Freeview Red Button Opening Ceremony coverage downgraded to audio only

The BBC's Director of London 2012, Roger Mosey, has today confirmed it will not be possible to offer a full service on Freeview's BBC Red Button 301 during next Friday's Opening Ceremony.

Red Button 301 was supposed to show the Opening Ceremony with a "no commentary" and an "audio description" option, in addition to BBC One showing the same event with standard commentary. The BBC News Channel would also be simulcasting the Ceremony, possibly with the addition of the BBC News ticker. This would have meant three services on the same Freeview multiplex carrying the same pictures at the same time, having the same bandwidth requirements.

In his latest blog post, Roger Mosey confirms that when multiple channels show the same content at the same time, "TV platforms can struggle and go "blocky"  - especially when the pictures have a lot of activity in them." 

The situation is worse when there is little surplus capacity available on the multiplex. Due to data and radio services (and in Scotland, BBC Alba), there is very little spare room left on Freeview for when multiple services all need lots of bandwidth at the same time.

As a result, the BBC will offer Red Button 301 as an audio only service, carrying audio description - also known as "AD", a special service for the blind and partially-sighted that inserts additional descriptive narration to events on screen.

The Opening Ceremony will still be available in sound and picture on BBC One, which will have its picture quality protected, according to Roger Mosey.

 "We know this will disappoint some people, and we've tried really hard to find a solution. But we have to follow this course to protect the picture quality on BBC One where the overwhelming majority will be watching", he said, concluding his blogpost.

  • Update: It is not known what is to happen with the HD simulcast of Red Button 301 on Freeview HD channel 304. As BBC One HD will be carrying the Ceremony, it would make sense to close the HD red button version too, as this would also preserve bandwidth.


ANALYSIS
The problem described today by Roger Mosey is actually nothing new, and "macro blocking" has long frustrated viewers of ITV1 and Channel 5, who have been frequently criticised on internet forums for poor picture quality, as commercial broadcasters have often packed terrestrial multiplexes and satellite transponders with little leeway for spikes in bandwidth demand. 

With regards the Opening Ceremony issues - this is due to the difficulties of transmitting the same pictures at the same time on several channels on the same multiplex. The less spare capacity that it available on a digital multiplex, or even a satellite transponder, the harder it becomes. This is because most digitial terrestrial and satellite services are "stat muxed" - i.e. there is an amount of bandwidth for several TV channels and different channels take a different share of the bandwidth depending on what is being broadcast. Each channel will have a variable bitrate that can increase/decrease from one second to the next.

So, if BBC One is broadcasting a fast moving sports event, it needs more bandwidth, but if BBC Four is showing a slow moving documentary on the life of Beethoven, it will need less bandwidth, so one service would take from the other - BBC One's bitrate would increase, BBC Four's would decrease. If several channels are all broadcasting the same thing at the same time, and the demand on bandwidth is great (because there's a lot happening on the screen), there's a crunch and the pictures go blocky - there's no spare bandwidth to borrow from somewhere else.

On satellite, the BBC and ITV have to spread their regional variants out over several transponders due to this risk, as you could have several identical versions of the same channel (outside of regional programming) all with the same peaks and troughs in bandwidth usage. As it's not cost-efficient to spread the content over too many transponders, there will still be several identical versions on the same transponder. As a result, transponders may not be as tightly packed with services as they could be. Sometimes, a brief time delay is added on some regional streams to ensure that the "peaks" in bandwidth requirement don't happen at exactly the same time.


COMMENT
Why not have a 128 kpbs audio channel added to BBC One, accessed via the red button for the no-commentary option (just the sounds of the event minus Huw Edwards), in the same way that additional audio options can be added to 301?
The same principle could be applied during football matches - now that switchover has brought BBC One and BBC 5 Live onto the same multiplex, it should be possible to provide the option for BBC One viewers to switch the audio to 5 Live via the red (or blue) button, without having to have the exact same match duplicated on 301 for the sole purpose of having multiple commentary options. If 301 can have multiple audio options added, so can any videostream on Freeview.
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