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Advanced Sub Station Alpha (ASSA) Format Reference

Advanced Sub Station Alpha (file extension .ass) is a powerful subtitle format that supports extensive text formatting, animations, and effects.

Overview

The Sub Station Alpha (SSA) format was created by programmer Kotus in 1996 for the anime fansubbing community. In 2002, Advanced Sub Station Alpha (ASSA) was released with new features including layers, alpha channel support, and rotation.

Despite being called “Advanced Sub Station Alpha,” the file extension remains .ass (though .assa would be more accurate).

Key Features:

Powerful text formatting and styling
Animation and transformation effects
Multiple layers and styles
Drawing and vector graphics support
Precise positioning and timing
Alpha channel (transparency) support
3D rotation effects
Can be embedded into Matroska (MKV) files
Supported by FFmpeg for burn-in

Pros:

✅ Extremely feature-rich
✅ Excellent support in players and converters
✅ Precise control over appearance and animation
✅ Multiple styles in one file
✅ Karaoke effects support

Cons:

❌ No new specification since v4.00+ (2002)
❌ Limited number of full-featured editors
❌ Poorly chosen file extension
❌ Unintuitive BGR color format and inverted alpha values
❌ More complex than simple formats like SRT

File Structure

An ASS file consists of several sections, each starting with a section header in square brackets:

[Script Info] — Metadata and script settings
[V4+ Styles] — Style definitions
[Events] — Subtitle lines and their properties

Basic Structure

[Script Info]
Title: My Subtitle
ScriptType: v4.00+
...

[V4+ Styles]
Format: Name, Fontname, Fontsize, ...
Style: Default, Arial, 20, ...

[Events]
Format: Layer, Start, End, Style, ...
Dialogue: 0, 0:00:01.00, 0:00:03.00, Default, ...

Timecode Format

ASS uses a different timecode format than SRT:

hours:minutes:seconds.centiseconds

Important notes:

Hours use 1 digit (no zero-padding)
Minutes and seconds use 2 digits (zero-padded)
Centiseconds (hundredths of a second) use 2 digits
Period (.) is used as decimal separator (not comma)

Examples:

00:01.00          (1 second)
01:15.25          (1 minute, 15.25 seconds)
30:45.10          (1 hour, 30 minutes, 45.1 seconds)

[Script Info] Section

This section contains metadata and global settings for the subtitle file.

Common Fields

[Script Info]
; This is an Advanced Sub Station Alpha v4+ script.
Title: My Subtitle File
ScriptType: v4.00+
WrapStyle: 0
PlayResX: 1920
PlayResY: 1080
ScaledBorderAndShadow: yes
Video Aspect Ratio: 0
Video Zoom: 6
Video Position: 0

Important Fields

Field	Description	Default
`Title`	Name of the subtitle file	(none)
`ScriptType`	Format version	`v4.00+`
`PlayResX`	Video width in pixels	`384`
`PlayResY`	Video height in pixels	`288`
`WrapStyle`	Line wrapping style (0-3)	`0`
`ScaledBorderAndShadow`	Scale borders with video	`yes`
`Timer`	Timer speed percentage	`100.0000`

Important: Always set PlayResX and PlayResY to match your video resolution! The default of 384×288 is rarely correct for modern videos.

WrapStyle values:

0 — Smart wrapping, lines evenly balanced
1 — End-of-line wrapping
2 — No word wrapping
3 — Smart wrapping, lower line wider

[V4+ Styles] Section

This section defines the appearance of subtitles.

Format Line

The Format line defines the order and names of style fields:

Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, OutlineColour, BackColour, Bold, Italic, Underline, StrikeOut, ScaleX, ScaleY, Spacing, Angle, BorderStyle, Outline, Shadow, Alignment, MarginL, MarginR, MarginV, Encoding

Style Line

Each style starts with Style: followed by comma-separated values matching the format:

Style: Default,Arial,20,&H00FFFFFF,&H0000FFFF,&H00000000,&H00000000,0,0,0,0,100,100,0,0,1,1,1,2,10,10,10,1

