Specification

https://github.com/WebAudio/web-speech-api/pull/192

Explainer

https://github.com/WebAudio/web-speech-api/blob/main/explainers/speech-recognition-result-timestamps.md

Links

• The WG's request for this TAG review: https://github.com/WebAudio/web-speech-api/issues/191
• TAG review of the previous version of this specification, if any:
  • https://github.com/w3ctag/design-reviews/issues/1093 (MediaStreamTrack input)
  • https://github.com/w3ctag/design-reviews/issues/1146 (On-device speech recognition options)
• A description of what has changed since our previous review: https://github.com/WebAudio/web-speech-api/pull/192

Feature 1:

• Previous early design review, if any: N/A
• An introduction to the feature, aimed at unfamiliar audiences: https://github.com/WebAudio/web-speech-api/blob/main/explainers/speech-recognition-result-timestamps.md
• A description of the problems that end-users were facing before this proposal: https://github.com/WebAudio/web-speech-api/blob/main/explainers/speech-recognition-result-timestamps.md#problem
• Alternatives considered: https://github.com/WebAudio/web-speech-api/blob/main/explainers/speech-recognition-result-timestamps.md#alternatives-considered
• Examples of how to use the proposal to solve the end-users' problems: https://github.com/WebAudio/web-speech-api/blob/main/explainers/speech-recognition-result-timestamps.md#proposed-behavior--example-usage
• What do the end-users experience with this proposal: End users experience synchronized, real-time captions and translated subtitles during live video conferencing and media playback. Web applications can detect when on-device ASR models lag behind real-time on resource-constrained devices and automatically transition to cloud backends without user disruption.
• User research you did to validate the problem and/or design, if any: Live conferencing latency studies and interactive validation demo: https://michaelwasserman.github.io/web-speech-demos/speech_latency_h.html
• Web Platform Tests: https://github.com/web-platform-tests/wpt/tree/master/speech-api (specifically idlharness.https.window.js and SpeechRecognition-onresult-manual.https.html)

The specification

• Follows the Web Platform Design Principles.
• Includes Security and Privacy Considerations sections based on answers to the Security/Privacy Questionnaire.

Where and by whom is the work is being done?

• GitHub repo: https://github.com/WebAudio/web-speech-api
• Primary contacts:
  • Alan Ding (@alan33d), Google, Spec Editor / Implementer
  • Evan Liu (@evanbliu), Google, Spec Editor
  • Paul Adenot (@padenot), Mozilla, WebAudio WG Member / Spec Editor
  • Hongchan Choi (@hoch), Google, WebAudio WG Member / Spec Editor
• Organization/project driving the specification: Google / Chromium
• This work is being funded by: Google
• Primary standards group developing this feature: Audio Working Group (WebAudio WG) / Audio Community Group (AudioCG)
• Incubation and standards groups that have discussed the design:
  • Audio Working Group: https://github.com/WebAudio/web-speech-api/issues/191, https://github.com/WebAudio/web-speech-api/pull/192

Feedback so far

• Active horizontal reviews: https://github.com/WebAudio/web-speech-api/blob/main/explainers/speech-recognition-result-timestamps.md#security-and-privacy-considerations
• Multi-stakeholder feedback:
  • Chromium comments: Positive / In active development (https://chromestatus.com/feature/5811907077472256)
  • Mozilla comments: Active discussion in https://github.com/WebAudio/web-speech-api/issues/191 and https://github.com/WebAudio/web-speech-api/pull/192#discussion_r3774155900 by @padenot (provided guidance on using double in seconds and non-nullable attributes to match Web Audio conventions).
  • WebKit comments: Standards position to be filed at https://github.com/WebKit/standards-positions/
• Major unresolved issues with or opposition to this specification: None. Consensus reached on using non-nullable double representing seconds relative to audio stream start.
• Status/issue trackers for implementations:
  • Chrome Status: https://chromestatus.com/feature/5811907077472256
  • Chromium Issue Tracker: https://issues.chromium.org/issues/528037568

You should also know that...

W3C Audio WG/CG Meeting Discussion: This feature was presented and discussed during the W3C Audio WG/CG Teleconference on August 13, 2026 (see Meeting Minutes). The group aligned on developer needs for audio timeline association and on-device ASR latency tracking (e.g. enabling optional failover to a cloud ASR provider, to prevent stale or delayed captions in live video conferencing).

• Mozilla's feedback in PRs were also discussed and addressed during the meeting.
• An interactive demonstration showcasing real-time latency calculation, subtitle synchronization, and the inadequacy of existing coarse DOM event timestamps was also presented at the WG meeting. The demo is available at: https://michaelwasserman.github.io/web-speech-demos/speech_latency_h.html

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