It is a data object used as part of a presentation
Media items can be monomedium (single medium i.e. text or
sound) or composite (interlieved video and sound)
Media items have data-type dependent properties such as,
Most important property is in relation to time and space.
text or graphics-spatial, no intrinsic temporal dimension
video or animation- spatial and temporal dimensions
sound-temporal But no spatial dimension
Media items does not have to be a complete file or object
it can be reference to part of a physically stored object.
For
example: in case of text the object may be a complete object, where only a
section is used. In case of sound, a selection from a music item that
last few seconds.
Other media items that can be
included in a presentation are outputs
from external processes (real time sources) such as,
a video camera pointing at a
scene
outside, or reading from a monitoring device. We can still treat these as
objects with similar space dimensions, but they have indefinite time
dimensions.