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Chapter 13. Profiling and Conformance: A... > Profiling and Conformance: Goals and...

13.1. Profiling and Conformance: Goals and Principles

The goal of defining profiles and levels is twofold. The first goal is to ensure interoperability. Implementations of a profile at a certain level result in a decoder that behaves in a predictable way. Content encoded (e.g., by a real-time encoder) or authored (e.g., for streaming from a server) for such a combination will work on any decoder implementation that conforms to that combination. The second goal is to allow conformance testing to take place.

In theory, it would be possible to signal, at the beginning of a communication, the tools that a decoder has on board, so that the server or encoder could use only these tools—and profiles wouldn't be necessary. There are a number of reasons why this does not work in practice. First, content often is pre-encoded, and you want to be 100% sure that all target decoders can consume it. In low-complexity devices (often communication terminals) users want to be sure that their terminals will be able to communicate, and not leave that to the chance that the tool sets overlap enough. Just “getting new tools online” is often impossible and cumbersome at best. Exchanging capabilities before exchanging content will at least incur unwanted delays and requires a bidirectional connection that does not always exist.


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