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Resources: Carousel lengths

The load time for your DSat application is strongly determined by the carousel length, especially for simple applications or on newer STBs. This ready reckoner will help you get a handle on your carousel lengths at the start of a project.

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Carousel lengths are only a good guide to broadcast resource download latencies when carousels are reliably played in full; from time to time, when your data is being multiplexed with other streams, that may not be the case. Long and ‘lumpy’ load times can be the result.

To identify issues such as these, one can include a signal module at the end of any static carousel that’s delivered for playout; your application can then monitor how often, and how regularly, the signal module is seen.

Directly-measured carousel lengths can then be compared against observed latencies for modules throughout the carousel.

Carousel length ready reckoner

These carousel lengths are in seconds, for a given payload size and broadcast bandwidth. Don’t forget that the usable payload will be a few percent smaller, due to overheads in assembling the flow and mux files. There’s also some evidence that there’s a limit to how high you can turn the effective bandwidth whilst still improving load times on the very oldest STBs.