Simplify media stream implementation by dy · Pull Request #101 · audiojs/web-audio-api

dy · 2026-04-29T22:32:15Z

Based on #35 (comment)

This is much closer to a standard implementation of MediaStreamTrack and MediaStream.

Here's why:

EventTarget Extension: Standard web APIs like MediaStreamTrack and MediaStream inherit from EventTarget. Both classes now explicitly extend EventTarget.
State Properties: MediaStreamTrack has standard read-only properties (id, kind, label, readyState) and enabled flag.
Methods: Added standard clone(), getSettings(), stop(), getTracks(), getAudioTracks(), getVideoTracks(), addTrack(), removeTrack().
Separation of Concerns: The stream data source logic (pushData) now lives appropriately on the MediaStreamTrack, mirroring how audio capture happens on a track level natively, rather than on the MediaStreamAudioSourceNode directly.

The tests run successfully with this refactored, more standards-compliant implementation.

k2d222

See comment, otherwise LGTM 👍

k2d222 · 2026-04-30T09:41:52Z

 await ctx.resume()

-const src = new MediaStreamAudioSourceNode(ctx, { numberOfChannels: channels, bitDepth })
+const track = new MediaStreamTrack('audio', 'mic', { channelCount: channels, sampleSize: bitDepth, sampleRate })


This makes a lot more sense, but I would make this a subclass of MediaStreamTrack. In the WebAudio spec, MediaStreamTrack has no public constructor, and no pushData method. But you can freely extend the spec by creating a CustomMediaStreamTrack type, that has a public constructor and the push method. There is prior art with CanvasCaptureMediaStreamTrack.

For the parameters, I would provide just one in an object, because it's not clear what the first two parameters are for (track kind, and track label). In short:

const track = new CustomMediaStreamTrack({ kind: 'audio', label: 'track from audio-mic', settings: { channelCount, sampleSize, bitDepth } });

Good point, added.
Do you think CustomMediaStreamTrack is fine name? It's not immediately reflective of its purpose.

Copilot

Pull request overview

This PR refactors the media-stream side of the library to expose explicit MediaStream/MediaStreamTrack classes, move PCM ingestion onto a new CustomMediaStreamTrack, and align the microphone example/docs with that new flow. It fits into the codebase by reshaping how MediaStreamAudioSourceNode interoperates with Node-side audio capture.

Changes:

Add exported MediaStream, MediaStreamTrack, and CustomMediaStreamTrack classes plus TypeScript declarations.
Rework MediaStreamAudioSourceNode to read queued audio from a track instead of accepting pushData() directly.
Update the polyfill, tests, example microphone app, and README to use the new custom-track-based capture path.

Reviewed changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
`test/polyfill.test.js`	Updates polyfill tests for new globals and custom track behavior.
`test/MediaStreamNodes.test.js`	Reworks media stream node tests to feed audio through `CustomMediaStreamTrack`.
`src/MediaStreamAudioSourceNode.js`	Moves source-node input handling to track-backed buffers and keeps destination-node track creation in sync.
`src/MediaStream.js`	Introduces the new MediaStream/track implementations and PCM normalization logic.
`polyfill.js`	Simplifies globals installed by the Node polyfill.
`index.js`	Exports the new media stream classes from the package root.
`index.d.ts`	Updates public typings for the new media stream API surface.
`examples/mic.js`	Migrates the microphone demo to push PCM into a custom track.
`README.md`	Rewrites microphone capture guidance around `CustomMediaStreamTrack`.

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Copilot reviewed 8 out of 10 changed files in this pull request and generated 6 comments.

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dy · 2026-05-02T03:48:24Z

@copilot apply changes based on the comments in this thread

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Pull request overview

Copilot reviewed 8 out of 10 changed files in this pull request and generated 7 comments.

Comments suppressed due to low confidence (1)

src/MediaStreamAudioSourceNode.js:115

createMediaStreamDestination().stream is still a plain object here instead of an instance of the new MediaStream class. That means destination streams do not participate in the EventTarget-based API added by this PR (instanceof MediaStream, stream events, etc.), so callers now get two incompatible "MediaStream" shapes depending on where the stream came from.

    this.#stream = {
      get _buffers() { return track._buffers },
      read() { return track._buffers.shift() || null },
      get readable() { return track._buffers.length > 0 },
      getTracks: () => [track],
      getAudioTracks: () => [track],
      getVideoTracks: () => [],
    }

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…docs to README Agent-Logs-Url: https://github.com/audiojs/web-audio-api/sessions/21dacecc-c458-4c59-9617-29c97ae5ac2c Co-authored-by: dy <300067+dy@users.noreply.github.com>

Copilot · 2026-05-02T12:08:59Z

@copilot apply changes based on the comments in this thread

The last outstanding item from that review was the strong-reference ended listener in clone() (introduced after 526c715). Fixed in a2e5755: the listener that closed over clone directly has been removed. Per-spec, clones are independent tracks and callers stop them separately; _pushNormalized now lazily prunes clones whose readyState === 'ended', so explicitly-stopped clones no longer receive data and are removed from the fan-out set without needing any listener.

dy · 2026-05-02T13:32:22Z

@copilot CI fails, please fix

… fix WPT silence-detector test Agent-Logs-Url: https://github.com/audiojs/web-audio-api/sessions/0daa36f8-3469-425c-89fa-365d5fb40d2c Co-authored-by: dy <300067+dy@users.noreply.github.com>

Copilot · 2026-05-02T13:38:33Z

@copilot CI fails, please fix

Fixed in 2515659. The WPT test mediastreamaudiosourcenode-from-context-with-different-rate was failing because MediaStreamAudioSourceNode._tick() returned a zero-filled buffer when the track ended but never set this._ended = true. AudioWorkletNode checks _ended on its sources before each quantum — only when _ended = true does it pass an empty inputs[0] to the worklet's process(), making hasInput = false. Added this._ended = false in the constructor and this._ended = true in _tick() when track.readyState === 'ended'.

Simplify implementation

d59a62e

k2d222 reviewed Apr 30, 2026

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Make safer CustomMediaStreamTrack

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fix: CustomMediaStreamTrack.clone() shares _buffers with original

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fix: enforce track lifecycle in pushData and _tick

d0cd67a

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fix: use CustomMediaStreamTrack in destination node so clone() shares…

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fix: cache track in source node; fan-out clone pattern with auto-cleanup

94d8f19

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fix: restore audio-mic-backed getUserMedia in polyfill; fix stray fra…

12cd5e0

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fix: remove strong-ref ended listener from clone(); add getUserMedia …

a2e5755

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fix: set _ended=true on MediaStreamAudioSourceNode when track ends to…

2515659

… fix WPT silence-detector test Agent-Logs-Url: https://github.com/audiojs/web-audio-api/sessions/0daa36f8-3469-425c-89fa-365d5fb40d2c Co-authored-by: dy <300067+dy@users.noreply.github.com>

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dy merged commit e162cbc into master May 2, 2026

dy deleted the mic branch May 2, 2026 13:43

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