Morgan Peck

Captions are essential for making audio and video content accessible to everyone. They’re text-based versions of spoken content that display synchronized with the audio, ensuring that all users—regardless of hearing ability—can access your multimedia content.

This comprehensive guide covers everything you need to know about creating effective, accessible captions that meet WCAG standards and provide an excellent user experience.

Who Benefits from Captions?

Captions help far more people than you might expect:

People who are deaf or hard of hearing: Captions provide access to audio content they otherwise couldn’t perceive.

Non-native speakers: Captions help people learning a language follow along and improve comprehension.

People in sound-sensitive environments: Users in libraries, offices, or public spaces can watch videos without disturbing others.

People in noisy environments: Captions make content accessible on buses, trains, or busy locations where audio is difficult to hear.

People who process information better visually: Some users simply prefer reading along while listening to reinforce understanding.

Search engines: Captions provide searchable text content, improving SEO and content discoverability.

Captions vs. Subtitles

While often used interchangeably, captions and subtitles serve different purposes:

Captions:

Designed for people who are deaf or hard of hearing
Include spoken dialogue and sound descriptions
Describe important audio information (music, sound effects, speaker identification)
Assume the viewer cannot hear the audio

Subtitles:

Designed for people who can hear but don’t understand the language
Provide translation of dialogue only
Assume the viewer can hear sound effects and music
Focus solely on spoken words

For accessibility, you need captions, not just subtitles.

Open Captions vs. Closed Captions

Open Captions

Open captions are permanently embedded (“burned in”) to the video during production. They’re always visible and cannot be turned off.

Advantages:

Work with any media player
Guaranteed to be visible
No need for caption file support
Ideal for presentations and conferences

Disadvantages:

Cannot be turned off
Cannot be customized by users
Require separate video files for different languages

Closed Captions

Closed captions are separate text files synchronized with the video. Users can toggle them on and off.

Advantages:

Users control visibility
Can be customized (size, color, position)
Support multiple languages with one video file
Can be updated without re-encoding video

Disadvantages:

Require media player support
Depend on proper file formatting
May not display if files are missing or incompatible

Recommendation: Use closed captions for online videos where users have player controls. Use open captions for presentations, conferences, or situations where you can’t guarantee caption support.

What to Include in Captions

Required Elements (WCAG 2.1 AA)

Verbatim dialogue for scripted content: Include all spoken words exactly as said, including filler words like “um” and “uh” for scripted content. This preserves the intended delivery and timing.

All off-screen speech: Capture any dialogue spoken by people not visible on screen.

Speaker identification: Identify speakers when:

It’s not obvious who’s speaking
The speaker is off-screen
Multiple people are speaking
Context doesn’t make it clear

Background sounds: Describe important sounds using [brackets] or (parentheses):

[phone ringing]
[door slams]
[applause]

No spoilers: Don’t reveal information before it’s meant to be known. Captions should maintain the same suspense and pacing as the audio.

Highly Recommended (WCAG Best Practices)

Conventional spelling: Use standard spelling, not phonetic. Write “going to” not “gonna” unless phonetic spelling is essential to meaning.

Sound descriptions: Describe sounds by what they are, not what causes them:

Good: [thunder]
Avoid: [storm approaching]

Punctuation for emphasis: Use proper punctuation to convey tone. Avoid adding extra words to explain emphasis.

Music identification: Identify music by title and artist when appropriate and relevant to content.

Important lyrics: Include relevant lyrics verbatim, set off with music notes (♪):

♪ Happy birthday to you ♪

Inaudible speech: When speech is unclear, note it neutrally:

[inaudible]
[unclear]

Avoid judgmental terms like “unintelligible.”

Whispered or mouthed speech: Indicate the manner of speaking:

(whispering): I can’t believe it
(mouthing): Are you okay?

Retain strong language: Don’t censor captions unless the audio is also censored. Match the content’s intended audience.

Discretionary Elements

Unscripted content: For live broadcasts, documentaries, and interviews, captions should be verbatim but may omit excessive filler words that impair readability. Balance accuracy with ease of reading.

