A Beginner's Guide to Subtitle Files: Everything You Need to Know
Subtitle files seem simple once you understand them, but the first time you open one, the structure isn't always obvious. This guide covers the basics: what a subtitle file actually contains, why there are so many formats, and the handful of concepts that make everything else make sense.
What a subtitle file actually is
At its core, a subtitle file is just a list of three things, repeated over and over: a start time, an end time, and a piece of text to display between those two moments. That's it. Everything else — the format, the metadata, the styling options — is built on top of that basic idea.
This is why subtitle files are small (usually just a few dozen to a few hundred kilobytes, even for a full movie) and why they're plain text rather than some complex binary format: the actual information they hold is fundamentally simple.
Why subtitles are a separate file from the video
Keeping subtitles separate from the video file has real advantages. The same video can have subtitle files in a dozen languages without duplicating the (much larger) video itself. Subtitles can be corrected, translated, or restyled without touching the video at all. And viewers can turn them on or off, or choose between multiple subtitle tracks, which wouldn't be possible if the text were permanently rendered into the video frames (that's called "hardcoding" or "burning in" subtitles, and it's generally avoided unless necessary).
The most common formats, briefly
SRT is the oldest and most compatible — plain numbered blocks of timestamp and text. WebVTT is SRT's web-native cousin, built for HTML5 video. ASS and SSA add styling, positioning and basic effects on top of the same timing concept, popular in fansubbing communities. There are others (SBV, TTML, DFXP and more), but SRT, VTT and ASS/SSA cover the vast majority of what you'll encounter.
- SRT — best general compatibility, no styling
- VTT — native to web browsers and HTML5 video
- ASS/SSA — supports fonts, colors, positioning and effects
Where subtitle files come from
Subtitles usually come from one of a few sources: manually written by a translator or captioner, auto-generated by a platform like YouTube's automatic captions, exported from professional captioning software, or extracted from a video that already had embedded subtitle tracks.
Auto-generated subtitles in particular are often a little messy — awkward line breaks, occasional misheard words, timing that's close but not quite right — which is one of the most common reasons people end up converting, cleaning, or re-processing a subtitle file before using it.
Working with subtitle files without installing anything
Because subtitle files are plain text, you genuinely don't need specialized desktop software for a lot of common tasks: converting between formats, stripping out timestamps to get a clean transcript, or exporting to a spreadsheet-friendly format to review timing. That's the whole premise behind this site — these are everyday, low-stakes tasks that shouldn't require downloading and learning a full subtitle editing application.