Multimedia Document Handling — A Survey of Concepts and Methods

ions ([AGH90]) A physical device (PDev) is a hardware device which is able to generate or consume continuous media data, such as a microphone, camera, etc. Logical devices (LDevs) represent virtual CM I/O devices dealing with exactly one continuous media stream, referred to as a strand. Multiple logical devices may be multiplexed onto one physical device or be connected to many physical devices. The former is the case, for example, for multiple audio streams (Ldevs), which are output (mixed) onto the same loudspeaker (Pdev), while the latter could mean that the same audio stream is output on several loudspeakers. Composite logical devices (CLDevs) represent the source or sink of data on a particular continuous media (CM) connection carrying multiple streams (strands) composed into a CM rope. A rope represents an interleaved structure carrying the data units of the single strands. Ropes are only exchanged between CLDevs. Each CLDev is mapped on (associated with) a number of LDevs sending or receiving the ropes. Logical time systems (LTS) are used to drive the timing of CLDevs. An LTS provides a temporal coordinate system by which the synchronized input or output of several ropes is controlled. End-to-end connections are set up by creating a CM connection to the ACME server, creating the involved LDevs and CLDevs, mapping the LDevs to the desired PDevs and the CLDevs to the desired set of LDevs. Each CLDev is finally associated with an LTS. Starting the LTS results in starting the synchronized I/O of the ropes of the associated CLDevs.