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, frame-accurate captions and translated subtitles during media playback and live conferencing, interactive "click-to-seek" transcript navigation, and seamless alignment between speech transcripts and recorded media tracks.
• User research you did to validate the problem and/or design, if any: Live conferencing / media synchronization studies and interactive validation demos:
  • Live Meeting Caption Sync & Recording Demo: https://alan33d.github.io/web-speech-demos/live_meeting_recording_demo.html
  • WebRTC Caption Playout Delay Test: https://alan33d.github.io/web-speech-demos/webrtc_caption_sync_test.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, non-nullable attributes, and naming speechStartTime/speechEndTime to mirror speechstart/speechend).
  • 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, named speechStartTime and speechEndTime.
• 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 media timeline association (e.g. generating VTTCue captions, click-to-seek transcripts, and synchronizing captions with recorded video).

• Mozilla's feedback in PRs was also discussed and addressed during the meeting.
• Interactive demonstrations showcasing subtitle synchronization, recording timeline alignment, and the inadequacy of existing coarse DOM event timestamps were presented at the WG meeting and are available for testing:
  • https://alan33d.github.io/web-speech-demos/live_meeting_recording_demo.html
  • https://alan33d.github.io/web-speech-demos/webrtc_caption_sync_test.html

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