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The Podcast ActivityStream

Version 1.0 by Yassine Doghri - 2021.04.15

The document aims to explain through examples and namespace definition how the existing RSS specification could be interfaced to ActivityPub.

This is meant as a complementary work to the existing RSS podcast namespace specification whilst unlocking features offered by the ActivityPub protocol.

Context

A Podcast show is essentially constituted of two entities. In the RSS specification, these are placed under the <channel> and <item> tags. The <channel>, referring to the Podcast, may include multiple <item> tags which are the Podcast episodes.

The ActivityPub protocol is a decentralized social networking protocol based upon the ActivityStreams 2.0 data format. This offers a base vocabulary for social interactions between decentralized servers and allows us to extend it for podcasting.

The syntax for defining the ActivityStreams 2.0 data format is called JSON-LD, a method of encoding linked data using JSON.

Just as the RSS specification, the Podcast ActivityStream defines two entities:

The Podcast Actor

The Podcast Actor extends the Actor Object from ActivityPub to include specific podcast attributes.

Here is an example of a Podcast Actor:

{
  "@context": [
    "https://www.w3.org/ns/activitystreams",
    "https://w3id.org/security/v1",
    "https://github.com/Podcastindex-org/activitypub-spec-work/blob/main/docs/1.0.md"
  ],
  "to": ["https://www.w3.org/ns/activitystreams#Public"],
  "id": "https://podcast.demo/podcasts/DemoPodcast",
  "type": "Podcast",
  "rss": "https://podcast.demo/podcasts/DemoPodcast/feed.xml",
  "name": "The Demo Podcast",
  "preferredUsername": "DemoPodcast",
  "summary": "<p>This is a demonstration of the activitypub protocol applied to Podcasts!</p>",
  "inbox": "https://podcast.demo/podcasts/DemoPodcast/inbox",
  "outbox": "https://podcast.demo/podcasts/DemoPodcast/outbox",
  "followers": "https://podcast.demo/podcasts/DemoPodcast/followers",
  "following": "https://podcast.demo/podcasts/DemoPodcast/following",
  "episodes": "https://podcast.demo/podcasts/DemoPodcast/episodes",
  "url": "https://podcast.demo/podcasts/DemoPodcast",
  "image": {
    "type": "Image",
    "mediaType": "image/jpeg",
    "url": "https://podcast.demo/media/podcasts/DemoPodcast/cover.jpg"
  },
  "icon": {
    "type": "Image",
    "mediaType": "image/jpeg",
    "url": "https://podcast.demo/media/podcasts/DemoPodcast/avatar.jpg"
  },
  "language": "en",
  "category": "Fiction > Science Fiction",
  "explicit": false,
  "publisher": {
    "@type": "Organization",
    "name": "John Doe Corp.",
    "email": "contact@johndoe.demo"
  },
  "author": {
    "@type": "Person",
    "name": "Jane Doe",
    "email": "jane.doe@podcast.demo"
  },
  "owner": {
    "@type": "Person",
    "name": "John Doe",
    "email": "john.doe@podcast.demo"
  },
  "persons": "https://podcast.demo/podcasts/DemoPodcast/persons",
  "location": {
    "@type": "Place",
    "geo": {
      "@type": "GeoCoordinates",
      "latitude": "48.8566969",
      "longitude": "2.3514616"
    },
    "name": "Paris, France"
  },
  "trailer": "https://podcast.demo/podcasts/DemoPodcast/trailer",
  "copyrightHolder": {
    "@type": "Person",
    "name": "Jane Doe",
    "sameAs": "https://en.wikipedia.org/wiki/jane_doe"
  },
  "copyrightNotice": "(CC BY-ND 4.0)",
  "copyrightYear": 2021,
  "discoverable": false,
  "complete": false,
  "locked": true,
  "license": "https://creativecommons.org/licenses/by-nd/4.0/",
  "value": {
    "type": "Value",
    "id": "https://podcast.demo/podcasts/DemoPodcast/value",
    "method": "keysend",
    "suggested": "0.00000005000",
    "valueRecipients": "https://podcast.demo/podcasts/DemoPodcast/value/recipients"
  },
  "publicKey": {
    "id": "https://podcast.demo/podcasts/DemoPodcast#main-key",
    "owner": "https://podcast.demo/podcasts/DemoPodcast",
    "publicKeyPem": "-----BEGIN PUBLIC KEY----- ... -----END PUBLIC KEY-----"
  }
}

