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How to Preserve

Interoperable Master Format (IMF)

The Interoperable Master Format (IMF) has proved to be imperative in the exchange and processing of multiple content versions of finished works for a variety of global distribution channels, whether it be airline edits of films and television series, special editions or multiple language versions. But the IMF, and the Society of Motion Picture and Television Engineers' (SMPTE) suite of standards within, may be able to extended to support archival and preservation concerns as well. It could, for example, be used on the edge of an archive system, i.e. as a means of exchanging content in and out of the system. Or it could be used longer-term within the system as a storage format itself, splitting the component parts of an audio-visual master and maintaining them as a digital inventory. What does the forum think of the possibilities, and how the framework's core features could be wrangled for this broader usage?

The IMF is first and foremost a framework. This framework provides a mechanism to:

  •  Reference high-quality file-based masters
  •  Maintain components wrapped as track files
    •  Essence (image and audio)
    •  Data essence (subtitles and captioning)
  • Have a non-destructive means of combining track files via an edit-decision list through the Composition Play List (CPL), enabling rendition versioning
  • Have a means of specifying output renders (using static and dynamic metadata through the Output Profile List)
  • Enable packaging
  • Provide security

This framework enables assembly of the components into a nicely wrapped package for delivery, the IMP (Interoperable Master Package). However, the framework does not mandate packaging, and the framework may be used for keeping assets in situ.

The IMF rose from a desire to contain the version explosion in theatrical workflows, but is by no means restricted to theatrical workflows. In fact, numerous broadcast facilities are currently considering adopting IMF. The diagram below provides a conceptual flow of assets along the digital supply chain

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The immediate focus of IMF was distribution servicing. To enable this, the motion picture studios gathered under the auspices of the Entertainment Technology Center at the University of Southern California to develop a requirements specification. This specification was then submitted to the Society of Motion Picture and Television Engineers (SMPTE) to develop a set of standards that would enable manufacturers to develop products to support this initiative.

An overview of IMF by an IMF user group can be found at IMF Explainer.

A guide to the SMPTE suite of IMF standards is available at SMPTE OV 2067-0:2017.  The “Core Constraints” standard, which specifies provisions common to all IMF “Applications,” is available at ST 2067-2:2020 - SMPTE Standard - Interoperable Master Format — Core Constraints.

The IMF is fundamentally extensible, and can be readily extended with new kinds of audio-visual essence and metadata. Such extensions can be standard or user-specific. In fact, SMPTE continuously updates the IMF family of standards to match emerging use cases and fix bugs. Therefore, one consideration for the Academy Digital Preservation Forum is in what ways IMF can be extended to support archival and preservation needs.

The Forum solicits discussion around this area, and would be interested in hearing from you on how capabilities of IMF can be extended for archiving and preservation. For some thoughts on this, see Why IMF for archival applications?.

Keep in mind the core features of the framework, namely:

  1. Ability to reference original high-quality masters
  2. Provide non-destructive means of combining masters, with an edit-decision list
  3. Provide non-destructive means of modifying (that is, rendering) the content through processing instructions, to generate any deliverable, such as:
    1. a VFX render – based on render instructions that are codified within the OPL
    2. a color-correction render – based on CC lists or an ACES Metadata File
    3. a pan-and-scan deliverable – based on ongoing work by the ASC Framing Decision List

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  • Avatar for jun_jazz

    Questions I would be eager to know answers to are whether
    a) A componentized framework is consistent with the notion of Archiving Image and Audio ?
    b) Since we can store uncompressed assets within IMF - what are the additional archivist’s needs ?

  • Avatar for annie.chang

    I am also interested in the answers to Arjun’s questions. IMF was created originally for one purpose (distribution mastering and dealing with the infinite versions of a master), but that doesn’t mean that it can’t be extended for other uses such as archiving. Typically, we’ve archived image separate from audio, but that can cause issues when you are trying to bring that all back online in an approved manner. An IMF version of the original source material could be useful, but the downside is that there is some post processing needed to assemble everything unless there is a way to re-use CPLs from either downstream DCPs or IMFs.