at 19 Mbps, following a coder software update it moved to 16 Mbps, a hardware encoder installation later taking speeds down to 9.5 Mbps. All of the movements can be said to be in line with industry best practice.
Plumb acknowledged there had been some initial difficulties with the first generation of encoder, which had been quickly owned up to. “There was a very small issue on certain shot changes and that has been cleared and won’t be an issue with Freeview HD whatsoever,” he said. “I’ve been backwards and forwards to the Kingswood labs and compared the old coder with the new coder side by side and I have to say that the quality is as good if not better than with the original coder even though we’re running at that lower bitrate”.
On the new Freeview HD service launched today (Wednesday), statistical multiplexing will be used, as opposed to the fixed bitrate found on satellite. Plumb explained the DVB-T2 service would be set to a constant bitrate, ensuring that the amount of bandwidth would stay within a set level, and give a better experience overall.
