Simplify media stream implementation

README.md

@@ -93,8 +93,8 @@ Beyond the spec, for Node.js. Not portable to browsers.
 
 - **`addModule(fn)`** — register a processor via callback instead of URL, no file needed
 - **`sinkId: stream`** — pipe PCM to any writable: `new AudioContext({ sinkId: process.stdout })` then `node synth.js | aplay -f cd`
-- **`numberOfChannels`, `bitDepth`** — control output format in the constructor
-- **`navigator.mediaDevices.getUserMedia({ audio: true })`** — browser-parity microphone capture in Node. Load `web-audio-api/polyfill` and install [`audio-mic`](https://github.com/audiojs/audio-mic); browser mic code then runs verbatim. See the [mic FAQ](#how-do-i-capture-audio-from-the-microphone).
+- **`numberOfChannels`, `bitDepth`** — control output format in the constructor.
+- **`CustomMediaStreamTrack`** — extends `MediaStreamTrack` with a public constructor and `pushData(chunk, options)` to feed audio data (e.g. from a microphone). Prior art: `CanvasCaptureMediaStreamTrack`. See the [mic FAQ](#how-do-i-capture-audio-from-the-microphone).
 
 ## FAQ
 
@@ -147,35 +147,40 @@ const buffer = await ctx.decodeAudioData(readFileSync('track.mp3'))
 WAV, MP3, FLAC, OGG, AAC via [audio-decode](https://github.com/audiojs/audio-decode).
 </dd>
 
-<dt>How do I capture audio from the microphone?</dt>
+<dt id="how-do-i-capture-audio-from-the-microphone">How do I capture audio from the microphone?</dt>
 <dd>
 
-In Node, pair [`audio-mic`](https://github.com/audiojs/audio-mic) with `MediaStreamAudioSourceNode.pushData()`:
+In Node, pair [`audio-mic`](https://github.com/audiojs/audio-mic) with `CustomMediaStreamTrack`:
 
 ```sh
 npm install audio-mic
 ```
 
 ```js
-import { AudioContext, MediaStreamAudioSourceNode } from 'web-audio-api'
+import { AudioContext, MediaStreamAudioSourceNode, CustomMediaStreamTrack, MediaStream } from 'web-audio-api'
 import mic from 'audio-mic'
 
 const ctx = new AudioContext()
 await ctx.resume()
 
-const src = new MediaStreamAudioSourceNode(ctx, { numberOfChannels: 1, bitDepth: 16 })
+const track = new CustomMediaStreamTrack({
+  kind: 'audio',
+  label: 'mic',
+  settings: { channelCount: 1, sampleSize: 16, sampleRate: ctx.sampleRate }
+})
+const stream = new MediaStream([track])
+
+const src = new MediaStreamAudioSourceNode(ctx, { mediaStream: stream })
 src.connect(ctx.destination) // live monitor
 
 const read = mic({ sampleRate: ctx.sampleRate, channels: 1, bitDepth: 16 })
 read((err, buf) => {
   if (err || !buf) return
-  src.pushData(buf, { channels: 1, bitDepth: 16 })
+  track.pushData(buf, { channels: 1, bitDepth: 16 })
 })
 ```
 
-`pushData()` accepts `Float32Array`, `Float32Array[]`, or interleaved 8/16/32-bit integer PCM buffers. Integer PCM conversion uses `pcm-convert`.
-
-With `web-audio-api/polyfill`, `navigator.mediaDevices.getUserMedia()` is also available and maps constraints to `audio-mic` options: `{ audio: { sampleRate, channelCount, sampleSize } }`.
+`track.pushData()` accepts `Float32Array`, `Float32Array[]`, or interleaved 8/16/32-bit integer PCM buffers. Integer PCM conversion uses `pcm-convert`. `CustomMediaStreamTrack` extends `MediaStreamTrack` — prior art: `CanvasCaptureMediaStreamTrack`.
 
