# News from the W3C

_A transmission from the Web standards side_

Paul Adenot, mozilla

Web Audio Conference — IRCAM, Paris

2025-11-21

---

# Me ?

Mozilla + W3C

---

# Agenda

New in an audio-related spec...

...new in a non-audio-related spec

---

# A bit about the W3C

- Consortium

- Browser vendors but not only!

- Universities, research labs, companies, governments...

---

# Group types

- **Working groups**: **can** publish standards, patent policy, requires (paid) membership, or to be an invited expert

- **Community group**: **cannot** publish standards, no patent policy, free + easy to join, often incubates texts that will become standards later

- **Interest group**: **cannot** publish standards, free + easy to join, produces "notes" that are often input to standards documents.

---

# In our field(s)

- **Audio Working Group**: publishes the Web Audio API, Web MIDI API, soon the Web
  Speech API (Speech recognition & synthesis)

- **Media Working Group**: publishes MSE, EME, Web Codecs, various other items
  such as autoplay policies, etc.

- **Web Real-time communication working group**: WebRTC networky things (but not
  protocols, done by IETF), `MediaStream` things, audio input (historical)

---

# Outside our field

- **Web Transport Working Group**: Web Transport (!)

- **Web Assembly Working Group**: Web Assembly (!!)

- ...lots of other groups

---

# Outside W3C

- **WHATWG**: mostly HTML and DOM (e.g. `HTMLMediaElement`)

- **TC39**: EcmaScript

- **IETF**: networky things

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# Join the CG

A couple clicks, participate to a~~n~~ ~~exciting~~ monthly online meeting

<https://www.w3.org/community/audio-comgp/>

---

# This year in the Audio Working Group

- Web Audio API
 - Web MIDI API
 - Web Speech API NEW

---

# Web Audio API implementations

Total count of complete & independant implementations: 6.5

- In **browsers**: Gecko, WebKit, Blink, ~~Edge~~

- **Stand-alone**: `web-audio-api-rs`, Netflix's (proprietary)

- Partial: `react-native-audio-api`

---

# Testing

Anybody can contribute tests!

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# New features

- `AudioContext` `"interrupted"` state
  - New `MessagePort` on the global
  - Audio playout stats
  - High-resolution timestamps
  - Render quantum size selection

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# AudioContext Interrupted State

- Enables browsers to **pause or resume audio** during system interruptions
    (e.g., phone call, lid close, exclusive hardware use)
  - Origin trial in Chromium underway

Approved

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# `MessagePort` on the global

```webidl
  [Global=(Worklet,AudioWorklet),Exposed=AudioWorklet]
  interface AudioWorkletGlobalScope : WorkletGlobalScope {
    [Throws]
    undefined registerProcessor (DOMString name, AudioWorkletProcessorConstructor processorCtor);
    readonly  attribute   unsigned long long currentFrame;
    readonly  attribute   double currentTime;
    readonly  attribute   float sampleRate;
    readonly  attribute   MessagePort port;
  };
  ```

←

No need to create a "dummy" `AudioWorkletNode` to set things up!

---

# Audio Playout Stats API

- New API for monitoring audio quality metrics
    - Glitch counts
    - Statistics about latency
  - Anti-fingerprinting measures under discussion

```webidl
  interface AudioPlaybackStats {
    readonly attribute double underrunDuration;
    readonly attribute unsigned long underrunEvents;
    readonly attribute double totalDuration;
    readonly attribute double averageLatency;
    readonly attribute double minimumLatency;
    readonly attribute double maximumLatency;
    undefined resetLatency();
    [Default] object toJSON();
  };

partial interface AudioContext {
    [SameObject] readonly attribute AudioPlaybackStats playbackStats;
  };
  ```

Under review

---

# High-Resolution Timing

Finally!

- `performance.now()` exposed in `AudioWorklet`
  - Needed for **accurate performance measurement**
  - Dedicated TPAC 2025 meeting planned last week

Fingerprinting protection: lowest granularity with in Cross Origin Isolated
  documents, same as `SharedArrayBuffer`

<span style="color: green; transform: rotate(-20deg); font-size: 3.4em;border:
 10px solid green; position: absolute; top: 3.3em; left: 10px;font-weight:
 700;background-color: rgba(255, 255, 255, 0.9);">Easy to implement

---

# High-Resolution Timing

Finally!

- `performance.now()` exposed in `AudioWorklet`
  - Needed for **accurate performance measurement**
  - Dedicated TPAC 2025 meeting planned last week

Fingerprinting protection: lowest granularity with in Cross Origin Isolated
  documents, same as `SharedArrayBuffer`

<span style="color: green; transform: rotate(-20deg); font-size: 3.4em;border:
 10px solid green; position: absolute; top: 3.3em; left: 10px;font-weight:
 700;background-color: rgba(255, 255, 255, 0.9);"><s>Easy to implement</s>

<span style="color: green; transform: rotate(5deg); font-size: 4.4em;border:
 10px solid green; position: absolute; top: 2.0em; left: 30px;font-weight:
 700;background-color: rgba(255, 255, 255, 0.9);">Implemented

---

# Render quantum

Allow breaking free of the 128-frames block size.

Higher or lower latency, or more importantly, aligned on the native block
  size.

Hard to implement

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# Web MIDI API

New editor, spec changes underway, no big implementation change...

... except prompt + secure origin required.

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# Non-Audio WG specs

... that we use and rely on

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# Web Codecs

Not too recent, but important for us audio developers.

- `f32-planar` sample format required (mandatory to implement)

- `u8`, `s16`, `s24` — planar AND interleaved (supported everywhere)

- BYOD BHTD (`libavcodec` for the Web, **not** `libavformat`)

- Low level, composes well with other APIs on the Web Platform

- Much better than `decodeAudioData(...)`, easy to use

No excuse

---

# Web Speech API

- Adopted by the Audio Community Group

- Will likely be adopted as a Audio Working Group deliverable next
  rechartering

- **Local** recognition

- **Low-latency** (< 1000ms)

- `MediaStream`-based, compatible w/ the Web Audio API

- High quality low-latency local speech synthesis up next !

Soon

---

# Web Transport

Low latency client-server (for now) communication, good for real time!

Low-latency, bidirectional, reliable or unreliable data transport over HTTP/3

Some excuses

<span style="color: green; transform: rotate(-15deg); font-size: 4.8em;border:
 10px solid green; position: absolute; top: 2.5em; left: 30px;font-weight:
 700;background-color: rgba(255, 255, 255, 0.9);">Not for long!

---

# `WASM`

- Memory64

- Multi-memory

- `WASM gc`

- Tail call optimizations

No excuse

<span style="color: red; transform: rotate(25deg) scale(0.95); font-size: 3.4em;border:
 10px solid red; position: absolute; top: 2.3em; left: 10px;font-weight:
 700;background-color: rgba(255, 255, 255, 0.9);">No GC on the audio thread
 though

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# `Atomics`

- `waitAsync`

- Relaxed SIMD

<span style="color: red; transform: rotate(25deg) scale(0.95); font-size: 5.4em;border:
 10px solid red; position: absolute; top: 2.0em; left: 10px;font-weight:
 700;background-color: rgba(255, 255, 255, 0.9);">Be careful

---

# Thanks !

<dl>
 <dt>
 Slides
 </dt>
 <dd>
 <a
 href="https://padenot.github.io/wac-25/">https://padenot.github.io/wac-25/</a> 
 </dd>
 <dt>Email</dt>
 <dd><a
 href="mailto:padenot@mozilla.com"><code>padenot@mozilla.com</code></a></dd>
 </dl>