Opportunistic Data

Opportunistic data allows operators to maximise the usage of available bandwidth through the management of private data alongside DVB subtitles. This innovative approach ensures that bandwidth allocation can be fully optimised at all times whilst ensuring the secure delivery of subtitles.

Opportunistic data is the term used to describe additional data that is added to a compressed video stream when there is space available. The bandwidth required to delivery a complete program with all its components varies from instant to instant. However, the delivery methods available, satellite, cable or wireless, provide a fixed bandwidth `pipe' so at any instant there may be some data space available that is not required for the video, audio or subtitles. At this point other data can be inserted. It is not possible to predict in advance when and how much capacity will be available data is inserted when the opportunity arises, hence the term opportunistic data.

Subtitle data is a good example of bursty data. For normal DVB bitmap subtitles a peak bandwidth of 80Kb/s is required to ensure the timely delivery of subtitles. However, as subtitles are only sent every few seconds the 80Kb/s bandwidth is not used all the time and the average bandwidth can be as low as a few kilo bits per second. It is important the subtitles are delivered on time therefore they must take priority but the rest of the time other data can be sent in the unused bandwidth.

In a multiplex with several channels, each with several languages of subtitles, the available bandwidth can be significant. For example, in a service with four video services, each with 4 subtitle languages, there will be 16 x 70Kb/s = 1.12Mb/s available, on average.

Target applications:

· Advert insertion clip delivery
· Set top box software updates
· Unicast web pages
· In advance PVR video delivery (Push VOD)
· Extra bandwidth for data services

The Polistream system offers the ideal solution for inserting opportunistic data. For more information contact us.