Visual Presentation Guidelines

Text Display

Line limits:

Maximum 3 lines per caption
Prevents blocking important visual content
Improves reading speed and comprehension

Character limits:

Maximum 32 characters per line
Ensures readability at standard viewing distances

Line breaks: Insert breaks at logical points between phrases, not mid-sentence:

Good:
I never thought
I'd see you again.

Bad:
I never thought I'd
see you again.

Sentence breaks: Split longer sentences at natural grammatical breaks (conjunctions, prepositions, articles):

Good:
The meeting was postponed
because the CEO was traveling.

Bad:
The meeting was postponed because
the CEO was traveling.

Typography

Case: Use mixed case (standard capitalization) for better readability. AVOID ALL CAPS except for emphasis or titles when appropriate.

Font:

Default to sans-serif fonts
Normal weight (not bold—harder to read)
Avoid decorative or script fonts

Titles: Use quotation marks and standard capitalization for titles:

“The Great Gatsby”
“Bohemian Rhapsody”

Emphasis:

Use italics for emphasis when punctuation isn’t sufficient
Use ALL CAPS sparingly for strong emphasis only
Prioritize punctuation over formatting

Color and Contrast

Default styling:

Black background with white text
Provides maximum contrast and readability

Minimum contrast: 3:1 contrast ratio between text and background for 18pt font or larger

Color for meaning: Never use color alone to convey information. Always provide text-based alternatives for users who are colorblind.

Customization: Media players should allow users to customize caption appearance (color, size, font, background).

Timing and Synchronization

Display duration:

Minimum 2 seconds on screen
Allow 0.3 seconds per word when possible
Add extra time for unfamiliar or complex words
Add extra time when visuals are complex or busy

Synchronization: Captions must be precisely synchronized with audio, appearing when words are spoken.

Silent intervals:

Remove captions after 4-5 seconds of silence
Leave 1.5 seconds minimum between captions to prevent jerky visual effects
Note periods of silence when visuals suggest important audio: [silence]

Positioning: Position captions to avoid obscuring:

On-screen text
Faces and expressions
Important visual information

Caption File Formats

Caption files contain all spoken words, sound descriptions, and time codes indicating when captions should appear.

Basic Formats

SubRip (.srt):

Most widely supported format
Simple text-based format
Limited styling options
Good compatibility across players

SubViewer (.sbv, .sub):

Basic format with simple timing
Limited player support

LRC (.lrc):

Common for music lyrics
Basic timing support

Advanced Formats

WebVTT (.vtt):

Modern web standard
Supports styling and positioning
Allows user customization
Growing player support
Recommended for web content

SAMI (.smi, .sami):

Supports styling
Good for multiple languages
Declining support

TTML (.ttml):

Advanced styling capabilities
XML-based format
Good for broadcast standards

Format Recommendations

Always provide WebVTT when possible:

Allows users to set caption preferences in their operating system
Settings apply consistently across browsers and videos
Future-proof format with growing adoption

Provide multiple formats when necessary:

Different players support different formats
Include .srt for maximum compatibility
Include .vtt for modern features and user customization

Caption Quality Checklist

Before publishing your captions, verify:

Conclusion

Effective captions make your audio and video content accessible to millions of users who rely on them. While creating quality captions requires attention to detail, the impact is significant—you’re ensuring equal access to information, entertainment, and education.

Key takeaways:

Captions benefit many users beyond those who are deaf or hard of hearing
Use closed captions for online content with player controls
Include all dialogue, speaker identification, and important sounds
Follow visual presentation guidelines for readability
Provide captions in WebVTT format when possible
Test captions for timing, accuracy, and synchronization

Remember: Captions aren’t just a compliance checkbox—they’re a fundamental accessibility feature that improves the experience for all users. Invest the time to create quality captions, and you’ll create content that truly works for everyone.

Resources

For creating and editing caption files:

Amara - Free online caption editor
YouTube Studio - Automatic captions with editing tools
Subtitle Edit - Free desktop software for Windows
Aegisub - Advanced subtitle editing software

For caption validation:

WebVTT Validator - Check file format correctness
Caption testing with screen readers
User testing with people who rely on captions

Captions for Video and Audio Content