 See [examples/mic.js](examples/mic.js) for a runnable demo with gain and VU meter. To record the graph to a buffer, use `OfflineAudioContext.startRendering()`. To capture live graph output as a stream, use `ctx.createMediaStreamDestination()`.
 </dd>
@@ -187,6 +192,23 @@ See [examples/mic.js](examples/mic.js) for a runnable demo with gain and VU mete
 import 'web-audio-api/polyfill'
 // AudioContext, GainNode, etc. are now global
 ```
+
+The polyfill also installs `navigator.mediaDevices.getUserMedia({ audio: true })`, backed by the optional [`audio-mic`](https://github.com/audiojs/audio-mic) peer dependency. This lets browser mic-capture code run verbatim in Node:
+
+```js
+import 'web-audio-api/polyfill'
+// npm install audio-mic
+
+const stream = await navigator.mediaDevices.getUserMedia({ audio: true })
+const ctx = new AudioContext()
+const src = ctx.createMediaStreamSource(stream)
+src.connect(ctx.destination)
+
+// stop capture
+stream.getAudioTracks()[0].stop()
+```
+
+Without `audio-mic` installed, `getUserMedia` rejects with a `NotFoundError` containing an install hint.
 </dd>
 
 <dt>Can I unit-test audio code?</dt>

examples/mic.js

@@ -5,7 +5,7 @@
 // Run: node examples/mic.js gain=0.8
 // Keys: space pause · + / - adjust gain · q quit
 
-import { AudioContext, MediaStreamAudioSourceNode } from 'web-audio-api'
+import { AudioContext, MediaStreamAudioSourceNode, MediaStream, CustomMediaStreamTrack } from 'web-audio-api'
 import mic from 'audio-mic'
 import { args, keys, status, clearLine, pausedTag } from './_util.js'
 
@@ -18,7 +18,10 @@ let bitDepth = parseInt($('bit', '16'))
 const ctx = new AudioContext({ sampleRate })
 await ctx.resume()
 
-const src = new MediaStreamAudioSourceNode(ctx, { numberOfChannels: channels, bitDepth })
+const track = new CustomMediaStreamTrack({ kind: 'audio', label: 'mic', settings: { channelCount: channels, sampleSize: bitDepth, sampleRate } })
+const stream = new MediaStream([track])
+
+const src = new MediaStreamAudioSourceNode(ctx, { mediaStream: stream })
 const gain = ctx.createGain()
 const analyser = ctx.createAnalyser()
 gain.gain.value = gainVal
@@ -28,7 +31,7 @@ src.connect(gain).connect(analyser).connect(ctx.destination)
 let read = mic({ sampleRate, channels, bitDepth })
 read((err, buf) => {
   if (err || !buf) return
-  src.pushData(buf, { channels, bitDepth })
+  track.pushData(buf, { channels, bitDepth })
 })
 
 let samples = new Float32Array(analyser.fftSize)

index.d.ts

@@ -270,6 +270,34 @@ export class MediaElementAudioSourceNode extends AudioNode {
   readonly mediaElement: any;
 }
 
+export class MediaStreamTrack extends EventTarget {
+  readonly id: string;
+  readonly kind: string;
+  readonly label: string;
+  enabled: boolean;
+  readonly readyState: 'live' | 'ended';
+  stop(): void;
+  clone(): MediaStreamTrack;
+  getSettings(): Record<string, any>;
+}
+
+export class CustomMediaStreamTrack extends MediaStreamTrack {
+  constructor(options?: { kind?: string; label?: string; settings?: Record<string, any> });
+  pushData(channelData: Float32Array | Float32Array[] | ArrayBuffer | ArrayBufferView, options?: { channels?: number; numberOfChannels?: number; bitDepth?: 8 | 16 | 32 }): void;
+  clone(): CustomMediaStreamTrack;
+}
+
+export class MediaStream extends EventTarget {
+  readonly id: string;
+  readonly active: boolean;
+  constructor(tracks?: MediaStreamTrack[] | MediaStream);
+  getTracks(): MediaStreamTrack[];
+  getAudioTracks(): MediaStreamTrack[];
+  getVideoTracks(): MediaStreamTrack[];
