Understanding Subtitle Formats
When distributing video across websites, course platforms, or video hosting networks, captions can be delivered in two primary forms: hardcoded (burned directly into the video pixels) or closed captions (delivered as an external text file parsed by the media player).
The two most common closed caption file formats used today are SubRip (.srt) and WebVTT (.vtt). While they share a similar foundation, their capabilities and target platforms differ significantly.
What is an SRT File?
SubRip (.srt) is the oldest and most widely supported subtitle format. An SRT file is a plain text file structured into numbered sequential blocks, each containing:
1. A sequential numeric identifier
2. Start and end timestamps formatted as HH:MM:SS,mmm (hours, minutes, seconds, milliseconds separated by a comma)
3. One or more lines of subtitle text
Because of its simplicity, almost every video player, video editing application, and social network supports SRT files out of the box.
What is a WebVTT File?
WebVTT (.vtt), or Web Video Text Tracks, was developed specifically for HTML5 web applications and browsers. It builds on the fundamentals of SRT with several modern enhancements:
Header Requirement
Every WebVTT file must begin with the header WEBVTT on the first line.
Period Millisecond Delimiters
WebVTT timestamps use a period rather than a comma: HH:MM:SS.mmm.
Styling and Positioning Capabilities
WebVTT supports CSS styling tags, text alignment parameters, and horizontal/vertical positioning coordinates directly in the markup.
When to Use Burned-In Captions vs SRT/VTT Files
For short-form platforms like Instagram, TikTok, and YouTube Shorts, burned-in (open) captions are the gold standard. These platforms often fail to render external subtitle files reliably on mobile, and viewers cannot easily enable closed captions while scrolling feeds.
For long-form YouTube videos, corporate websites, and accessible education portals, providing downloadable SRT or VTT files alongside your video gives viewers complete freedom to toggle captions on or off and adjust text size to their preference.