Style Fields Explained

Field	Description	Example Values
Name	Style name	`Default`, `Title`, `Sign`
Fontname	Font family	`Arial`, `Times New Roman`
Fontsize	Font size in points	`20`, `24`, `18`
PrimaryColour	Text color (BGR + Alpha)	`&H00FFFFFF` (white)
SecondaryColour	Secondary/karaoke color	`&H0000FFFF` (yellow)
OutlineColour	Border color	`&H00000000` (black)
BackColour	Shadow color	`&H00000000` (black)
Bold	Bold (0=no, -1=yes)	`0`, `-1`
Italic	Italic (0=no, -1=yes)	`0`, `-1`
Underline	Underline (0=no, -1=yes)	`0`, `-1`
StrikeOut	Strikeout (0=no, -1=yes)	`0`, `-1`
ScaleX	Horizontal scale (%)	`100`, `120`
ScaleY	Vertical scale (%)	`100`, `120`
Spacing	Letter spacing	`0`, `2`
Angle	Z-axis rotation (degrees)	`0`, `45`
BorderStyle	1=outline+shadow, 3=box	`1`, `3`
Outline	Outline width	`1`, `2`, `0`
Shadow	Shadow depth	`1`, `2`, `0`
Alignment	Numpad alignment	`2` (bottom center)
MarginL	Left margin (pixels)	`10`, `20`
MarginR	Right margin (pixels)	`10`, `20`
MarginV	Vertical margin (pixels)	`10`, `20`
Encoding	Font encoding/charset	`1` (default)

Color Format

Colors in ASS are in BGR format (Blue-Green-Red, not RGB!) with alpha:

&H<AA><BB><GG><RR>

Important notes:

Order is Blue, Green, Red (BGR), opposite of standard RGB
Alpha values are inverted: 00 = opaque, FF = transparent
Values are hexadecimal (00-FF)

Color examples:

&H00FFFFFF = White (opaque)
&H00000000 = Black (opaque)
&H000000FF = Red (opaque)
&H0000FF00 = Green (opaque)
&H00FF0000 = Blue (opaque)
&H8000FF00 = Green (50% transparent)
&HFF0000FF = Red (fully transparent/invisible)

Alignment

Alignment uses numpad-style numbering:

(Top-left)      8 (Top-center)      9 (Top-right)
(Middle-left)   5 (Middle-center)   6 (Middle-right)
(Bottom-left)   2 (Bottom-center)   3 (Bottom-right)

Most subtitles use 2 (bottom-center) as default.

[Events] Section

This section contains the actual subtitle lines.

Format Line

Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text

Dialogue Lines

Dialogue: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text

Example:

Dialogue: 0,0:00:01.00,0:00:03.00,Default,,0,0,0,,Hello, World!

Event Fields

Field	Description	Example
Layer	Rendering layer (0=bottom)	`0`, `1`, `2`
Start	Start timecode	`0:00:01.00`
End	End timecode	`0:00:03.00`
Style	Style name	`Default`
Name	Character name (optional)	`John`, `Narrator`
MarginL	Override left margin	`0`, `10`
MarginR	Override right margin	`0`, `10`
MarginV	Override vertical margin	`0`, `10`
Effect	Transition effect (rarely used)	``
Text	Subtitle text with optional tags	`Hello, World!`

Comment Lines

Comments use Comment: instead of Dialogue::

Comment: 0,0:00:01.00,0:00:03.00,Default,,0,0,0,,This line won't appear

Override Tags

Override tags modify the appearance of text inline. They’re enclosed in curly braces {}:

{\b1}Bold text{\b0} normal text
{\i1}Italic text{\i0} normal text
{\c&H0000FF&}Red text

See ASSA Override Tags for comprehensive documentation.

Common Override Tags

Tag	Description	Example
`\b1` / `\b0`	Bold on/off	`{\b1}Bold{\b0}`
`\i1` / `\i0`	Italic on/off	`{\i1}Italic{\i0}`
`\u1` / `\u0`	Underline on/off	`{\u1}Underline{\u0}`
`\s1` / `\s0`	Strikeout on/off	`{\s1}Strike{\s0}`
`\c&H<BGR>&`	Text color	`{\c&H0000FF&}Red`
`\fs<size>`	Font size	`{\fs30}Large text`
`\fn<name>`	Font name	`{\fnArial}Arial`
`\pos(x,y)`	Position	`{\pos(640,360)}Center`
`\an<1-9>`	Alignment	`{\an8}Top center`
`\fad(in,out)`	Fade in/out (ms)	`{\fad(500,500)}`
`\t(<tags>)`	Transform animation	`{\t(\frz360)}Rotate`

