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Screenshot of the "Documenting Accessibility Features" webpage that describes the work that the Formats team did to document Accessibility Feature information in FDDs.
New entry on the Sustainability of Digital Formats about documenting accessibility support in file formats. Read more below.

More Formats and More About Formats: New Entries, Format Accessibility Features and Other Updates

Posted by: Liz Holdzkom

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Today’s guest post is from Kate Murray, Marcus Nappier, Liz Holdzkom and Genevieve Havemeyer-King of the Digital Collections Management & Services Division at the Library of Congress.

It’s hard to believe that this is our sixth installment of file format fandom blog posts! The traditional sixth anniversary gift is something made from iron but that seems like a pain to giftwrap. So just send us good vibes, comments and questions instead.

Way back in 2021 with our inaugural post, Fun with File Formats, we had only eight content categories with approximately 480 FDDs or format description documents. Three years later, we have 12 content categories and 568 FDDs. Any way you slice it, we have been busy. If you are imagining that meme with the cat frantically typing on a laptop, that is an accurate representation of your favorite Formats team at work.

New Format Descriptions Galore

Without a doubt, the main contributor to our impressive FDD output this year was the now-concluded contract with Myriad Consulting (Ashley Blewer, Frances Harrell and Abi Simkovic). Their good work contributed 32 new entries to the Sustainability of Digital Formats, alongside seven new entries authored by Library of Congress staff.

Screenshot showing spreadsheet that lists the FDDs that have been published in 2024, with FDD details like short and long name for the format and publication date
Screenshot of the publication log of all the FDDs published so far in 2024.

As Marcus explained in How to Write a FDD in 149 Easy Steps: Learning to Evaluate Digital File Formats, researching and writing an FDD is a collaborative and labor-intensive task so there are lots of fingers in all these FDD pies. It is the ultimate group project.

Since our last blog entry in December 2023, we posted the following new FDDS in specific areas of focus:

You can follow along at home with our progress on our workplan page as well as the regularly updated publication log. We’ve also published the draft workplan for the coming year if you want a sneak peak. This one is still very much in flux because we have no external contract support so it’s just us LC chickens on the FDD writing and updating duty again.

If you are curious about how and why we research the formats we do, read a refresher on our first post, Fun with File Formats. There’s a method to the madness but the gist is that we focus on formats that are of interest to the Library of Congress because we have them in our collections, such as those listed in the Recommended Formats Statement (more on the RFS below), or we will be adding them to our collections. Another path is that we encounter a format in the wild and want to learn about it in preparation for seeing it in our collections.

Documenting Digital Accessibility Features

Alongside these new format entries, we’ve also started a project related to the yearly update of the Recommended Formats Statement (RFS) to document digital accessibility features in order to help RFS Content Teams determine if a format is preferred or acceptable under the RFS guidance.

The key questions we sought to answer about digital accessibility include:

  • Does this format support digital accessibility features such as those described in the W3C Accessibility Principles? For example:
  • In what way are accessibility features implemented in the format? Such as:
    • Are there specific metadata tags to indicate accessibility features such as alt text, captions, transcripts and the like?
    • Are embedded closed captions supported?
    • Does the file rely on external data, such as a WebVTT file for caption data?

See the entry for WAVE Audio File Format (FDD001 – the very first FDD ever written!) which states:

Accessibility Features

WAVE files have moderate support for accessibility features. Closed captions and transcriptions can be embedded within the Labeled Text chunk (ltxt) [within the Associated Data Chunk] and identified as such with the ‘Purpose’ label. The specification includes the suggested Purpose value of ‘capt’ for closed-caption text and FADGI defines, in Guidelines for Embedding Metadata in Broadcast WAVE Files, the Purpose value of ‘tran’ for transcription. Overall, the optional Associated Data Chunk field allows a mechanism to provide context for the audio data along the timeline which is helpful, but it is not expressly designed for accessibility impacts.

In common practice, typically WAVE and other audio file content is supported by external caption and subtitle formats such as WebVTT. See W3C’s Making Audio and Video Media Accessible for more general information about accessible sound and moving image media.

This information is reported as part of Self Documentation, one of the seven sustainability factors. Each entry is prefaced with the Accessibility Features header in bold to make it easier to identify the information consistently on the page. It’s important to note that the RFS does not require these accessibility features to be enabled for a format, but our additions provide information on the capacity for the format to support these features.

