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Interoperable Master Format

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Interoperable Master Format
Filename extension
.xml
Developed bySMPTE
Initial release29 August 2013; 11 years ago (2013-08-29)
Latest release
SMPTE ST 2067:2021
12 October 2020; 4 years ago (2020-10-12)
Type of formatContainer format
Container forAudiovisual material, rich metadata
Open format?Yes
Free format?Yes

Interoperable Master Format (IMF) is a container format for the digital delivery and storage of finished audio-visual masters, including movies, episodic content and advertisements.

In IMF, each kind of essence (video, audio, subtitles, etc.) is stored in individual media files (“Track Files”) and the instructions for synchronizing these media files are stored in a separate playlist file (“Composition Playlist”)[1]. This component-based approach allows the large media files to be reused across multiple playlists, each representing a different version of the content.[2].

The IMF family of standards is maintained by SMPTE.[3] Its first edition was published in 2013.

Architecture

At the heart of IMF is the Composition, illustrated in the first image, which consists of a single Composition Playlist and a collection of Track Files. Each Composition corresponds to a single audio-visual master.

An IMF Composition is defined by a Composition Play List
IMF Composition Example

Each Track File contains a single kind of essence corresponding to a single aspect of the presentation. For example, a first Track File might contain the primary video program while a second might contain Spanish stereo audio and a third English subtitles. Track Files use a constrained version of the MXF OP1a format Material Exchange Format[4]

The Composition Playlist is an XML document[5]. It assembles the Track Files[6] onto virtual tracks that are synchronized onto a timeline. It also contains metadata associated with that timeline.The combination of a Composition Playlist and the Track Files it references is called a Composition.

The primary benefit of separating the Composition Playlist from the Track Files is that a Track File can be reused across multiple Compositions as shown in the second image. Each Composition represents a different version of an audio-visual work. Since different versions of a title typically differ in small ways and this component-based approach results in smaller files, fewer quality control passes and fewer resources expended on mastering the multiple versions. For example, a censored version of a movie might differ in only a few video frames from the original. Instead of having to deliver or store two largely identical versions, IMF allows the censored version to reuse the Track Files of the original version.

IMF can re-use Track Files to minimize resource usage for versions of audio-viual works.
IMF Track File Reuse

Specifications

IMF is specified in the ST 2067 family of standards managed by SMPTE[3].

IMF is organized into three main categories:

  • core constraints[4], to which all IMF implementations conform and representing the bulk of the IMF standard;
  • applications, which target specific use cases; and
  • plug-ins, which contain optional technology that can be used across multiple applications.

The core constraints are specified in SMPTE ST 2067-2 (Core Constraints)[4]. An example of an application is Application #2E, which is specified in SMPTE ST 2067-21[7] and targets studio masters. One of the plugins is the Immersive Audio Bitstream Level 0 Plug-in, which is specified in SMPTE ST 2067-201[8] and adds support for immersive sound.

Example uses

IMF is specified by professional content creators for delivery of their content, including: BBC[9], Netflix[10] and Disney[11]

Supported essence

IMF supports a wide range of audio-visual essence and metadata, including:

  • Video up to 8192x6224 rasters, lossy and lossless compression, high-dynamic range, wide color gamut and stereoscopic 3D,[7]
  • 24-bit 48 kHz channel-based sound, arranged in arbitrary configurations
  • Immersive Audio Bitstream (IAB) immersive sound[12]
  • Subtitles and captions that conform to the TTML Profiles for Internet Media Subtitles and Captions 1.1 (IMSC 1.1) W3C Recommendation[13]

History

The need for IMF arose from various projects in the film and television industries[14] that identified component-based working as a more efficient mechanism for handling the very large volumes of very large files created when delivering cinema and television content around the globe[15]. With help from the Entertainment Technology Center[16], the SMPTE created the first version of the standard in 2013. The IMF User Group (IMF UG) was created by the Hollywood Professional Association shortly after and the IMF UG fosters active discussions between content owners, technologists, logistics specialists and software providers on best current practise for delivering large volumes of localised content in a resource efficient way. The IMF UG has created an IMF explainer in miultiple languages[1]

References

  1. ^ a b "EXPLAINER: Interoperable Master Format (IMF) – IMF UG". Retrieved 1 April 2022.
  2. ^ 2018-09-16T11:26:00+01:00. "IMF: A gateway to component-based workflows". IBC. Retrieved 20 May 2022.{{cite web}}: CS1 maint: numeric names: authors list (link)
  3. ^ a b "OV 2067-0-2021 - SMPTE Overview Document - Interoperable Master Format". OV 2067-0-2021: 1–4. August 2021. doi:10.5594/SMPTE.OV2067-0-2021.
  4. ^ a b c "ST 2067-2:2020 - SMPTE Standard - Interoperable Master Format — Core Constraints". ST 2067-2:2020: 1–43. May 2020. doi:10.5594/SMPTE.ST2067-2.2020.
  5. ^ "ST 2067-3:2020 - SMPTE Standard - Interoperable Master Format — Composition Playlist". ST 2067-3:2020: 1–35. May 2020. doi:10.5594/SMPTE.ST2067-3.2020.
  6. ^ "ST 2067-5:2020 - SMPTE Standard - Interoperable Master Format — Essence Component". ST 2067-5:2020: 1–15. May 2020. doi:10.5594/SMPTE.ST2067-5.2020.
  7. ^ a b "ST 2067-21:2020 - SMPTE Standard - Interoperable Master Format — Application #2E". ST 2067-21:2021: 1–34. May 2020. doi:10.5594/SMPTE.ST2067-21.2020.
  8. ^ "ST 2067-201:2021 - SMPTE Standard - Immersive Audio Bitstream Level 0 Plug-in". ST 2067-201:2021: 1–14. January 2021. doi:10.5594/SMPTE.ST2067-201.2021.
  9. ^ "TechnicalDeliveryStandardsBBCUHDiPlayerSupplement.pdf" (PDF). Dropbox. Retrieved 4 March 2022.
  10. ^ "Netflix Branded Delivery Specifications v4.1". Netflix | Partner Help Center. Retrieved 4 March 2022.
  11. ^ "Disney Media Tech Specs". mediatechspecs.disney.com. 27 April 2021. Retrieved 4 March 2022.
  12. ^ "ST 2098-2:2019 - SMPTE Standard - Immersive Audio Bitstream Specification". ST 2098-2:2019: 1–54. June 2019. doi:10.5594/SMPTE.ST2098-2.2019.
  13. ^ "TTML Profiles for Internet Media Subtitles and Captions 1.1". www.w3.org. Retrieved 4 March 2022.
  14. ^ "© 2011 AmberFin Limited Loose Coupling for Multipurpose Distribution Bruce Devlin Chief Technical Officer. - ppt download". slideplayer.com. Retrieved 1 April 2022.
  15. ^ Blog, Netflix Technology (19 April 2017). "The Netflix IMF Workflow". Medium. Retrieved 1 April 2022.
  16. ^ "ETC". www.etcenter.org. Retrieved 1 April 2022.
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