Differences from the Data Stream Model

Object streams are related to simple data streams because both models use the idea of media elements travelling through a set of sources, intermediate processing objects, and sinks. However, in the object-stream model, the elements passed on are first-class objects, whereas in the data-stream model mere pieces of memory are communicated. Such a media element object hides the memory chunk, which contains the media data and which is the basis of the internal state of the object, by offering higher-level abstractions to the processing objects.

It seems advisable to divide the abstractions and functionality between the media element classes on the one hand and the sink and source classes on the other hand according to the following rules:

• The media element classes should at least restrict access to an object's media data by allowing access only through accessor methods.
• If the encoding of the media element contains any information about the element that is useful to processing objects and that is independent of the element's media type, the element object should extract this information from the memory chunk and should make it available to processing objects through appropriate accessor methods. Such information could comprise sequence numbers timestamps, or the size of the memory chunk.
• The media element objects might also contain part of the display, persistence, transport, or synchronisation functionality. The task of presentation objects would then consist of the coordinated invocation of the synchronisation or presentation methods of the media element objects.