# EGG-03: Audio plane (moq-lite)

`status: draft`
`requires: EGG-02`
`category: required`

## Summary

Audio is carried over [moq-lite](https://github.com/kixelated/moq) Lite-03 on
top of the WebTransport session opened in EGG-02. Each speaker publishes one
broadcast keyed by their pubkey hex, on a single track named `audio/data`,
encoded as Opus.

This EGG defines the broadcast/track naming convention and the audio codec
parameters. It does not redefine moq-lite framing — refer to the upstream
spec for the wire layout of `Subscribe`, `Announce`, `Group`, and `Frame`
control messages.

## Wire format

### Speaker → relay (publish)

A speaker MUST send a moq-lite `Announce` with:

```
prefix     = ""           (empty — relative to the JWT's `root` namespace)
suffix     = <pubkey hex>
status     = Active
```

After the announce, the speaker opens a unidirectional QUIC stream per group,
prefixed with a moq-lite `Group` header followed by `Frame`s carrying Opus
payloads.

### Listener → relay (subscribe)

A listener MUST send a moq-lite `Subscribe` with:

```
broadcast  = <speaker pubkey hex>
track      = "audio/data"
priority   = 128            (recommended)
ordered    = true
maxLatency = 0              (unlimited)
```

The relay forwards each subsequent `Group` and its `Frame`s to the listener
in subscribe-id order.

### Codec

| Parameter       | Value                                 |
|-----------------|---------------------------------------|
| Codec           | Opus (RFC 6716)                       |
| Sample rate     | 48 kHz                                |
| Channels        | 1 (mono)                              |
| Frame duration  | 20 ms (960 samples)                   |
| Bit-rate target | 32 kbit/s (configurable, no upper cap)|
| VBR             | Allowed                               |

A new `Group` MUST be opened on every Opus reset (e.g. mute/unmute).

## Behavior

1. A speaker MUST emit an `Announce` with `status=Active` immediately after
   the WebTransport session reaches a usable state, and emit `status=Ended`
   when stopping the broadcast cleanly.
2. A speaker MUST cap their broadcast to one concurrent `audio/data` track
   per session. Multi-quality stacks are reserved for a future EGG.
3. Listeners MUST tolerate gaps in the group sequence (frames dropped due to
   network loss). They MUST NOT request retransmits.
4. Listeners SHOULD subscribe with `ordered=true`. Out-of-order delivery
   would re-introduce reorderable jitter the Opus decoder is not equipped to
   handle.
5. A speaker MUST encode in mono. Stereo broadcasts are reserved for a future
   EGG.
6. Listeners MUST NOT subscribe to their own broadcast (would create an audio
   loopback through the relay).
7. The relay MUST drop a publishing peer's `Announce` and any subsequent
   stream data if the JWT's `put` claim does not contain `<pubkey hex>`.

## Example

A two-speaker room:

```
A's session:  ANNOUNCE  prefix="" suffix="speakerA" status=Active
              GROUP     subscribe-id=…, sequence=0
              FRAME     <opus payload, 20ms>
              FRAME     <opus payload, 20ms>
              …

Listener's session:
  SUBSCRIBE  broadcast="speakerA" track="audio/data"
  ←  GROUP   sequence=0
  ←  FRAME   <opus payload, 20ms>
  ←  …
  SUBSCRIBE  broadcast="speakerB" track="audio/data"
  ←  GROUP   sequence=0
  ←  FRAME   <opus payload, 20ms>
  ←  …
```

## Compatibility

EGG-12 adds an OPTIONAL `catalog.json` track per broadcast carrying codec
metadata. EGG-12 MUST NOT change the `audio/data` track parameters defined
here.

A future "video plane" EGG MAY introduce additional tracks; their names MUST
NOT collide with `audio/data` or `catalog.json`.