Line Breaks

\N — Hard line break (always breaks)
\n — Soft line break (breaks if needed)

Example:

Dialogue: 0,0:00:01.00,0:00:03.00,Default,,0,0,0,,Line one\NLine two

Complete Example

[Script Info]
; This is an Advanced Sub Station Alpha v4+ script.
Title: Example Subtitle
ScriptType: v4.00+
PlayResX: 1920
PlayResY: 1080
ScaledBorderAndShadow: Yes

[V4+ Styles]
Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, OutlineColour, BackColour, Bold, Italic, Underline, StrikeOut, ScaleX, ScaleY, Spacing, Angle, BorderStyle, Outline, Shadow, Alignment, MarginL, MarginR, MarginV, Encoding
Style: Default,Arial,20,&H00FFFFFF,&H0000FFFF,&H00000000,&H00000000,0,0,0,0,100,100,0,0,1,1,1,2,10,10,10,1
Style: Title,Arial,30,&H00FFFFFF,&H0000FFFF,&H00000000,&H00000000,-1,0,0,0,100,100,0,0,1,2,0,8,10,10,10,1
Style: Sign,Arial,18,&H00FFFF00,&H0000FFFF,&H00000000,&H00000000,0,0,0,0,100,100,0,0,3,0,0,5,10,10,10,1

[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:01.00,0:00:03.00,Default,,0,0,0,,Normal text.
Dialogue: 0,0:00:03.08,0:00:05.08,Default,,0,0,0,,Two\Nlines.
Dialogue: 0,0:00:05.16,0:00:07.16,Default,,0,0,0,,{\i1}Italic{\i0}
Dialogue: 0,0:00:07.24,0:00:09.24,Default,,0,0,0,,{\b1}Bold{\b0}
Dialogue: 0,0:00:09.32,0:00:11.32,Default,,0,0,0,,{\u1}Underline{\u0}
Dialogue: 0,0:00:11.40,0:00:13.40,Default,,0,0,0,,{\c&H0000FF&}Red
Dialogue: 0,0:00:13.48,0:00:15.48,Default,,0,0,0,,{\an8}Top aligned
Dialogue: 0,0:00:15.56,0:00:17.56,Title,,0,0,0,,Title style text
Dialogue: 1,0:00:10.00,0:00:20.00,Sign,,0,0,0,,{\pos(960,200)}On-screen sign
Comment: 0,0:00:01.00,0:00:02.00,Default,,0,0,0,,This is a comment

Character Encoding

ASS files should be saved as:

UTF-8 without BOM (recommended)
UTF-8 with BOM (acceptable)
UTF-16 (less common)

Best practice: Always use UTF-8 without BOM for best compatibility.

Layers

Layers control the rendering order of subtitles:

Layer 0 — Bottom layer (rendered first)
Layer 1, 2, 3… — Higher layers (rendered on top)

Higher layer numbers appear on top of lower layer numbers. Useful for signs that should appear behind dialogue or complex typesetting.

Comments in ASS Files

Semicolon comments: Lines starting with ; in [Script Info] section
Comment events: Use Comment: instead of Dialogue: in [Events] section
Inline comments: Can be added in override blocks (not recommended)

Example:

[Script Info]
; This is a comment
Title: My Subtitle

[Events]
Comment: 0,0:00:01.00,0:00:03.00,Default,,0,0,0,,This line is commented out

Best Practices

Set correct resolution: Always set PlayResX and PlayResY to match your video
Use UTF-8 encoding: For international character support
Name styles descriptively: Use clear names like Default, Signs, Narrator
Set ScaledBorderAndShadow: Set to yes for resolution-independent borders
Use layers wisely: Keep dialogue on layer 0, signs on higher layers
Test with target player: ASS rendering varies between players
Avoid excessive tags: Too many override tags can impact performance
Use comments: Document complex styling or timing decisions

Common Issues and Solutions

Issue: Colors are wrong

Problem: Using RGB instead of BGR format

Wrong: &H00FF0000 (expecting red, but getting blue)
Right: &H000000FF (red in BGR format)

