Why subtitles do not show in HTML5 video
TL;DR — Diagnose and fix the most common reasons subtitle tracks fail to render in HTML5 video players, from wrong file formats to missing WEBVTT headers.
If subtitles are not showing in your HTML5 video player, the problem is almost always one of a few fixable causes.
Quick answer
HTML5 video requires WebVTT format. If captions are not rendering, the file is likely in the wrong format, has a missing header, or is not being loaded correctly by the player.
The most common causes
1. Wrong subtitle format
HTML5 <track> elements are designed for WebVTT. Browsers will silently ignore SRT or ASS files in most cases, even if the player loads without an error.
Fix: Convert your subtitle file to VTT using the SRT to VTT Converter or ASS to VTT Converter.
2. Missing WEBVTT header
A valid VTT file must start with the exact string WEBVTT on the first line. A file that looks almost like VTT but lacks this header will fail to parse.
WEBVTT
00:00:01.000 --> 00:00:03.500
Your subtitle text here.Fix: Open the file in a text editor or run it through the converter to confirm the header is present.
3. Comma instead of dot in timestamps
SRT uses commas (00:00:01,000). VTT requires dots (00:00:01.000). A file with comma-based timestamps will not be recognized as valid WebVTT.
Fix: Convert the file properly rather than renaming the extension.
4. Wrong MIME type on the server
Even with a valid VTT file, some servers do not serve .vtt files with the correct MIME type (text/vtt). Browsers may block the track load when the content type is wrong.
Fix: Add the correct MIME type in your server or CDN configuration:
text/vtt vtt5. Cross-origin (CORS) issues
If the video and the subtitle file are on different domains, the browser may block the track due to CORS policy. This is a common issue when hosting static assets on a CDN or separate domain.
Fix: Make sure the server serving the VTT file includes an appropriate Access-Control-Allow-Origin header.
6. File path or URL is wrong
A typo in the <track> element src attribute will load silently with no visible error in most browsers.
Fix: Open the subtitle URL directly in the browser to confirm it loads. A 404 is easy to miss in the player UI.
Diagnostic checklist
Work through these in order before looking for complex causes:
- Is the file in VTT format with a
WEBVTTheader? - Are timestamps using dots, not commas?
- Does the file URL return a 200 response with
content-type: text/vtt? - Are the video and subtitle file on the same origin, or is CORS configured correctly?
- Is the
<track>elementsrcpointing to the right path?
Related guides
Use the SRT to VTT Converter
Convert SubRip subtitle files into WebVTT format for HTML5 video and browser players. No signup, no upload, and everything runs locally in the browser.
Open SRT to VTT