+  addTrack(track: MediaStreamTrack): void;
+  removeTrack(track: MediaStreamTrack): void;
+}
+
 // Error types
 export class InvalidStateError extends Error { readonly name: 'InvalidStateError' }
 export class NotSupportedError extends Error { readonly name: 'NotSupportedError' }

index.js

@@ -25,6 +25,7 @@ export { default as ScriptProcessorNode } from './src/ScriptProcessorNode.js'
 export { default as PannerNode } from './src/PannerNode/index.js'
 export { AudioWorkletNode, AudioWorkletProcessor } from './src/AudioWorklet.js'
 export { MediaStreamAudioSourceNode, MediaStreamAudioDestinationNode, MediaElementAudioSourceNode } from './src/MediaStreamAudioSourceNode.js'
+export { MediaStream, MediaStreamTrack, CustomMediaStreamTrack } from './src/MediaStream.js'
 export { default as AudioListener } from './src/AudioListener.js'
 export { BLOCK_SIZE } from './src/constants.js'
 export { InvalidStateError, NotSupportedError, IndexSizeError, InvalidAccessError, EncodingError } from './src/errors.js'

polyfill.js

@@ -1,71 +1,25 @@
 // Web Audio API globals for Node: `import 'web-audio-api/polyfill'`
-// Also exposes `navigator.mediaDevices.getUserMedia()` + MediaStream/Track so
-// browser mic code runs verbatim. Requires optional peer dep `audio-mic`.
+// Also exposes `navigator.mediaDevices.getUserMedia()` backed by the optional
+// peer dep `audio-mic` so browser mic code runs verbatim.
 import * as waa from './index.js'
-import convert from 'pcm-convert'
 
 for (let [name, value] of Object.entries(waa))
   if (typeof value === 'function' && !(name in globalThis)) globalThis[name] = value
 
 // Tone.js / standardized-audio-context checks `instanceof window.AudioParam`
 if (typeof window === 'undefined') globalThis.window = globalThis
 
-// --- MediaStream / MediaStreamTrack --------------------------------------
-// Minimal spec-shaped classes for `instanceof` + track.stop() in Node.
+globalThis.MediaStreamTrack ??= waa.MediaStreamTrack
+globalThis.MediaStream ??= waa.MediaStream
+globalThis.CustomMediaStreamTrack ??= waa.CustomMediaStreamTrack
 
-let nextId = 0
-class MediaStreamTrack extends EventTarget {
-  kind; label; enabled = true; readyState = 'live'
-  id = 'track-' + (++nextId)
-  #settings
-  constructor(kind = 'audio', label = '', settings = {}) {
-    super(); this.kind = kind; this.label = label; this.#settings = settings
-  }
-  stop() {
-    if (this.readyState === 'ended') return
-    this.readyState = 'ended'
-    this.dispatchEvent(new Event('ended'))
-  }
-  clone() { return new MediaStreamTrack(this.kind, this.label, this.#settings) }
-  getSettings() { return { ...this.#settings } }
-}
-
-class MediaStream {
-  id = 'stream-' + Math.random().toString(36).slice(2)
-  #tracks
-  _buffers = []
-  constructor(tracks = []) { this.#tracks = [...(tracks instanceof MediaStream ? tracks.getTracks() : tracks)] }
-  get active() { return this.#tracks.some(t => t.readyState === 'live') }
-  getTracks() { return [...this.#tracks] }
-  getAudioTracks() { return this.#tracks.filter(t => t.kind === 'audio') }
-  getVideoTracks() { return this.#tracks.filter(t => t.kind === 'video') }
-  addTrack(t) { if (!this.#tracks.includes(t)) this.#tracks.push(t) }
-  removeTrack(t) { let i = this.#tracks.indexOf(t); if (i >= 0) this.#tracks.splice(i, 1) }
-}
-
-globalThis.MediaStreamTrack ??= MediaStreamTrack
-globalThis.MediaStream ??= MediaStream
+globalThis.navigator ??= {}
+globalThis.navigator.mediaDevices ??= {}
 
