file extension MXF

File extension MXF description:

Object-based file format that wraps video, audio, and other bitstreams ("essences"), optimized for content interchange or archiving by creators and/or distributors, and intended for implementation in devices ranging from cameras and video recorders to computer systems. In effect, the format bundles the essences and what amounts to an "edit decision list" (data used by audio-visual content editing systems) in an unambiguous way that is essence-agnostic and metadata-aware.

Although the specification allows for complex, multipart objects, most commentators say "MXF should be seen as the 'digital equivalent of videotape,'" an allusion to videotape's simple, linear structure. See Notes for a comparison to MXF's supertype, AAF_1_1, which most commentators describe as "allowing for the expression of complex relationships between parts" and "wrapping all elements of a project for continued production or archiving." Essences are wrapped in containers, implementations of the MXF_GC (MXF Format Generic Container) for specific encodings. Essences are generally internal (within the MXF file); they may be external (and identified by reference), although this is discouraged. [Must external essences be in the same types of containers? Comments welcome.]

Tracks represent the passage of time. Timeline tracks (aka standard tracks) describe segments that butt against one another to form continuous sequences, event tracks may have overlapping events that refer to the point at which descriptive metadata is valid, while static tracks have no timeline--all of their descriptive metadata applies the entire duration of the linked essence track. Tracks are synchronized by putting them in a package (container for tracks).

The standard specifies a number of operational patterns ("OPs") intended to accommodate different levels of complexity in a file, e.g., one essence or multiple essences, "ganged" segments or a set of segments from which sub-segment are to be played, and so on. Application Specifications are specific profiles that are constrained to a certain OP, a particular encoding, metadata structure, etc. and other elements; see for example the MXF_AS-PBS under development by the Public Broadcasting System.