Captions ensure that spoken words, sound effects, and other meaningful sounds are presented synchronised with the video as it plays.
WCAG Success Criterion:
1.2.4 Captions (Live) – Level AA
All live video content that includes audio must provide captions that are synchronised with the audio in real time.
What Is a Live Caption
Live captions are real-time text alternatives for audio content in synchronised media such as live broadcasts, webcasts, or online events.
They display spoken dialogue, identify speakers, and describe important sounds like applause or background music.
Without Captions
Without live captions, people who cannot hear the audio will miss what is being said or what sounds are happening.
They may see a speaker talking or music playing, but will not know the words or sounds being conveyed.
How to Fix the Problem
To make live video accessible, provide synchronised text for all audio content during the live event.
This ensures that users can follow the content as it happens.
You can provide live captions in one of the following ways.
Correct Implementation Examples
Using Real-time Captioning Services
A live event uses Communication Access Realtime Translation (CART) or another real-time captioning service to transcribe spoken words and sounds as they occur.
Using Automated Captions with Review
A live broadcast platform enables automatic captions that are monitored by a human captioner to maintain accuracy and timing.
Using Integrated Caption Tools
A video streaming platform includes built-in captioning tools, allowing hosts to enable captions during live sessions.
Incorrect Implementation Examples
These examples fail accessibility testing because they do not provide real-time synchronised captions.
- A live video stream with no captions
- Captions added only after the event ends
- Captions that are delayed or not synchronised with the audio
- Captions that omit non-speech information (for example, background sounds or speaker identification)
All of these examples leave viewers who rely on captions without a full understanding of the live content.
Why This Matters
When live audio lacks captions, some users miss essential information.
A person who is deaf might see a presenter talking but not know what is being said.
With proper live captions, they can read:
“Anchor: Heavy rainfall expected tonight.”
“[Music playing softly in the background]”
This ensures equal access to information as it happens.
Rule Description
All live video content that includes audio must have captions synchronised in real time.
Captions should:
- Accurately represent spoken words and sounds
- Identify speakers when necessary
- Be synchronised with the audio track
Simplified Algorithm
- Identify all live videos that include audio.
- Check if captions are provided and synchronised in real time.
- Verify that captions include:
- Spoken dialogue
- Speaker identification (if relevant)
- Non-speech sounds that convey meaning
- If captions are missing, delayed, or incomplete → fail the rule.
Quick Reference Table
| Type | Example | Pass/Fail |
|---|---|---|
| Real-time human captions (CART) | Live broadcast with real-time captions | ✅ |
| Automated captions with review | AI-generated captions monitored by a captioner | ✅ |
| Captions added after broadcast | Uploaded only after the live event | ❌ |
| No captions | No text alternative for audio | ❌ |
| Captions missing sound cues | Dialogue shown, but no sound descriptions | ❌ |
Wrapping Up
Every live video that includes audio must provide captions that are accurate, synchronised, and comprehensive.
Captions help people who are deaf or hard of hearing understand and engage with real-time content.
Always ensure that:
- Captions are displayed as the event happens
- Spoken words and sounds are represented clearly
- Speaker names or sound effects are included when meaningful
Without live captions, important parts of the experience remain inaccessible, even though the video is visible to everyone.
