WCAG Caption Checker
Accessibility validation, built in
Vosuba automatically validates your subtitles against WCAG 2.2 AA, ADA, and FCC standards. Flag reading-speed violations, fix them with one click, and add SDH sound labels — all before you export.
What Vosuba checks
CPS (Characters Per Second)
Flags subtitle segments that exceed your target reading speed. Default threshold: 15 CPS (WCAG recommended). Configurable from 10–25 CPS depending on your audience. Segments in violation are highlighted in the timeline.
Minimum Display Duration
Ensures no subtitle segment is displayed for less than 1 second — the minimum recommended by WCAG and FCC. Flash-speed captions are flagged and can be auto-extended.
Line Length & Line Count
Checks that no segment exceeds 2 lines or 42 characters per line (broadcast standard). Long segments are flagged for splitting into readable chunks.
Sound Detection (SDH)
AI detects 60+ non-speech sounds (music, applause, door slams, phone rings) and inserts SDH labels following DCMP guidelines. Essential for deaf and hard-of-hearing viewers.
Speaker Identification
Diarization detects speaker changes and labels them in the subtitle track. WCAG recommends identifying speakers in multi-person content for comprehension.
Compliance Dashboard
A single view showing your project's accessibility score across all checks. See exactly which segments pass or fail — then fix them inline or with the one-click auto-fix.
⚡ One-Click Auto-Fix
Vosuba doesn't just flag problems — it fixes them. The auto-fix engine splits long segments, extends display durations, rebalances line lengths, and retimes subtitles to meet your CPS target. Run it once and re-check. Most projects reach 100% compliance in seconds.
Standards covered
WCAG 2.2 Level AA
Success Criteria 1.2.2 (Captions — Prerecorded) and 1.2.4 (Captions — Live). The global web accessibility standard.
ADA Title II (US)
State and local government entities must provide accessible video content. ADA Title II digital accessibility compliance deadline: June 2026.
European Accessibility Act
Requires accessible digital products and services across EU member states. Enforcement began June 2025.
FCC Closed Captioning Rules
Accuracy, synchronicity, completeness, and placement requirements for broadcast and online video content in the United States.
Who needs accessible captions?
🎓 Universities
ADA Title II and Section 508 require accessible video for publicly funded institutions.
🏛️ Government
State and local government entities must meet WCAG 2.2 AA by June 2026 under updated ADA rules.
🏥 Healthcare
Patient-facing video content requires captions for HIPAA communication accessibility.
💼 Enterprise
The European Accessibility Act affects all digital products sold in the EU from June 2025.
🎬 Content Creators
80% of caption users are not deaf — accessible captions boost engagement, SEO, and audience reach.
📺 Broadcasters
FCC rules mandate captioning quality for all online video content that was previously broadcast.
Frequently asked questions
What is CPS in subtitles?
CPS stands for Characters Per Second — the speed at which a viewer must read a subtitle segment. WCAG 2.2 AA and broadcast standards recommend a maximum of 15–20 CPS to ensure readability. Subtitles exceeding this threshold are difficult for viewers with cognitive disabilities, reading difficulties, or non-native language skills. Vosuba flags segments that exceed your chosen CPS threshold and can auto-fix them by splitting or retiming.
What WCAG standard does Vosuba check against?
Vosuba validates subtitles against WCAG 2.2 Level AA, which covers Success Criteria 1.2.2 (Captions for Prerecorded media) and 1.2.4 (Captions for Live media). It also aligns with FCC closed captioning quality standards and DCMP guidelines for sound description labels.
What is SDH in subtitles?
SDH stands for Subtitles for the Deaf and Hard of Hearing. SDH captions include not only dialogue but also descriptions of non-speech sounds — music, sound effects, environmental audio, and speaker identification. Vosuba's sound detection engine identifies 60+ sound labels and inserts them into your subtitle track following DCMP guidelines.
Do I need WCAG-compliant captions?
If you publish video content for educational institutions (ADA Title II — effective June 2026), regulated industries, European markets (European Accessibility Act — effective June 2025), or government-funded organizations, WCAG 2.2 AA-compliant captions are increasingly a legal requirement. Even outside regulated environments, accessible captions improve SEO, audience reach, and engagement — 80% of captions users are not deaf or hard of hearing.
Make your captions compliant — before you export
Download Vosuba and validate your subtitles against WCAG 2.2 AA. One-click auto-fix. SDH sound labels. Offline on your Mac.