Why are object descriptors streamed?
Indeed, one may argue that all the elementary streams for a presentation are known at the start of that presentation. However, anticipating highly dynamic content, MPEG found it prudent to allow for half-way updates of the set of object descriptors, to cope with newly appearing content streams. And therefore the notion of an ‘elementary stream’ was applied to the object descriptors as well, same as to all the content elementary streams.
