How to fix invalid WebVTT timestamps

Invalid WebVTT timestamps usually mean the file looks close to VTT, but its timing format does not match what browser playback expects.

Quick answer

If your subtitle file came from an SRT source or a messy export, normalize it into clean VTT output with the SRT to VTT Converter.

That fixes the most common timestamp mismatch in one step.

What valid VTT timestamps look like

VTT timestamps use dots, not commas:

00:00:01.000 --> 00:00:03.500

SRT timestamps use commas:

00:00:01,000 --> 00:00:03,500

If a file uses SRT timing inside a VTT workflow, browser players may reject it.

Other common VTT problems

Besides timestamp punctuation, WebVTT files can fail because:

• the WEBVTT header is missing
• formatting was copied from a non-VTT source
• cues were edited manually and structure drifted

If the file began as SRT rather than VTT, How to convert SRT to VTT for HTML5 video is often the cleanest fix instead of hand-editing every cue.

Step-by-step workflow

1. Confirm the destination actually needs VTT.
2. If the source file is SRT, open the SRT to VTT Converter.
3. Paste or upload the subtitle content.
4. Check that the output includes the WEBVTT header and dot-based timestamps.
5. Download the new file and test it in the browser player.

Common mistakes

Renaming the file without converting it

Changing .srt to .vtt does not make it valid WebVTT.

Fixing one timestamp but leaving the rest untouched

If the file came from the wrong source format, normalize the whole file.

Debugging the player before checking the subtitle file

Many playback issues are really subtitle format problems, not player problems.

That is especially true for web player workflows like the one described in How to convert subtitle files for web players.

Related guides

• How to convert SRT to VTT for HTML5 video
• Best subtitle format for HTML5 video
• How to convert subtitle files for web players