Subtitle files come in several distinct formats, each designed for different use cases and platforms. Understanding the differences between them helps you choose the right format for your needs and know when to convert between them.
SRT (SubRip) — The Universal Standard
SRT is the most widely used subtitle format in the world. It stores subtitles as numbered blocks, each containing a start timestamp, an end timestamp, and one or more lines of text. The timestamp format uses commas as the millisecond separator (e.g., 00:01:23,456). SRT files are plain text, easy to edit manually, and compatible with virtually every media player on every platform. If you are not sure which format to use, SRT is almost always a safe choice. Its simplicity is both its strength and its limitation — SRT does not support font styling, colors, or on-screen positioning.
VTT (WebVTT) — The Web Standard
WebVTT was designed specifically for HTML5 video and is the only subtitle format supported natively by web browsers. It uses a period as the millisecond separator (e.g., 00:01:23.456) and requires a WEBVTT header at the start of the file. Beyond those surface differences from SRT, VTT supports cue settings for vertical text, line positioning, and alignment. You can also style VTT captions with CSS. If your subtitles will be displayed in a web browser using the <track> element, VTT is the correct choice. Converting from SRT to VTT is straightforward — the tool adjusts the timestamp format and adds the required header automatically.
ASS (Advanced SubStation Alpha) — The Styling Powerhouse
ASS is the format of choice when you need advanced typographic control. It supports custom fonts, colors, bold and italic text, precise screen positioning, fade effects, karaoke highlighting, and even animation. The format uses a script-style structure with a header section, style definitions, and dialogue events. ASS is extremely popular in the anime fansub community, where translators use it to create typeset signs, styled dialogue, and elaborate karaoke effects. When converting ASS to simpler formats like SRT, the styling metadata is stripped and only the plain text and timestamps are retained. If you need rich visual presentation, ASS is the best option.
SUB (MicroDVD) — Frame-Based Timing
Unlike the other formats which use time-based timestamps, SUB uses frame numbers to mark when subtitles appear and disappear. Each line is enclosed in curly braces with the start and end frame numbers (e.g., {1200}{1350}Hello). This makes SUB particularly useful in workflows where frame-accurate synchronization matters, such as DVD authoring or video encoding pipelines. The conversion between SUB and time-based formats requires a known frame rate — the SoftSubs converter uses the standard 23.976 fps by default. SUB files are compact and simple but are less commonly used with modern streaming and web-based players.
When to Convert Between Formats
The most common conversion is SRT to VTT, needed whenever you want to embed subtitles in a web page using HTML5 video. Converting to ASS is useful when you want to add styling to plain subtitles for use in players like VLC or MPC-HC that support ASS rendering. Converting from ASS to SRT is common when you need a clean, widely compatible file without styling. The SoftSubs converter handles all of these conversions instantly, preserving timestamps and text content while adapting the format structure to match the target specification.