Subtitle File Formats and Video Containers
Subtitles enhance accessibility, engagement, and SEO for video content. This article explains common subtitle formats, focuses on SRT and VTT, and covers popular video containers and best practices for embedding subtitles.
TL;DR
- Subtitles enhance accessibility and user engagement.
- Most common formats: SRT (simple, universal) and VTT (web-friendly, stylable).
- Containers store video, audio, and subtitles together. Popular options: MP4, MKV, MOV, WebM.
- Keep subtitles separate for APIs and dynamic localization, or embed when delivering a single packaged file.
Subtitles are more than just words on the screen—they make your content accessible, searchable, and globally friendly. Whether you’re streaming, publishing APIs, or producing professional videos, choosing the right subtitle format is key.
Let’s explore subtitle file formats, the most common video containers, and how they work together.
Common Subtitle File Formats
There’s a wide variety of subtitle formats, ranging from simple text files to complex, timed, stylized formats:
| Format | Notes |
|---|---|
| SRT (SubRip Subtitle) | Most widely supported. Simple text with timestamps. Ideal for APIs, web, and streaming. |
| VTT (WebVTT) | Web-native format. Supports styling, positioning, and HTML-like markup. Perfect for HTML5 players and modern streaming. |
| ASS (Advanced SubStation Alpha) | Supports advanced styling, animations, and positioning. Popular in fan-sub communities and professional subtitling. |
| SSA (SubStation Alpha) | Predecessor to ASS. Styling capabilities, less used today. |
| SUB/IDX | Often used for DVDs. IDX stores timing info, SUB stores text. |
| TTML (Timed Text Markup Language) | XML-based. Used in broadcast and OTT standards, including HLS and DASH. |
| DFXP | Variant of TTML. Used in professional streaming and accessibility workflows. |
| SCC (Scenarist Closed Caption) | Used in broadcast TV for closed captions in North America. |
| SMI/SMIL | Less common, used for early web video subtitling. |
| SBV (YouTube Caption) | YouTube-specific format, simple text and timestamps. |
Among these, SRT and VTT are the most widely supported and easiest to use for modern APIs and web/video streaming.
Focus on SRT and VTT
SRT (SubRip Subtitle)
- File extension:
.srt - Structure: Sequential numbered subtitles with start/end timestamps and plain text.
- Example:
1
00:01:12,000 --> 00:01:15,000
Hello, welcome to our video!-
Pros:
- Simple, widely compatible
- Easy to generate, edit, and automate
- Works with most video players and platforms
-
Cons:
- Limited styling (no font, color, or positioning)
VTT (WebVTT)
- File extension:
.vtt - Structure: Similar to SRT but supports web-specific features and styling.
- Example:
WEBVTT
00:01:12.000 --> 00:01:15.000
Hello, welcome to our video!-
Pros:
- Native to HTML5
<track>elements - Supports positioning, styling, and captions for modern web apps
- Compatible with streaming APIs
- Native to HTML5
-
Cons:
- Slightly more verbose than SRT
Video Containers and Subtitles
A video container is like a box—it stores video, audio, subtitles, and metadata together. Popular containers include:
| Container | Common Uses | Subtitle Support |
|---|---|---|
| MP4 | Streaming, web, APIs | Supports SRT and VTT via metadata or as separate files |
| MKV (Matroska) | High-quality video, local playback | Supports many formats: SRT, ASS, SSA, VTT |
| MOV | Apple devices, professional editing | Can embed SRT, but often external tracks are preferred |
| AVI | Legacy format | Limited subtitle support, usually external SRT |
| WebM | Web-native, VP8/VP9 video | Supports VTT for HTML5 playback |
| MPEG-TS | Broadcast, IPTV | Can carry SCC, TTML, or VTT captions |
Tips for embedding subtitles:
- Use SRT for maximum compatibility across devices and legacy players.
- Use VTT for web-native, HTML5, and modern streaming APIs.
- Keep subtitles as separate files for APIs to allow dynamic loading and localization.
- Match timecode formats with video timestamps (HH:MM:SS or HH:MM:SS.mmm) for precise syncing.
Subtitles may seem like a small detail, but they’re a critical part of modern streaming and API workflows. Choosing the right format and pairing it with the right container ensures your content is accessible, professional, and ready for any device.
If you want, I can also create a single “Video Ecosystem Cheat Sheet” article that combines video codecs, audio codecs, containers, and subtitles in one concise, practical guide. It would make an excellent reference for your developers.
Do you want me to do that next?
Updated about 4 hours ago