The road to multichannel broadcasting

The multichannel technology genie is out of the bottle and the pressure is on broadcasters to establish new channels, re-purpose valuable content and achieve additional revenue through advertising, subscriptions and new interactive services.

The potential for cost savings is considerable. Repeat fees due on existing programs are, obviously, considerably cheaper than new production budgets when it comes to filling extra schedules. And those multichannel schedules can be planned in such detail and so far in advance that very small numbers of people are needed to supervise them to air with very little manual intervention. Another advantage of the multichannel approach for broadcasters is that it can give them the appearance of offering many more programs than they deliver in reality.

With so many channels and so much crossover of material, it is important that broadcasters retain a distinct and crowd-pleasing identity, while saving money. A crafted, professional presentation style is essential, particularly among services that are providing very similar content. Broadcasters get around this by crafting the output with complex junctions during the day, while leaving the content to run on ‘automatic pilot’ overnight with fewer finishing touches and one operator looking after, say, ten or twelve channels without too much intervention.

Bringing together the origination of multiple channels under one roof into a single playout center can create even greater economies, and this is where automation systems can make a difference.

The OmniBus Colossus delivery system for example, gives an operator responsibility for large numbers of channels, from one to several hundred, and a timeline-based display provides a quick and immediate overview of those channels along with any specific problems in terms of missing media or failed devices. More a stream-delivery system than an automation system, it has been designed to deal with not just the conventional push-model TV playout, but also VOD and NVOD applications as well as the playout of radio material and the streaming of media to the Internet.

Other technological issues to be taken into consideration include video compression and the multiplexing to different transmission paths. A signal must be compressed by at least twenty times to fit within the available ‘pipeline’ because of the amount of data it contains due to changes in movement and contrast in the picture. The real key to multichannel operations is that the capacity of that ‘pipeline’ is finite, but the number of channels expected to fit in it is not.

In order to get more channels down the pipeline, the amount of data used to convey the information has to be reduced. The most important technique to achieve this is coding efficiency and this depends on video and audio signals containing substantial amounts of redundancy.

Television and sound signals have two major constituent parts - those that are novel and unpredictable (the entropy) and those that can be anticipated that are redundant. Compression systems work by ensuring these two are separated and that – mostly - just the entropy is transmitted.

The most widely used technique is MPEG2 which enables a digital broadcast signal that normally needs more than 200 Mbps to be compressed into a bit rate providing an acceptable quality of broadcasting of between three-and-a-half and six Mbps.

The information contained in successive fields normally only changes by a small percentage. Clever analysis techniques of the signal can provide a paradigm of the image together with the predictive fields. This is known at the group of pictures (GOP). A typical GOP is 14 fields long - just one in 14 is an actual time sample. Fields in between are estimated and predicted.

The advantage of compression is, of course, a massive saving in bit rate that enables several information channels to pass down one normal sized path. The disadvantage is that the predictive and estimated process does fall down if there are fast changes between successive fields such as in sport or light entertainment.

The effect is that the decoders cannot satisfactorily predict the fast change in images and the picture breaks up into random blocks of light and colour until the decoder can catch up.

In addition to the long GOP compression process, another method is that groups of channels are multiplexed together into a single bitstream and the available bandwidth on the stream is dynamically allocated to the channel that requires the most bit rate. This is statistical multiplexing or stat mux.

The coding and compression techniques are the same for cable and satellite broadcasting but there is an inherent limit on the bandwidth available on a single cable system. The digital satellite route can, however, be expanded by the addition of extra satellites.

There is, therefore, no practical upper limit to the number of channels that can be delivered to viewers but there are obviously cost issues surrounding the launch and maintenance of extra satellites.

Broadcasters have had to look to other media such as digital satellite or cable and have turned to compressing signals over an analogue carrier as in the case of DVB-T digital terrestrial broadcasting. DVB-T overcomes the inherent distortion of the signal due to the analogue carrier, makes it more robust, and provides acceptable digital quality for the viewer but with some reduction in picture quality.

Solutions providers have a major role to play in assisting with the movement of content as well as storing it as quickly and efficiently as possible. Good server management ensures that material is always readily available while content that is not needed immediately can be placed in a near-line store. All this is carried out without the involvement of operators.

High levels of automation are also required - not just to keep costs down, but to also take advantage of new services such as electronic program guides (EPGs) that allow viewers the luxury of building their own viewing and recording profiles. To an automation provider, EPGs are complicated because they are sent at regular intervals and are constantly being updated via set-top boxes. They must also be synchronized with the web presence so that all relevant marketing opportunities and promotions relevant to each program are kept up-to-date.

At an industry level, the key to a new wave of consumers is deregulation of the airwaves and networks. The current rules may well prevent the rise of all-conquering monopolies but they are also preventing innovative media companies from implementing new ideas because they cannot test them on ‘real’ viewers. Another change we will see is increased pressure on mainstream broadcasters because of the niche services offered by multichannel. It will keep them on their toes and more responsive to their customers’ needs.

Andrew Dicks Reich’s is a sales consultant with OmniBus.