SRT vs VTT vs ASS: Complete Subtitle Format Guide

Confused about which subtitle format to use? This comprehensive guide explains the differences between SRT, VTT, and ASS subtitle formats, their compatibility, styling capabilities, and which format is best for your specific use case.

Understanding Subtitle Format Types

Subtitle files come in two fundamental types:

• Text-based formats: Plain text files with timing codes (SRT, VTT, ASS, SUB)
• Image-based formats: Bitmap graphics with timing (SUB/IDX, SUP from Blu-ray)

This guide focuses on the three most popular text-based formats — SRT, VTT, and ASS — which can be easily edited, converted, and styled.

The Three Major Subtitle Formats

SRT (SubRip) Format: The Universal Standard

SRT is the most widely supported subtitle format in the world. Created by the DVD ripping software SubRip, it has become the de facto standard for subtitle distribution.

SRT Structure and Syntax

SRT files are incredibly simple, consisting of four elements per subtitle entry:

1
00:00:12,000 --> 00:00:15,500
This is the first subtitle line.
It can span multiple lines.

2
00:00:16,000 --> 00:00:19,200
This is the second subtitle.

3
00:00:20,000 --> 00:00:23,800
You can use <b>bold</b>, <i>italic</i>, and <u>underline</u>.

SRT Components Explained

• Sequence number: Sequential numbering starting from 1
• Timecodes: Format is HH:MM:SS,MS (hours:minutes:seconds,milliseconds)
• Subtitle text: One or more lines of text
• Blank line: Separates each subtitle entry

SRT Pros and Cons

When to Use SRT

• ✅ Distributing subtitles to a wide audience
• ✅ Uploading to YouTube, Vimeo, or streaming platforms
• ✅ Creating subtitles for movies, TV shows, or documentaries
• ✅ When maximum compatibility is essential
• ✅ Personal media libraries (Plex, Jellyfin, Kodi)
• ✅ Professional video production and distribution

VTT (WebVTT) Format: The Modern Web Standard

WebVTT (Web Video Text Tracks) is the W3C standard for HTML5 video subtitles. Developed as an evolution of SRT, it's designed specifically for web browsers and HTML5 video players.

VTT Structure and Syntax

VTT files are very similar to SRT but with additional features for web integration:

WEBVTT

NOTE This is a comment

00:00:12.000 --> 00:00:15.500
This is the first subtitle.

00:00:16.000 --> 00:00:19.200 align:start position:10%
This subtitle is left-aligned at 10% position.

00:00:20.000 --> 00:00:23.800
You can use <c.yellow>colored text</c> and <b>bold</b>.

VTT Advanced Features

• Cue settings: Control alignment, position, size, and line placement
• CSS styling: Use CSS classes for text styling
• Metadata tracks: Embed chapter markers and descriptions
• Vertical text: Support for vertical writing (Asian languages)
• Voice labels: Identify different speakers with <v Speaker> tags
• Comments: Add NOTE blocks for documentation

VTT Cue Settings Example

WEBVTT

00:00:12.000 --> 00:00:15.500 align:middle line:90%
Centered subtitle at bottom

00:00:16.000 --> 00:00:19.200 align:start position:10% line:10%
Top-left subtitle

00:00:20.000 --> 00:00:23.800 size:50% align:middle
Subtitle at 50% width, centered

VTT Pros and Cons

When to Use VTT

• ✅ HTML5 video players on websites
• ✅ Web-based video platforms (Vimeo, Wistia)
• ✅ When you need precise positioning control
• ✅ Educational videos with chapter markers
• ✅ Accessibility features (audio descriptions, captions)
• ✅ Modern web applications and video streaming

ASS (Advanced SubStation Alpha) Format: The Styling Powerhouse

ASS format is the most advanced text-based subtitle format, offering pixel-perfect positioning, extensive styling, animations, and effects. It's the standard choice for anime fansubbing and projects requiring complex subtitle designs.

ASS Structure and Syntax

ASS files are more complex, with a header section defining styles and an events section containing timed subtitles:

[Script Info]
Title: Sample ASS File
ScriptType: v4.00+

[V4+ Styles]
Format: Name, Fontname, Fontsize, PrimaryColour, Bold, Italic
Style: Default,Arial,20,&H00FFFFFF,0,0

[Events]
Format: Layer, Start, End, Style, Text
Dialogue: 0,0:00:12.00,0:00:15.50,Default,This is the first subtitle.
Dialogue: 0,0:00:16.00,0:00:19.20,Default,{\pos(100,50)}Top-left positioned text.
Dialogue: 0,0:00:20.00,0:00:23.80,Default,{\c&HFF0000&}Blue colored text.

ASS Advanced Capabilities

• Per-character styling: Different colors, fonts, sizes within one subtitle
• Pixel-perfect positioning: Place text anywhere on screen with \pos(x,y)
• Rotation and transformation: Rotate text in 3D space
• Karaoke effects: Animated text coloring synchronized with music
• Fade in/out: Smooth transitions and animations
• Border and shadow control: Outline thickness, shadow depth, blur
• Multiple layers: Stack subtitles on different layers
• Custom fonts embedded: Include font files with subtitles

ASS Styling Tags Example

Dialogue: 0,0:00:10.00,0:00:15.00,Default,Normal text

Dialogue: 0,0:00:15.00,0:00:20.00,Default,{\b1}Bold text{\b0}

Dialogue: 0,0:00:20.00,0:00:25.00,Default,{\c&H0000FF&}Red text (BGR format)

Dialogue: 0,0:00:25.00,0:00:30.00,Default,{\pos(640,50)}Top center text

Dialogue: 0,0:00:30.00,0:00:35.00,Default,{\fad(500,500)}Fade in and out

Dialogue: 0,0:00:35.00,0:00:40.00,Default,{\k50}Ka{\k50}ra{\k50}o{\k50}ke timing

ASS Pros and Cons

When to Use ASS

• ✅ Anime fansubbing and distribution
• ✅ Karaoke videos and music visualizations
• ✅ Professional subtitle styling projects
• ✅ When advanced positioning is critical (avoiding subtitles over on-screen text)
• ✅ Multi-language typesetting (complex scripts)
• ✅ Creative subtitle design and branding
• ❌ NOT for general distribution or streaming platforms