Notes about the attributes

  • publisher corresponds to the author tag in the itunes RSS spec.
  • discoverable defines whether or not the podcast (or episode) should be visible on other platforms. Corresponds to the block tag in the itunes RSS spec.
  • complete whether or not the podcast show is over (no more new episodes to be expected).
  • movedTo corresponds to the new-feed-url tag in the rss feed. Adopted by Mastodon though not an officially.

The PodcastEpisode Object

The PodcastEpisode Object extends the base Object type from ActivityPub to include all attributes specific to a podcast episode. It also includes an extended Audio Object for the podcast episode's audio file.

Here is an example of a PodcastEpisode Object:

{
  "@context": [
    "https://www.w3.org/ns/activitystreams",
    "https://github.com/Podcastindex-org/activitypub-spec-work/blob/main/docs/1.0.md"
  ],
  "type": "PodcastEpisode",
  "id": "https://podcast.demo/podcasts/DemoPodcast/episodes/example-episode",
  "attributedTo": "https://podcast.demo/podcasts/DemoPodcast",
  "to": ["https://www.w3.org/ns/activitystreams#Public"],
  "cc": ["https://podcast.demo/podcasts/DemoPodcast/followers"],
  "name": "An Example PodcastEpisode Object",
  "description": {
    "type": "Note",
    "mediaType": "text/markdown",
    "content": "Here is the description for the **demo episode**!",
    "contentMap": {
      "en": "<p>Here is the description for the <strong>demo episode</strong>!</p>",
      "fr": "<p>Voici la description pour la <strong>démo de l’épisode</strong> !</p>"
    }
  },
  "image": {
    "type": "Image",
    "mediaType": "image/jpeg",
    "url": "https://podcast.demo/media/example-episode_cover.jpg"
  },
  "audio": {
    "id": "https://podcast.demo/podcasts/activitypub/episodes/example-episode.mp3",
    "type": "Audio",
    "name": "An Example PodcastEpisode Object",
    "size": 1962804,
    "bitrate": 320000,
    "duration": 42,
    "url": {
      "href": "https://podcast.demo/media/example-episode.mp3",
      "type": "Link",
      "mediaType": "audio/mpeg"
    },
    "caption": "https://podcast.demo/media/example-episode/caption",
    "transcript": "https://podcast.demo/media/example-episode/transcript",
    "chapters": "https://podcast.demo/media/example-episode/chapters"
  },
  "partOfSeason": "https://podcast.demo/podcasts/DemoPodcast/seasons/1",
  "episodeNumber": 1,
  "explicit": false,
  "location": {
    "@type": "Place",
    "geo": {
      "@type": "GeoCoordinates",
      "latitude": "48.8566969",
      "longitude": "2.3514616"
    },
    "name": "Paris, France"
  },
  "discoverable": true,
  "replies": "https://podcast.demo/podcasts/DemoPodcast/episodes/example-episode/replies",
  "published": "2021-04-15T18:00:00Z"
}

The JSON-LD namespace definition

The ActivityStreams base vocabulary was extended to create The Podcast JSON-LD namespace

Going further

The JSON-LD syntax offers a wide range of features that go beyond the RSS file: direct social interaction, pagination, translations, etc.

You can check out the examples folder to get a glimpse into the possibilities of ActivityPub.

This work has been inspired and made possible with the amazing free and open-source projects on the internet: