BBC shifts some HD transmissions to 1080p...

...troubling some Sony TVs in the process

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Updated The BBC has quietly begun broadcasting HD content in 1080p, sort of.

Since April, some BBC HD transmissions over Freeview HD have combined 1080i and 1080p material, switching between the two on a GOP (Group of Pictures) by GOP basis.

A GOP is a batch of H.264 encoded frames combining an initial, reference picture followed by a sequence of partial pictures that store the changes that need to be made to the first frame to generate the remaining frames in the GOP video sequence.

The reason for the switch to mixed 1080i/1080p: that's the way many HD shows are produced, combining 1080p material shot on location, with transitions and credits recorded and rendered in 1080i so they run more smoothly. Studio material is shot in 1080i too.

Matching what's displayed with what's produced - rather than re-encoding everything at 1080i - makes for a better quality picture, say BBC engineers. Provided, of course, your set-top box outputs at 1080p.

All good stuff, but it's causing some viewers woes. Owners of recent Sony HD TVs, for example, have complained about audio drop-outs, presumably as the tellies' integrated tuner-fed decoders temporarily lose track of the audio while juggling the switch from 1080i to 1080p and vice versa.

Sony said yesterday that it's working on a solution, and promised more information on 7-10 days. The BBC likewise told What Hi-Fi that it will work with any vendor suffering from such problems to help sort them out.

Perhaps it should have done that at the start, running the new approach to transmission by TV makers first in order to prevent the problems Sony owners - and possibly those with other telly brands too - have experienced.

The BBC subsequently told us it "worked closely with receiver manufacturers ahead of these changes to investigate any interoperability issues". Even so, at least one vendor's customers are still suffering.

While the Freeview HD spec for set-top boxes mandates handling 1080p material at 50 frames per second, to cope with this kind of thing, that doesn't appear to be the case with tuner-equipped TVs which is why Sony's sets - among the first in the UK to ship with on-board Freeview HD tuners - are now being bitten by the BBC's change.

Don't forget that, depending on the size of your TV, 1080p transmission may not actually matter much. ®

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