You add captions to your video but viewers still complain they cannot read them. The most common reason is not that the font is too small — it is that the contrast between text colour and background is insufficient. This is an accessibility issue with a well-documented standard to reference.
Note: This article references WCAG 2.2 (Web Content Accessibility Guidelines) as a practical guide. Full WCAG compliance requires more in-depth testing and processes — this article is not a legal compliance claim.
What is contrast ratio and why does it matter?
Contrast ratio measures how different the brightness of text colour and background colour are. WCAG 2.2 recommends:
- Level AA (recommended for most cases): Minimum 4.5:1 contrast ratio for normal text, 3:1 for large text (≥18pt or ≥14pt bold)
- Level AAA (higher standard): 7:1 for normal text, 4.5:1 for large text
White caption on a white background: ratio 1:1 — unreadable. Yellow caption on black background: typically above 10:1 — excellent.
Common caption contrast mistakes
- White text on a light background: When the video scene is outdoors in daylight or features pale colours, white text disappears
- Yellow text on a light background: Often insufficient contrast even if it looks "bold"
- No outline or shadow: Text without a dark border disappears against complex backgrounds
- Caption background too light: Semi-transparent backgrounds are good practice but need to be dark enough
Practical ways to improve caption contrast
You do not need professional tools to start:
- Use a solid dark background: A dark semi-transparent background (rgba 0,0,0,0.7 or more) with white text typically achieves a good ratio
- Add text shadow or outline: A black shadow on white text keeps it readable over any background
- Check with a free tool: WebAIM Contrast Checker (webaim.org/resources/contrastchecker) lets you enter HEX colours and check the ratio — free, no sign-up needed
- Test on real devices: A phone screen outdoors, a small screen — contrast that looks fine on a monitor may not hold up on a phone in bright sunlight
Applying this in common editing tools
- CapCut: Choose text and background caption colours, test contrast before exporting
- Premiere Pro / DaVinci Resolve: Use the safe title area and colour picker to check caption colours
- YouTube auto-captions: Viewers can adjust caption colours in YouTube settings — but your source captions still need sufficient contrast as a starting point
Download accessibility design reference videos via Klypio YouTube downloader or @KlypioBot.
Also see: create Vietnamese subtitles for free, subtitle line break optimiser.