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PD ISO IEC TS 20071 — User Interface Component Accessibility Technical Specification Series (Audio Descriptions and Audio Presentation of Text in Videos)
Information Technology — User Interface Component Accessibility: Guidance on Audio Descriptions and Audio Presentation of Text in Videos (2015/2017 Editions)
🎧 PD ISO/IEC TS 20071 is the BSI-adopted ISO/IEC TS 20071 technical specification series for information technology — user interface component accessibility. The two parts in this batch are Part 21, which gives guidance on audio descriptions, and Part 25, which gives guidance on the audio presentation of text in videos, including captions, subtitles and other on-screen text. Both are handled by BSI Technical Committee ICT/-/6 (ICT Accessibility). The series provides operational guidance for accessible production of audiovisual media and digital content, supporting content producers, platforms, and accessibility consultants in implementing accessibility requirements such as the WCAG success criteria.
💡 Audio description is not “ordinary narration”: it describes visual information (actions, scenes, on-screen text) in concise language during the gaps in the original dialogue and sound effects, letting blind or low-vision users “see” the video. This series standardises how “information that cannot be seen” is spoken.
1. Series Composition and Scope 📌
| Standard | Title | ISO/IEC Edition | Core Content |
|---|---|---|---|
| PD ISO/IEC TS 20071-21:2015 | Information technology — User interface component accessibility — Part 21: Guidance on audio descriptions | ISO/IEC TS 20071-21 (Ed.1.0, 2015-12) | Application scenarios, writing principles, recording and synchronisation requirements |
| PD ISO/IEC TS 20071-25:2017 | Information technology — User interface component accessibility — Part 25: Guidance on the audio presentation of text in videos, including captions, subtitles and other on-screen text | ISO/IEC TS 20071-25 (Ed.1.0, 2017-02) | Presentation of on-screen text as audio: manner, timing and language requirements |
⚠️ This series is a technical specification (TS) giving operational accessibility-production guidance, not mandatory format constraints; concrete compliance requirements should follow WCAG 2.x success criteria and local regulations such as EN 301 549.
2. Part 21: Guidance on Audio Descriptions 🎙️
Audio description provides verbal descriptions of the visual content of a video for users with visual impairments. Key guidance of Part 21 includes:
- Application scenarios and audiences: when audio description is needed and which users it targets (blind, low-vision, cognitive impairments, etc.).
- Writing principles: selection of content to describe, concise and accurate language, and avoiding conflict with the original dialogue.
- Description timing and synchronisation: descriptions inserted in the gaps of original dialogue and sound effects, synchronised with visual events.
- Recording and delivery: recording quality, accent and speech rate, channel assignment (e.g., a separate audio track), and delivery requirements.
The quality of audio description directly determines whether vision-impaired users can obtain the complete information of a video; Part 21 provides producers with an actionable writing and production baseline.
3. Part 25: Guidance on the Audio Presentation of Text in Videos 📺
Videos frequently contain on-screen text such as captions, subtitles, titles, and chart labels. Part 25 specifies how to present such text in audio for users who cannot read the screen:
- Content to present: which on-screen text should be read aloud (e.g., captions, titles, key annotations).
- Manner of presentation: timing, speech rate, voice clarity, and whether a narration channel is used.
- Coordination with the original audio: how to schedule text narration between dialogue/sound effects to avoid overlap or omission of information.
- Language and localisation: consistency between the language of captions and the narration language, and multilingual handling.
✅ The combination of the two parts forms a complete “auditory accessibility” solution: Part 21 conveys “picture information”, while Part 25 conveys “on-screen-text information”, together allowing vision-impaired users barrier-free access to video content.
4. Summary of Key Technical Points 🔧
| Topic | Key Point | Document |
|---|---|---|
| Audience and scenarios | Blind, low-vision, cognitive impairment users | 20071-21 |
| Writing principles | Concise and accurate, avoid dialogue conflict | 20071-21 |
| Synchronisation | Insert in dialogue/sound gaps, synchronised with events | 20071-21 |
| Text presentation | Content and manner of reading captions, titles, labels | 20071-25 |
| Audio coordination | Timing and channel arrangement with original audio | 20071-25 |
| Language and delivery | Language consistency, multilingual, separate audio tracks | 20071-21 / -25 |
5. Engineering Practice 🛠️
- 🔍 Film and streaming production: add audio-description tracks and on-screen-text narration to post-production per this series.
- 🔧 Accessibility compliance: reference this series with WCAG/EN 301 549 to complete accessibility features for video content and satisfy regulatory requirements.
- 📊 Educational content: produce audio descriptions for online courses and training videos to support vision-impaired learners.
- 📋 Quality review: use this series as a benchmark to review the quality of audio descriptions and text presentation of published content within the content quality system.
6. Frequently Asked Questions ❓
❓ Q: What is the difference between audio description and ordinary narration?
A: Ordinary narration usually supplies background information or guides the story; audio description specifically describes visual information (actions, scenes, on-screen text) in the gaps of the original dialogue/sound effects, aiming to give vision-impaired users the information carried by the visual channel. Their functions and writing principles differ.
A: Ordinary narration usually supplies background information or guides the story; audio description specifically describes visual information (actions, scenes, on-screen text) in the gaps of the original dialogue/sound effects, aiming to give vision-impaired users the information carried by the visual channel. Their functions and writing principles differ.
❓ Q: How do captions and audio descriptions work together?
A: Captions usually serve deaf/hard-of-hearing users (turning sound into text), while audio descriptions serve vision-impaired users (turning pictures into sound). Part 25 further specifies turning text that appears in video — captions, titles, etc. — back into audio for users who cannot read the screen. Together the three cover different accessibility needs.
A: Captions usually serve deaf/hard-of-hearing users (turning sound into text), while audio descriptions serve vision-impaired users (turning pictures into sound). Part 25 further specifies turning text that appears in video — captions, titles, etc. — back into audio for users who cannot read the screen. Together the three cover different accessibility needs.
❓ Q: When should audio descriptions be inserted?
A: Use the natural gaps between original dialogue and sound effects (pauses, scene changes), describing visual events in sync while avoiding masking dialogue. If gaps are insufficient, compression or a secondary description track may be needed.
A: Use the natural gaps between original dialogue and sound effects (pauses, scene changes), describing visual events in sync while avoiding masking dialogue. If gaps are insufficient, compression or a secondary description track may be needed.
🔍 Q: How does this series relate to WCAG?
A: WCAG 2.x defines “success criteria” (e.g., 1.2.3 Audio Description, 1.2.5 Audio Description (Prerecorded)), forming the conformance-assessment framework; this series provides the operational guidance on how to actually create and implement those criteria — a supporting technical reference.
A: WCAG 2.x defines “success criteria” (e.g., 1.2.3 Audio Description, 1.2.5 Audio Description (Prerecorded)), forming the conformance-assessment framework; this series provides the operational guidance on how to actually create and implement those criteria — a supporting technical reference.