We’ve defined the following levels of accessibility support for a format:

  • Unknown or not applicable: This term is used if there is no support identified in the specifications/resources or if unknown.
  • Limited: This term is used if there might be some very basic capability.
  • Moderate: This term is used if there is some support but perhaps not explicitly designed for accessibility or not actually used.
  • Good: This term is used if there are dedicated components in the file that support accessibility features, such as embedded metadata to label content, tagged text for reading order and structure for screen readers (such as in text files) or caption/subtitle/timecode/transcription options in AV wrappers.

The RFS Content Teams use the FDDs in their deliberations about preferences for the format as either “preferred” or “acceptable.” There are over 70 preferred formats listed in the RFS across all content categories, so we are tackling those first and we’ll get to the acceptable formats later. We also have plans to get wider community input on what information we’ve documented. While there’s a ways to go to organize and prettify this data as a compiled draft set, we’ve compiled it into a XLSX file in the interim so we can start to share and get feedback as we continue to refine our processes. Let us know what would be helpful to the community for this effort.

What’s Up Next

Your favorite Formats fam have lots in store for the next six months. We have a paper at iPres 2024 with colleagues from the US National Archives and Records Administration (NARA) about File Format Risk Assessment in Two U.S. Government Contexts, lots more FDDs to write, we’re thinking of updating our XML schema to accommodate some recent changes in how and what data we document (reminder that you can download all or part of our FDDs in XML!), and of course, continuing to refine our digital accessibility features work.

And of course, we love to hear from our users. All 170,272 unique visitors across six continents (come on Antarctica folks – complete the map and make some format nerds very happy!) since our last post in December 2023. As we say in many of our FDDs, comments welcome! Please drop us a note here or to [email protected].

Comments (5)

  1. Carl Fleischhauer says:

    Great to see the continued evolution of this resource, evidence of its continuing value to the community. I’ll hope that funds in the next budget cycle will support engaging some consultants-in-poultry (pun intended) to join the LC format-chickens in updating and expanding the offering.

  2. Micky Lindlar says:

    No questions from me, but sending plenty of good vibes and the comment “THANK YOU” for setting up, maintaining and continuously extending this resource used by digital preservationists and file format fans around the world.

  3. Marcos Sueiro Bal says:

    Thank you for your great work on this important set of documents!

  4. Danylù Calabrese says:

    What an impressive update! Seeing the Sustainability of Digital Formats portfolio grow to 568 FDDs across 12 content categories is remarkable, and the behind-the-scenes collaboration you describe is truly evident in the depth of each new entry. I’m particularly excited about the systematic documentation of digital accessibility features. By mapping W3C principles to concrete fields in every FDD, you’re providing RFS content teams (and the broader preservation community) with a practical way to weigh accessibility alongside more traditional sustainability factors.
    Two quick questions:
    Have you considered exposing the new “Accessibility Features” data via an API or bulk-download JSON as you already do for the XML workset? That would make it easier for memory institutions to integrate the levels (Unknown → Good) into automated risk-assessment workflows.
    Once the preferred-format analysis is complete, might you publish a short methodology note on how you calibrated those levels? A transparent rubric would help external contributors apply the same criteria when proposing updates.
    Thanks again to the whole Formats team for the meticulous research and for inviting community feedback at each step. This work is invaluable for anyone making long-term preservation decisions.

    • Liz Holdzkom says:

      Thank you for these kind words and support for the Sustainability of Digital Formats work. You might want to read our more recent blog post, New File Format Research and Documentation on the Sustainability of Digital Formats (June 12, 2025) where we detail our additional work related to documenting accessibility support in selected file formats listed in the Recommended Formats Statement. We are slowly making our way through the remaining entries, but this is a long-term project.

      We are always looking to improve our resources to best meet the needs of our users and have discussed a JSON option. It’s still a way down the path though. Meanwhile, the structured XML is available for ingest.

      Thank you for the prompt for more clarity about the determination process. We might augment our Documenting Accessibility Features page with some more information. We have some internal guidelines about what we are looking for in the content categories. For example, “Accessibility features for 3D model formats include audio descriptions for screen readers to enable user interactivity events such as object selection, rotation and zoom, alt text for image forms, color contrast definition as well as caption and subtitle support.”

      And we are now up to 590 entries and counting! Check out our workplan to see what’s coming next.

      –The Formats Team

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