IMF: One Format to Rule Them All or Just One More Format?
The Interoperable Master Format (IMF) holds the promise of drastically reducing the number of different versions of a file that a video publisher needs to deliver to viewers—a promise so strong that the world’s leading video subscription service has been taking notice.
“A few years ago we discovered the Interoperable Master Format (IMF), a standard created by the Society of Motion Picture and Television Engineers (SMPTE),” wrote Chris Fetner and Brian Kenworthy in a Netflix Tech Blog posting in late 2016. “By using this standard, Netflix is able to hold a single set of core assets and the unique elements needed to make those assets relevant in a local territory.”
“[Our global] supply chain needed an efficient way to vault our masters in the cloud that didn’t require a different version for every territory in which we have our service,” Fetner and Kenworthy wrote.
So what is IMF and where did it come from? And what are the benefits and limitations of IMF? This article highlights several of those key areas, including the use of an extensible markup language (XML) and the material exchange format (MXF), the audio- and video-track container format that underlies IMF.
“The goal behind IMF is to provide a single interchangeable master file format primarily for distribution,” says David Schleifer, Primestream’s chief operating officer.
Schleifer, who provided a good bit of detail for last month’s article “MAM and DAM Evolve Into the Cloud,” noted that Primestream strives to support the latest standards as a way to deliver new workflows and efficiencies their customers. However, he warned that IMF isn’t exactly a universal format when it comes to the acquisition and post-production processes.
“We do not currently see IMF as a format in the production process upstream from distribution,” says Schleifer, “but rather as a deliverable for the final product.”
Understanding IMF: Bits and Bobs
The IMF family of standards, according to SMPTE, is maintained by its Media Packaging and Interchange Committee 35PM. IMF is a superset of MXF and XML, with the benefits of both in addition to the ability to move beyond MXF’s binary-based versioning (to what IMF refers to as the Composite Playlist, or CPL).
A good overview of MXF and how it compares to IMF can be found in a blog post by Dalet’s Bruce Devlin. The blog post argues that XML, which has been used for everything from Microsoft Word to websites, is a more approachable option for creating playlists.
“There are maybe 20 or 30 really good MXF binary programmers in the world today,” writes Devlin. “XML is much more generic, and there must be hundreds of thousands of top quality XML programmers out there.”
In essence, IMF uses XML as a human-readable way to represent various content versions while, according to Devlin, “maintaining the proven AS02 media wrapping to store the essence components.”
The entire standard resides under SMPTE ST 2067, with the most recent versions being designated as 2016, such as the Core Constraints standard, which is ST 2067-2:2016.
In addition to the ST 2067-5 essence components—including audio, basic metadata, timed text, and video—the SMPTE family of IMF standards also maintains a series of profile lists (100-103, currently) as well as key application use cases.
The profile lists, which were last updated in 2014, provide common image or audio definitions and macros, as well as common image pixel color schemes.
The applications are where the heavy lifting—or at least the previous thoughtful constructing of typical use cases for the IMF container format—is done.
For instance, Application 2 is geared toward “studio applications where a TV or movie title is transformed into multiple content versions (airline edits, special edition, languages...) that are made available to multiple consumer distribution channels (internet, optical media, broadcast...) across multiple territories and over the span of many months to over a year.”
The Netflix Tech Blog post explains one of the practical approaches to the Application 2 use case. In their blog post, Fetner and Kenworthy point out that that for certain titles, such as the Netflix-owned Narcos series, the video asset is largely the same in all territories, although key elements at the beginning and end of an episode might change, such as the post-episode title sequence.
“[W]e can hold the Primary AV and the specific frames that are different for, say, the Japanese title sequence version,” Fetner and Kenworthy wrote. “This reduces duplication of assets that are 95 percent the same and allows us to hold that 95 percent once and piece it to the 5 percent differences needed for a specific use case.”
Playing Content in an IMF Container Format
While the main assets, or essence, of an IMF container center on audio and video, another powerful feature of the IMF family of standards is the ability to play back content.
ST 2067-3:2016 uses the underpinnings of XML to generate a CPL that acts as a “representation of a single version of a finished IMF composition (feature, episode, trailer, advertisement, etc.).”
The CPL contains the information necessary to describe the composition and to synchronize its underlying essence for a series of use cases, from playout or transcoding.
Because it uses XML, it is both extensible, in terms of how the playlist is laid out and new features are added, as well as readable by humans. As ST 2067-3:2016 currently stands, it is designed for file-based operations.
An example of a company seeing immediate benefit from IMF playback functionality is Prime Focus Technologies.
“PFT is a strong supporter of the Interoperable Master Format because it is aligned with two of our driving principles,” says Ramki Sankaranarayanan, CEO and founder of Prime Focus Technologies.
“The first of these is helping media enterprises better manage the business of content, and the second is using automation to boost efficiency and cost-effectiveness when syndicating across platforms, regions, and audiences,” Sankaranarayanan says.
Prime Focus has created an IMF-compatible player that provides the preview, review, and playback. In addition, the player can distribute, over a streaming proxy, a CPL with all its essences including video, audio, and timed text (e.g., captions, subtitles).
Storing Assets Within IMF
One area where IMF offers promise is the ability to move full packages of content around without requiring a relinking step that’s often necessary in many container formats.
As referenced in the Netflix Tech Blog, above, lowering overall storage requirements is a sizable benefit of avoiding duplication of assets.
But there’s also another benefit, wherein IMF acts almost like a folder on a desktop computer, holding multiple assets in a single logical storage location.
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