SRT, VTT, ASS: Subtitle File Formats Explained

SRT, VTT, ASS, SCC, TTML — the alphabet soup of subtitle formats can be confusing. Here's a clear guide to the most important formats and when to use each one.

SRT (SubRip Text) is the most widely supported subtitle format and the safe default for most use cases. An SRT file is a plain text file with a simple structure: a sequential number, a timecode range in the format HH:MM:SS,mmm --> HH:MM:SS,mmm, and one or more lines of subtitle text. It supports basic text formatting (bold, italic, underline) through HTML-like tags but not advanced styling. SRT files work with virtually every video player, platform, and editing tool. If you're not sure which format to use, SRT is usually the right choice. VTT (WebVTT or Web Video Text Tracks) is the web standard for subtitles, designed specifically for HTML5 video. It has a similar structure to SRT but uses slightly different timecode format (HH:MM:SS.mmm with a period instead of a comma) and supports more advanced styling options through CSS. VTT is the preferred format for YouTube subtitle uploads, web-embedded video players, and any video distributed primarily through browsers. ASS (Advanced SubStation Alpha) and its predecessor SSA support the most sophisticated subtitle styling of any common format — custom fonts, colours, positioning, animations, and karaoke-style effects. It's widely used in anime fansubbing and gaming subtitles where visual style is part of the viewing experience.

Beyond the common consumer formats, broadcast and professional streaming environments use specialised subtitle formats. SCC (Scenarist Closed Captions) is the legacy format used in North American broadcast television for Closed Captions. It encodes caption data in a binary format and was the standard for many years before digital broadcasting. Many broadcast delivery specifications still require SCC for US content. TTML (Timed Text Markup Language) is an XML-based format developed by the W3C that supports advanced styling and is used in professional broadcast and streaming workflows. Netflix, Amazon Prime, and other major streamers typically require TTML or its profiles (EBU-TT, IMSC) for subtitle delivery. IMSC (Internet Media Subtitles and Captions) is a constrained profile of TTML that has become increasingly common for streaming delivery. SRT files submitted to streaming platforms are typically converted internally to IMSC or similar formats. For Digital Cinema Package (DCP) delivery at film festivals and cinemas, SMPTE-TT or CineCanvas XML subtitle formats are used, embedded within the DCP package. These formats support the precise visual control required for theatrical presentation and are generated using specialist DCP authoring tools.

Format selection should be driven by where your video will be distributed, not personal preference. For web distribution via YouTube, SRT and VTT are both fully supported — VTT is technically the native web format but YouTube handles both equally well. For direct website embedding using HTML5 video, use VTT for the best browser compatibility. For video editing software like Premiere Pro or DaVinci Resolve, SRT is universally supported for import and export. For Avid Media Composer and other broadcast editing systems, check your specific version's subtitle import capabilities — different versions have different format support. For Netflix delivery, check the Netflix Partner Help Center for their current specification — requirements change and vary by territory, but TTML profiles are typically required for final delivery. For Vimeo, SRT and VTT are both supported for uploaded caption files. When working with translation agencies or subtitle vendors, SRT is the safest exchange format because every tool in the supply chain supports it. Convert to platform-specific formats as the final step before delivery. Zingo exports in SRT and VTT formats, covering the vast majority of distribution workflows — if you need a specialist broadcast format, most professional subtitle editing tools can convert from SRT as a starting point.