Definition: Video, audio, or other data essence that is external to the MXF file referencing them.

Description: This section looks at the linking and usage of external essence in MXF. The MXF specification is a bit light on normative text that defines how to use external essence, so this section is split into two parts (1) external essence contained in a separate MXF file, and (2) external essence in some other file type.

The one thing common to both external essence cases is the procedure to find the essence. Let s assume that there is a material package track that references a top-level file-package track with UMID U ₁ and TrackID T ₁. How do you locate the essence?

If there is an asset management, library, or content management system available, then this should be used to look up U1 and find the essence. Why? These systems are designed to manage and track live information, whereas any information stored in the file is old and possibly out-of-date location information. The unique reference to the file package is the UMID U ₁. Once the value of U ₁ is allocated, it is forever associated with that version of the essence, whether it is located inside or outside the file with the material package. A worked example of finding and synchronizing external essence is presented in the audio Chapter 6.

If no such system is available and there is no file package in the MXF...