Metadata Exchange Formats

Metadata is used in film making for a number of different purposes.

Metadata is included in both video and audio recordings which identifies it in subsequent workflows, enabling it to be indexed and sorted along with a description of the contents. 
Metadata can arise in two ways. First, there is ‘technical’ metadata such as that created in a digital video or cinematography camera by the device – this could include the codec, frame rate, location via GPS etc. Secondly, there is ‘descriptive’ metadata created by the user either in production or subsequently further down the workflow.

Both types of metadata must be transferred, along with the asset it refers to, and is used in the production and post production workflows through to delivery and archive. There are different metadata formats in use and the descriptions below explore the most common formats found in production.

XMP (Extensible Metadata Platform) is based on open standards and uses the formal language of the Resource Description Framework (RDF). The aim is to store metadata from different applications in a uniform manner so that all the information is understood by subsequent software in the workflow chain. Adobe uses this standard in all its products. XMP is also used with Exif (Exchangeable image file format) for digital photography.

XML (Extensible Markup Language) is a very common markup language for the platform-independent exchange of information and data. The structure is simple and uses very small XML files that can be displayed in any browser or text editor. An advantage of using XML is that the information in it is both machine and human readable. (XML files are also editable, but care should be taken when making changes!) XML is logical and hierarchically organised in a tree structure. The format is used by the ARRI Alexa to communicate metadata in clips produced by the camera. Final Cut and Adobe use the format extensively in their projects and timelines to convey information about the video and audio data, as well as exchange information with other systems.

AAF (Advanced Authoring Format) is a powerful exchange format and widely used in post production. Implementations can be found in all major manufacturers like Autodesk, Digital Vision, Avid, Microsoft, Apple, Quantel, Assimilate and others. Entire projects including all structures, effects, tracks – as well as video and audio media in MXF format – can be exchanged using AAF. The range of functionality is limited only by the degree of implementation of the respective application. An AAF-based post production workflow can be highly efficient. One drawback is that AAF is not human-readable.

ALE (Avid Log Exchange) is a text-based metadata exchange format made by Avid . ALE is a type of log file that can subsequently maintain specific information within an Avid bin for master clips. Referencing of the information to the master clip uses timecode. ALE can be read with a text editor and can be edited. However, the formatting can often be very confusing if importing an ALE as a CSV file (Comma Separated Value) e.g. in Excel the contents are displayed in tabular form. When editing ALE files it should be noted that the tab-delimited format is mandatory. Furthermore, only specific ALE files can be edited although any kind of list or otherwise simple structured (text) data can be exchanged as a general CSV.

EDL (Edit Decision List) is a long-established form of metadata exchange format in post production and is both machine and human readable and can be edited as a text file. The EDL is, however, very limited in the scope of information that it can carry.

Work is underway by the IPTC, DPP and other partners to build more robust metadata into the production workflow, from camera to delivery.