Statistics about Podcast Chapters

Some podcast publishers choose to provide additional chapter information when they publish their podcast episodes, breaking down a single episode into multiple segments - each of which may have a title, link, image, etc.

Right now, there are four mechanisms that podcasters can use to do this:

  1. Embed chapter information directly inside the MP3 audio file using standard ID3 tags, with tools such as Forecast.
  2. Embed chapter information directly inside the AAC/M4A audio file using MPEG-4 Chapter Lists.
  3. Include chapter information inside the RSS feed at the episode level using the Podlove Simple Chapters spec, first published in 2012.
  4. Create a separate json file with the chapter information, and reference it from the RSS feed at the episode level using the newer Podcast Namespace Chapters spec.

Apple published Using chapters on Apple Podcasts earlier this year to highlight this little-known feature of podcasting.

Since we already analyze every single new podcast episode published to produce our podcast host, tracker, and CDN rankings, we are in a good position to see how often podcast chapters are used in the wild, and which mechanisms are most prevalent.

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Podcast Chapters frequency, by mechanism

as a percentage of all new episodes published in the given month

Month Any Chapters ID3 Chapters Namespace Chapters Podlove Chapters M4A Chapters
January 2022 1.22% 0.87% 0.18% 0.05% 0.02%
February 2022 1.22% 0.85% 0.19% 0.05% 0.02%
September 2022 1.50% 1.29% 0.44% 0.06% 0.02%
April 2024 2.20% 1.93% 1.26% 0.39% 0.02%

Of the 1.8 million new episodes in April 2024, about 1 in every 45 provide chapter information.

ID3 tag-based chapters are the most popular mechanism:

Description-based chapters

Some apps also parse chapter-looking markup (timestamps and titles) out of episode descriptions. If this less-structured format is included, it raises the percentage of new episodes with chapter information:

Month Any Chapters Spotify Chapters 1
April 2024 3.73% 1.70%

This would make description-based chapters the second-most popular mechanism, just behind ID3 chapters - and mostly non-overlapping with other mechanisms.

With these included, about 1 in every 27 new podcast episodes provide chapter information of some kind.

Analysis by John Spurlock

Thanks to the Podcast Index for crawling every podcast, and giving us a signal of when to check for new episodes.

Updated 2024-05-19, with data for the month of April 2024.

Updated 2022-10-02, with data for the month of September 2022.

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  1. Using the format found to produce chapter UI blocks in Spotify ↩︎