# AudioMusicHandle

> Talos next · Since 0.6

The score.

Layers change on a bar line, never mid-phrase.

## Signature

```ts
export interface AudioMusicHandle {
  /**
   * Queue a layer from `meta.audio.music.layers`. The cross-fade begins at the next bar,
   * so the change lands on the beat. Returns the voice handle it will sound on, usable
   * with {@link AudioHandle.stop}, or 0 when the scene has no such layer.
   */
  play(layer: string, opts?: MusicOptions): number
}
```

Import: `import type { AudioMusicHandle } from "@argus/api"`

## Members

| Member | Signature | Description |
|---|---|---|
| `play` | `play(layer: string, opts?: MusicOptions): number` | Queue a layer from `meta.audio.music.layers`. The cross-fade begins at the next bar, so the change lands on the beat. Returns the voice handle it will sound on, usable with {@link AudioHandle.stop}, or 0 when the scene has no such layer. |

## Example

The tested fixture `fixtures/recipes/jump-pad-and-elevator/scenes/behaviors/camera-zone.ts`.

```ts
import type { Behavior } from "@argus/api"

/**
 * A trigger volume that retunes the camera while the player is inside it.
 *
 * The engine has no camera-zone concept and needs none: a volume, a `trigger` component and this.
 * Here the player's behaviour owns the camera (it re-sends its params when the view is turned), so
 * the zone tells it what to change rather than calling `ctx.camera.set` itself. In a scene where
 * nothing else writes the camera, the zone can call `ctx.camera.set(kind, params)` directly.
 */
interface Props {
  /** `ctx.camera.set` params to merge in on the way in, and on the way out. */
  inside?: Record<string, unknown>
  outside?: Record<string, unknown>
}

export default {
  onTrigger(ctx, trigger) {
    const params = trigger.entering ? ctx.props.inside : ctx.props.outside
    if (params) ctx.events.emit("camera-zone", { target: trigger.other.id, params })
  },
} satisfies Behavior<Record<string, never>, Props>
```