After exploring the Level A criteria for prerecorded media, let's now move to a more demanding and specific requirement for real-time content: Success Criterion 1.2.4: Captions (Live). This is a Level AA criterion, which reflects the added complexities associated with providing captions for live events.
What does Criterion 1.2.4 require?
Criterion 1.2.4 states that for all live audio content (and live video content with significant audio), captions must be provided.
- Live Content: Refers to content presented in real-time, such as webcasts, webinars, online meetings, live sports events, live news broadcasts, or streaming events. The key characteristic is that it is not prerecorded and thus cannot be edited or reviewed before presentation.
- Captions: As with Criterion 1.2.2, captions are the textual representation of all audio (dialogue and significant non-speech sounds) and must be synchronized with the content.
Providing live captions is crucial for deaf or hard of hearing individuals who wish to participate in real-time events. Without captions, access to live conferences, lectures, meetings, or news is severely impaired. The move to Level AA reflects the greater effort and accuracy required to provide this service in real-time, ensuring a complete user experience.
Key Requirements and Challenges of Live Captioning:
1. Real-time Synchronization: Captions must appear almost simultaneously with the audio. A small delay is inevitable but must be minimized to maintain context.
2. Accuracy: Given the "live" nature, achieving 98-99% accuracy (often considered the standard for quality captions) is a significant challenge. Errors or omissions can alter meaning.
3. Completeness: They must include both speech and relevant non-verbal sounds, although the speed and complexity of a live event can make it difficult to capture every nuance.
4. Reliability: The captioning system must be robust and stable to prevent interruptions during the event.
Methods and Technologies for Live Captioning:
1. Human Transcription (CART - Communication Access Realtime Translation / Respeaking):
- CART: A specialized captioner (stenographer) types audio in real-time, often with incredible speed and high precision.
- Respeaking: A captioner repeats the dialogue into a microphone to a speech recognition software, which then generates the captions.
- Advantages: Higher accuracy, better handling of accents, technical jargon, and overlapping speech.
- Disadvantages: High cost, limited availability.
- How it works: AI software transcribes audio in real-time.
- Advantages: Lower cost, immediate availability, scalability.
- Disadvantages: Variable accuracy (sensitive to accents, background noise, complex terminology), punctuation errors, and speaker identification issues. Often requires post-editing or human monitoring.
- Recommended Use: For less critical situations or as a basis for human correction.
- Audio Quality: Clear audio is paramount for any live captioning method.
- Planning: For important events, plan for human captioners or well-configured and tested ASR systems.
- Training: If using internal captioners or managing the process, training is crucial.
We invite the community to share their experiences:
- What technologies or services have you used for live captioning?
- What have been the biggest challenges you've faced in ensuring real-time accuracy?
- Do you have any tips for improving the quality of automatic captions?
Warm regards,
Michele (wcgadmfrm)
WCAG Plus Forum Team