Issue: Text is invisible

Problem: Alpha value set to FF (fully transparent)

Wrong: &HFF0000FF (fully transparent red)
Right: &H000000FF (opaque red)

Issue: Positioning is off

Problem: PlayResX/PlayResY don’t match video resolution

Wrong: PlayResX: 384, PlayResY: 288 (default)
Right: PlayResX: 1920, PlayResY: 1080 (for 1080p video)

Issue: Borders don’t scale

Problem: ScaledBorderAndShadow not set

Solution: Add to [Script Info]:
ScaledBorderAndShadow: yes

Issue: Subtitles overlapping

Problem: Multiple subtitles with same layer and position Solution: Use different layers or stagger timing

Advanced Features

Karaoke Effects

Dialogue: 0,0:00:00.00,0:00:05.00,Default,,0,0,0,,{\k50}Ka{\k50}ra{\k50}o{\k50}ke

Drawing Mode

Dialogue: 0,0:00:01.00,0:00:03.00,Default,,0,0,0,,{\p1}m 0 0 l 100 0 100 100 0 100{\p0}

Complex Animations

Dialogue: 0,0:00:01.00,0:00:05.00,Default,,0,0,0,,{\t(0,4000,\frz360\fscx200\fscy200)}Animated text

See ASSA Override Tags for comprehensive coverage of advanced features.

Renderer Differences

Different players use different rendering engines:

libass — Most common, used by mpv, VLC, MPC-HC
VSFilter / VSFilterMod — Traditional renderer
xy-VSFilter — Enhanced VSFilter with more features
XySubFilter — Advanced renderer with more effects

Note: Some override tags may work differently or not at all depending on the renderer.

Converting to ASS

Subtitle Edit can convert many formats to ASS:

Open your subtitle file
Go to File → Save as…
Select Advanced Sub Station Alpha (*.ass) from format dropdown
Click Save

Tools and Resources

Recommended Tools

Subtitle Edit — Full-featured subtitle editor with ASS support
Aegisub — Advanced subtitle editor, designed for ASS
ASSA Draw — Vector drawing tool (built into Subtitle Edit)
mpv — Video player with excellent libass support

Libraries and Renderers

libass — Portable subtitle renderer
VSFilter — Classic renderer
xy-VSFilter — Enhanced renderer

Documentation

ASS v4.00+ Specification — Official spec (outdated)
Aegisub ASS Tags — Comprehensive tag reference
Matroska Subtitles — Embedding ASS in MKV

Technical Specifications

Property	Value
File Extension	`.ass`
MIME Type	`text/x-ssa`, `application/x-ass`
Character Encoding	UTF-8 (recommended), UTF-16
Line Endings	Windows (CRLF), Unix (LF)
Timecode Format	`H:MM:SS.cc`
Timecode Precision	Centiseconds (hundredths)
Color Format	BGR + inverted alpha
Default Resolution	384×288 (should be overridden!)

Version History

1996 — Sub Station Alpha (SSA) v4 released by Kotus
2002 — Advanced Sub Station Alpha (ASS) v4.00+ released
- Added layers
- Added alpha channel support
- Added rotation and 3D effects
2002-Present — De facto standard maintained by libass and community

Note: The last official specification was v4.00+ in 2002. Modern features are defined by libass implementation and community practice.

Subtitle Edit

Advanced Sub Station Alpha (ASSA) Format Reference

Overview

File Structure

Basic Structure

Timecode Format

[Script Info] Section

Common Fields

Important Fields

[V4+ Styles] Section

Format Line

Style Line

Style Fields Explained

Color Format

Alignment

[Events] Section

Format Line

Dialogue Lines

Event Fields

Comment Lines

Override Tags

Common Override Tags

Line Breaks

Complete Example

Character Encoding

Layers

Comments in ASS Files

Best Practices

Common Issues and Solutions

Issue: Colors are wrong

Issue: Text is invisible

Issue: Positioning is off

Issue: Borders don’t scale

Issue: Subtitles overlapping

Advanced Features

Karaoke Effects

Drawing Mode

Complex Animations

Renderer Differences

Converting to ASS

Tools and Resources

Recommended Tools

Libraries and Renderers

Documentation

Technical Specifications

See Also

Version History