# OpenSpec Change: enterprise-audio-sprite-packer

- **Change ID**: enterprise-audio-sprite-packer
- **Package**: `@suaveplan/audio-sprite-packer`
- **Category**: universal
- **Target path**: `universal/compression/audio-sprite-packer`
- **Status**: PROPOSED
- **Date**: 2026-04-24
- **Reference spec**: `/mnt/s/web/suaveplan/enterprise/audio-sprite-packer.md`

---

## Summary

Deliver `@suaveplan/audio-sprite-packer` on the genesis branch from scratch at enterprise quality. The package builds binary audio sprite maps with 80%+ compression versus individual files: pack multiple audio clips (WAV/MP3/OGG) into a single concatenated binary with a compact JSON manifest (offset + duration per clip), strip inter-clip silence, normalise gain, and produce a ready-to-use sprite descriptor compatible with Web Audio API `AudioBufferSourceNode`. Pure TypeScript; audio encode/decode delegated to injectable `AudioAdapter`.

---

## Current-state audit (genesis)

The package does not exist on genesis yet — this is a fresh build. No prior source, no test results, no coverage data.

---

## Available workspace deps on genesis

| Package | Role |
|---|---|
| `@suaveplan/error` (`workspace:^`) | Base class for `AudioSpriteError`; `AUDIO_SPRITE.*` codes |
| `@suaveplan/types` (`workspace:^`) | `LoggerLike`, `Clock` |
| `@suaveplan/mime` (`workspace:^`) | Audio MIME-type detection |
| `@suaveplan/crypto-utils` (`workspace:^`) | Content hash for deterministic manifest IDs |
| `zod` (`catalog:forms`) | Zod schemas for all public option types |
| `@opentelemetry/api` (`catalog:observability`) | Spans + counters |

Dev deps: `vitest`, `@vitest/coverage-istanbul`, `fast-check`, `mitata` (all `catalog:testing`).

---

## Public API

### Core types

```ts
class AudioSpriteError extends SuaveplanError

type AudioFormat = 'wav' | 'mp3' | 'ogg' | 'flac' | 'unknown'

interface AudioClipInput {
  name: string
  data: Uint8Array
  format?: AudioFormat       // detected from @suaveplan/mime if absent
}

interface AudioSpriteEntry {
  name: string
  offset: number             // byte offset in the packed buffer
  byteLength: number
  durationSeconds: number
  sampleRate: number
  channels: number
  format: AudioFormat
}

interface AudioSpriteManifest {
  version: 1
  format: AudioFormat
  sampleRate: number
  channels: number
  totalDurationSeconds: number
  entries: AudioSpriteEntry[]
  contentHash: string         // SHA-256 of packed buffer
}

interface AudioSprite {
  data: Uint8Array            // concatenated packed audio bytes
  manifest: AudioSpriteManifest
}

interface PackOptions {
  outputFormat?: AudioFormat   // default: 'ogg'
  silencePaddingMs?: number    // between clips; default: 100
  stripSilence?: boolean       // default: true; remove leading/trailing silence per clip
  normalise?: boolean          // default: false; gain normalisation
  sampleRate?: number          // default: from first clip
}

interface AudioAdapter {
  readonly supportedFormats: readonly AudioFormat[]
  probe(data: Uint8Array): Promise<{ durationSeconds: number; sampleRate: number; channels: number; format: AudioFormat }>
  decode(data: Uint8Array): Promise<Float32Array>                       // PCM samples
  encode(samples: Float32Array, sampleRate: number, channels: number, format: AudioFormat): Promise<Uint8Array>
  stripSilence(samples: Float32Array, sampleRate: number, thresholdDb?: number): Float32Array
  normalise(samples: Float32Array): Float32Array
}

interface AudioSpritePackerOptions {
  adapter: AudioAdapter
  logger?: LoggerLike
  clock?: Clock
}

class AudioSpritePacker {
  constructor(options: AudioSpritePackerOptions)
  pack(clips: AudioClipInput[], options?: PackOptions, signal?: AbortSignal): Promise<AudioSprite>
  unpack(sprite: AudioSprite, clipName: string): Uint8Array
}

function createAudioSpritePacker(options: AudioSpritePackerOptions): AudioSpritePacker
```

### Error codes

```ts
type AudioSpriteErrorCode =
  | 'AUDIO_SPRITE_UNSUPPORTED_FORMAT'
  | 'AUDIO_SPRITE_DECODE_FAILED'
  | 'AUDIO_SPRITE_ENCODE_FAILED'
  | 'AUDIO_SPRITE_CLIP_NOT_FOUND'
  | 'AUDIO_SPRITE_INVALID_OPTIONS'
  | 'AUDIO_SPRITE_EMPTY_INPUT'

const AUDIO_SPRITE_ERROR_METADATA: Readonly<Record<AudioSpriteErrorCode, CodeMetadata>>
function registerAudioSpriteErrorCodes(): void
```

### Zod schemas

```ts
AudioSpriteEntrySchema
AudioSpriteManifestSchema
PackOptionsSchema
AudioSpritePackerOptionsSchema
```

---

## New additions for genesis

1. **`AudioAdapter` interface** — all PCM operations delegated; `NullAudioAdapter` ships for tests.
2. **Silence stripping** — optional per-clip silence removal using a configurable dB threshold (default: −60 dBFS).
3. **Gain normalisation** — peak normalise each clip to 0 dBFS before packing (optional).
4. **Content hashing** — SHA-256 of packed buffer via `@suaveplan/crypto-utils` stored in manifest for integrity verification on unpack.
5. **`unpack`** — slice-and-return: uses `manifest.entries` to extract a named clip from the sprite buffer without any re-decode.
6. **`AbortSignal` propagation** — passed through `pack`; throws `AudioSpriteError(AUDIO_SPRITE_ENCODE_FAILED)` on abort.
7. **OTel instrumentation** — span `audio-sprite.pack`, counter `audio_sprite_pack_total`, histogram `audio_sprite_pack_duration_ms` + `audio_sprite_compression_ratio`.
8. **Property-based tests** — unpack after pack returns original bytes (null adapter), manifest entry count matches input clip count, silence padding produces correct total duration.
9. **Benchmark suite** — pack 10 short clips (null adapter), pack 50 clips.

---

## File layout

```text
universal/compression/audio-sprite-packer/
  package.json
  tsconfig.json
  vitest.config.ts
  src/
    index.ts
    error-codes.ts
    constants/
      index.ts
    types/
      common.ts
      common.md
    core/
      audio-sprite-packer/
        audio-sprite-packer.ts
        audio-sprite-packer.md
        audio-sprite-packer.types.ts
        audio-sprite-packer.test.ts
        index.ts
    adapters/
      null-adapter/
        null-adapter.ts
        null-adapter.md
        null-adapter.test.ts
        index.ts
    utils/
      manifest.ts
      manifest.md
      manifest.test.ts
    __benchmarks__/
      audio-sprite-packer.bench.ts
  tests/
    integration.test.ts
    property.test.ts
```

---

## Impact

**Downstream**: game audio engines, `@suaveplan/audio-engine`, any Web Audio sprite loaders.
**Breaking changes**: none — fresh build.
**Prerequisites**: `@suaveplan/error`, `@suaveplan/types`, `@suaveplan/mime`, `@suaveplan/crypto-utils` published to Verdaccio.