Subtitle formats explained
There are more subtitle formats than most people realize. Some are universal, some are niche, and some are legacy formats you will probably never need. This article gives you a plain-English overview of each format and when to use it.
SRT — SubRip
Extension: .srt · Universal format
The most widely supported subtitle format in the world. Plain text with cue numbers and comma-separated timestamps. Works in every video player, every editing tool, YouTube and almost every platform. The default choice when you do not know what the target player needs.
WebVTT
Extension: .vtt · Web standard
The W3C subtitle format for HTML5 video. Supports cue identifiers, styling and positioning. Native support in HTML5 <track> elements. If you are publishing video on the web with native captions, you need WebVTT.
WebVTT reference · SRT to VTT · VTT Validator
ASS — Advanced SubStation Alpha
Extension: .ass · Rich styling
A format used for sophisticated subtitles with fonts, colors, positioning, karaoke effects and drawing instructions. Popular in anime fansubbing and broadcast. Complex to edit by hand. Supported by most desktop players but not by HTML5 <track> directly.
SSA — SubStation Alpha
Extension: .ssa · Legacy of ASS
Predecessor to ASS. Same concept, older syntax. Still found in older anime subtitle releases. Most modern tools treat SSA and ASS as essentially the same format.
SBV — SubViewer
Extension: .sbv · YouTube legacy
A minimal caption format used primarily by YouTube and some broadcasters. Timestamps are written as 0:00:01.000,0:00:04.000. Functional but rarely seen in modern workflows.
SUB — MicroDVD
Extension: .sub · Frame-based
MicroDVD SUB files use frame numbers instead of timestamps: {100}{200}Hello. Timing is relative to frame rate, so the file is only accurate when paired with the correct frame rate. Legacy format rarely used today.
JSON subtitle data
Extension: .json · Programmatic
Not a formal standard — each tool defines its own JSON schema. Typically an array of cues with start, end and text fields. Useful for JavaScript video players, custom subtitle processing and data analysis.
JSON reference · Subtitle to JSON
Choosing the right format
| Use case | Format |
|---|---|
| General distribution | SRT |
| HTML5 video captions | WebVTT |
| YouTube upload | SRT |
| Anime fansub | ASS |
| Programmatic processing | JSON |
| Legacy DVD | SRT or SUB |
What we support
Subtitle Convert handles SRT and WebVTT for conversion, validation and manipulation. Plain text and JSON are also supported for text and data workflows. ASS, SSA, SBV and SUB are documented in the format reference section but not directly convertible — those need specialized software.