 // --- navigator.mediaDevices.getUserMedia ---------------------------------
+// Backed by the optional 'audio-mic' peer dep.  Install: npm install audio-mic
 
 let pick = v => v == null ? undefined : typeof v === 'number' ? v : (v.ideal ?? v.exact ?? v.min ?? v.max)
-let splitPlanar = (data, channels) => {
-  if (channels === 1) return data
-  let frames = data.length / channels
-  return Array.from({ length: channels }, (_, ch) => data.subarray(ch * frames, (ch + 1) * frames))
-}
-
-let toFloat32 = (chunk, opts) => {
-  if (chunk instanceof Float32Array || Array.isArray(chunk)) return chunk
-  if (![8, 16, 32].includes(opts.bitDepth))
-    throw new TypeError('getUserMedia PCM conversion supports 8, 16, or 32-bit integer samples')
-  let bytes = chunk instanceof ArrayBuffer
-    ? chunk
-    : chunk.buffer.slice(chunk.byteOffset, chunk.byteOffset + chunk.byteLength)
-  let data = convert(bytes, { dtype: `int${opts.bitDepth}`, channels: opts.channels, interleaved: true, endianness: 'le' },
-    { dtype: 'float32', channels: opts.channels, interleaved: false })
-  return splitPlanar(data, opts.channels)
-}
 
 async function getUserMedia(constraints = {}) {
   if (!constraints.audio) throw Object.assign(new Error(
@@ -82,23 +36,44 @@ async function getUserMedia(constraints = {}) {
   if (![8, 16, 32].includes(opts.bitDepth)) throw Object.assign(new Error(
     'getUserMedia supports 8, 16, or 32-bit integer PCM samples in Node'),
     { name: 'NotSupportedError' })
+
   let read = mic(opts)
-  let track = new MediaStreamTrack('audio', 'Default audio input',
-    { sampleRate: opts.sampleRate, channelCount: opts.channels, sampleSize: opts.bitDepth })
-  let stream = new MediaStream([track])
-  let live = true
+  let track = new waa.CustomMediaStreamTrack({
+    kind: 'audio', label: 'Default audio input',
+    settings: { sampleRate: opts.sampleRate, channelCount: opts.channels, sampleSize: opts.bitDepth }
+  })
+  let stream = new waa.MediaStream([track])
+
   let pump = () => read((err, chunk) => {
-    if (!live || err || !chunk) return
-    stream._buffers.push(toFloat32(chunk, opts))
+    if (track.readyState === 'ended' || err || !chunk) return
+    track.pushData(chunk, { channels: opts.channels, bitDepth: opts.bitDepth })
     pump()
   })
   pump()
 
   let origStop = track.stop.bind(track)
-  track.stop = () => { live = false; try { read(null); read.close?.() } catch {} origStop() }
+  track.stop = () => {
+    // Best-effort mic close — errors here (e.g. already closed) are harmless.
+    try { read(null); read.close?.() } catch {}
+    origStop()
+  }
   return stream
 }
 
-globalThis.navigator ??= {}
-globalThis.navigator.mediaDevices ??= {}
-globalThis.navigator.mediaDevices.getUserMedia ??= getUserMedia
+const legacyGetUserMedia = typeof globalThis.navigator.getUserMedia === 'function'
+  ? globalThis.navigator.getUserMedia.bind(globalThis.navigator)
+  : undefined
+
+globalThis.navigator.mediaDevices.getUserMedia ??=
+  typeof legacyGetUserMedia === 'function'
+    ? (constraints) => new Promise((resolve, reject) => legacyGetUserMedia(constraints, resolve, reject))
+    : getUserMedia
+
+globalThis.navigator.getUserMedia ??= function (constraints, successCallback, errorCallback) {
+  Promise.resolve()
+    .then(() => globalThis.navigator.mediaDevices.getUserMedia(constraints))
+    .then(
+      (stream) => { if (typeof successCallback === 'function') successCallback(stream) },
+      (error) => { if (typeof errorCallback === 'function') errorCallback(error) }
+    )
+}