Voice Messages

1 Overview

Some things are easier to say than to type. This NIP defines a voice message: a short audio clip, typically up to 60 seconds long, published as a Nostr event. It gives voice posts their own kinds, so audio feeds do not mix with kind-1 text notes.

The NIP defines two event kinds. Kind 1222 is a root voice message. It starts a thread. Kind 1244 is a voice reply. It answers a root message or another reply, and follows the comment structure of NIP-22.

The audio itself does not live inside the event. The event content is a URL that points directly to an audio file on a media server. Clients download or stream the file from that URL. An optional imeta tag from NIP-92 carries a waveform and a duration, so clients can draw a preview before they fetch any audio.

2 Root Voice Messages: Kind 1222

A kind 1222 event is a standalone voice post. It is a regular event under the NIP-01 storage rules. Its fields follow these rules:

The audio file itself has two SHOULD rules:

• Format. The file SHOULD be audio/mp4 (.m4a) with AAC or Opus encoding. Clients MAY support other common formats such as audio/ogg, audio/webm, or audio/mpeg (mp3). The spec recommends audio/mp4 for broad compatibility and efficiency.
• Duration. The audio SHOULD be no longer than 60 seconds. A publishing client SHOULD enforce this limit, or show the user a clear warning when the recording exceeds it.

3 Voice Replies: Kind 1244

A kind 1244 event is a voice reply. Its content and audio rules are identical to kind 1222:

• content MUST be a URL that points directly to an audio file.
• The file SHOULD be audio/mp4 (.m4a) with AAC or Opus encoding; clients MAY support audio/ogg, audio/webm, or audio/mpeg.
• The audio SHOULD be no longer than 60 seconds; enforce the limit or warn the user.
• Tags from other NIPs MAY be included, such as t and g.

One rule is extra: a kind 1244 event MUST follow the threading structure of NIP-22. Uppercase tags (E, K, P) point to the root voice message. Lowercase tags (e, k, p) point to the direct parent. In a top-level reply, root and parent are the same event.

4 Visual Preview with imeta

Downloading audio just to draw a feed is wasteful. The event MAY carry an imeta tag from NIP-92, so clients can render a visual preview without fetching the audio file first. Two imeta entries matter here:

5 Worked Example

A real root voice message, taken from the spec. The content URL points to an 8-second clip on a media server. The imeta tag repeats the URL and adds the waveform and duration:

{
  "content": "https://blossom.primal.net/5fe7df0e46ee6b14b5a8b8b929
              39e84e3ca5e3950eb630299742325d5ed9891b.mp4",
  "created_at": 1752501052,
  "id": "...",
  "kind": 1222,
  "pubkey": "...",
  "sig": "...",
  "tags": [
    [
      "imeta",
      "url https://blossom.primal.net/5fe7df0e46ee6b14b5a8b8b929
       39e84e3ca5e3950eb630299742325d5ed9891b.mp4",
      "waveform 0 7 35 8 100 100 49 8 4 16 8 10 7 2 20 10 100 100
       100 100 100 100 15 100 100 100 25 60 5 4 3 1 0 100 100 15
       100 29 88 0 33 11 39 100 100 19 4 100 42 35 5 0 1 5 0 0 11
       38 100 94 17 11 44 58 5 100 100 100 55 14 72 100 100 57 6
       1 14 2 16 100 100 40 16 100 100 6 32 14 13 41 36 16 14 6 3
       0 1 2 1 6 0",
      "duration 8"
    ]
  ]
}

A voice reply answers that message with a kind 1244 event. The tags follow NIP-22. Here the reply targets the root directly, so the uppercase and lowercase tags point to the same event:

-- Client B replies to root event a0f1c2... by pubkey 22a12a12... --
→ ["EVENT", {"kind":1244,
     "content":"https://media.example.com/reply-clip.m4a",
     "tags":[
       ["E", "a0f1c2...", "wss://relay.example.com", "22a12a12..."],
       ["K", "1222"],
       ["P", "22a12a12..."],
       ["e", "a0f1c2...", "wss://relay.example.com", "22a12a12..."],
       ["k", "1222"],
       ["p", "22a12a12..."],
       ["imeta", "url https://media.example.com/reply-clip.m4a",
        "waveform 0 12 40 88 60 22 5", "duration 6"]
     ],
     "created_at":1752501300, "id":"b7d3e4...", "pubkey":"f7234bd4...",
     "sig":"..."}]
← ["OK", "b7d3e4...", true, ""]

6 Version History

NIP-A0 is young and small. Its whole history is two commits, days apart:

• 20252025-07-27Updated the audio format and waveform recommendations: audio/mp4 with AAC or Opus became the recommended format (#1990).
• Origin2025-07-23Fabian published the initial spec: kinds 1222 and 1244, the 60-second guideline, and the imeta preview entries (#1984).

7 See Also

• NIP-01 — the base event format and client-relay flow that kinds 1222 and 1244 ride on.
• NIP-22 — the comment structure that kind 1244 replies must follow.
• NIP-92 — the imeta tag that carries the waveform and duration preview.
• NIP-94 — file metadata events for describing hosted media in more detail.
• NIP-71 — video events; the long-form cousin of voice messages.