What is VTT Format?

Introduction to WebVTT Files

WebVTT (Web Video Text Tracks) is a modern subtitle format designed specifically for web content. It's the standard format for HTML5 video subtitles and captions, offering more features than traditional subtitle formats like SRT. WebVTT is part of the HTML5 specification and is supported by all modern web browsers.

VTT File Structure

A VTT file consists of several components:

  • A WEBVTT header (required)
  • Optional metadata blocks (NOTE, STYLE)
  • Subtitle entries with timing and text
  • Blank lines to separate entries

Important: Unlike SRT format, VTT does not use sequence numbers. Timestamps come directly after the WEBVTT header or metadata blocks.

Example VTT File

Here's a basic example of a VTT file structure:

WEBVTT

00:00:01.000 --> 00:00:04.000
Hello, welcome to OrcaSubtitle!

00:00:04.500 --> 00:00:08.000
Today we'll learn about the VTT format.

00:00:08.500 --> 00:00:12.000
<i>This text will appear in italics</i>

Timing Format

The timing format in VTT files follows this structure:

hours:minutes:seconds.milliseconds --> hours:minutes:seconds.milliseconds

For example: 00:02:15.500 --> 00:02:18.750 means:

  • Start time: 2 minutes, 15 seconds, 500 milliseconds
  • End time: 2 minutes, 18 seconds, 750 milliseconds

Note: VTT uses periods (.) for milliseconds, unlike SRT which uses commas (,).

Text Formatting and Styling

VTT files support various formatting options:

  • <b>Bold text</b> - Makes text bold
  • <i>Italic text</i> - Makes text italic
  • <u>Underlined text</u> - Underlines text
  • <c>Colored text</c> - Changes text color
  • <v>Speaker name</v> - Identifies speakers
  • <ruby>Text<rt>Annotation</rt></ruby> - Ruby annotations

Common Issues and Solutions

1. Browser Compatibility

While VTT is the standard for web video, some older browsers might not support all features. Always test your subtitles across different browsers and consider providing fallback formats.

2. Character Encoding

VTT files should be saved with UTF-8 encoding to ensure proper display of special characters and different languages. This is especially important for international content.

3. Styling Limitations

Some video players might not support all VTT styling features. Test your styling in the target environment before deployment and provide fallback styling.

4. Timing Precision

VTT supports millisecond precision, but some players may round to the nearest second. Test timing accuracy in your target environment.

Best Practices

  • Always include the WEBVTT header as the first line
  • Use UTF-8 encoding for proper character support
  • Keep subtitles concise and well-timed (2-3 lines maximum)
  • Test across different browsers and devices
  • Use appropriate styling for better readability
  • Consider using metadata for additional information
  • Provide fallback formats for older browsers if needed