SRT vs VTT vs ASS: Which Subtitle Format Should You Use?
If you've worked with subtitles for more than a few minutes, you've probably run into at least three different file extensions: .srt, .vtt and .ass. They all store the same basic thing — text that appears on screen at specific times — but they were built for different eras of video and different needs. Picking the right one (or converting between them) depends on where the subtitles are going, not just what's convenient to export.
SRT: the universal default
SRT (SubRip Subtitle) is the oldest and most widely supported of the three. It's a plain text file with a simple structure: a number, a start and end timestamp, one or more lines of dialogue, and a blank line before the next entry. There's no header, no metadata section, nothing fancy.
That simplicity is exactly why SRT has stuck around for over two decades. Every media player, every video editor, and almost every platform that accepts subtitles at all accepts SRT. If you're not sure what format to use, SRT is almost always a safe default.
Its downside is the same as its strength: SRT has no concept of styling, positioning, or fonts. A line of SRT dialogue is just text — any formatting support (like italics) is limited to a handful of basic HTML-style tags such as <i> and <b>, and even those aren't guaranteed to render everywhere.
WebVTT: built for the browser
WebVTT (Web Video Text Tracks, .vtt) was designed specifically for HTML5 video. It starts with a mandatory "WEBVTT" header line and can include extra blocks — NOTE for comments, STYLE for CSS-like styling rules, and REGION for positioning captions in a specific area of the video.
Structurally it's very close to SRT: timestamps, text, blank lines between entries. The main practical differences are the WEBVTT header, a period instead of a comma as the decimal separator in timestamps (00:00:01.000 instead of 00:00:01,000), and optional cue identifiers instead of mandatory sequence numbers.
If you're adding captions to a <video> element on a website using the <track> tag, WebVTT is the format the browser expects natively — which is why converting SRT to VTT is one of the most common subtitle conversions on the web.
ASS/SSA: built for styling
Advanced SubStation Alpha (.ass) and its predecessor SubStation Alpha (.ssa) exist for a completely different reason: control. Where SRT and VTT are mostly about timing text to appear and disappear, ASS was built to let subtitle authors control fonts, colors, positioning, rotation, and even basic animation.
This is why ASS is the standard in anime fansubbing and karaoke-style subtitles — communities that care a lot about how subtitles look, not just what they say. An ASS file has a proper [Script Info] section, a [V4+ Styles] section defining reusable styles, and an [Events] section with Dialogue lines that reference those styles.
The tradeoff is compatibility. Many players and platforms either don't support ASS at all, or only render the plain text and ignore the styling entirely. If you need your subtitles to work everywhere, you'll often end up converting ASS down to SRT, losing the styling but keeping the dialogue.
So which one should you use?
As a rule of thumb: use SRT for maximum compatibility, use VTT when embedding captions directly in a web page, and use ASS only when you specifically need visual styling and know your target player supports it.
In practice, a lot of subtitle work is less about choosing a format from scratch and more about converting between them — a client sends you an .ass file but your platform needs .srt, or your auto-generated captions are in .vtt but you want a plain .srt to edit in a simpler tool. That's exactly what our converters below are for.