BBC report recommends lowering picture quality on Freeview

A report by Deloitte for the BBC Trust into efficiency of spectrum use has stated that, in addition to more efficient coding and multiplexing, changes in modulation from 16QAM to 64QAM and future adoption of new technologies such as DVB-T2 and MPEG-4, efficiency improvements in the BBCs Freeview multiplexes over the next five years can also be achieved by reductions in the picture quality of servies.
The report considers reducing the capacity used by individual channels by increasing GOP length and reducing picture resolution to three-quarter screen or less to increase the number of services that can be accomodated within a multiplex. They acknowledge that lower picture resolution will generally look softer as fine detail might be lost. The BBC currently broadcasts BBC1,2,3,4,CBBC,Cbeebies and BBC News24 in full resolution, whereas ITV and Channel 4 only broadcast their primary channels, ITV1 and Channel4, at full resolution. A longer GOP length will increase channel switching times because the decoder must wait longer for the next complete picture frame. The PSB multiplexes (1,B,2) currently use the shortest GOP length, while commercial multiplexes (A,C,D) use higher variable GOP lengths. The report notes that channels on the BBCs Mux1 require at least a third more capacity than channels on other multiplexes. The higher video bit rates on Mux1 are a result of older coding technology, less extensive use of statistical multiplexing (BBC1 is currently excluded from statistical multiplexing due to regional variations) and choices regarding picture resolution and GOP length. The report recommends reducing picture resolution on BBC3 and 4, CBBC, Cbeebies and BBC News24 to 3/4 screen, and varying GOP length from 12 to 36 frames.

The planning process that existed prior to 2007 for the use of spectrum capacity reflected a situation where the BBC had sufficient capacity available for the services that it wished to provide. However, in recent years both the BBC’s and third parties’ service demands have increased. In addition to the BBC’s aspirations to provide HD, several public service broadcasters, including five, S4C and TG4, are expected to be directed by the Secretary of State to be carried in BBC multiplex capacity. The BBC appreciates that available capacity may no longer be sufficient to cover their service aspirations, and therefore the importance of using the spectrum efficiently and effectively. The report recommends that in order to increase viewer value, the BBC needs to consider its service prioritisation, for example by accommodating HD services which the public appear to value highly.

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