What it is

libass is a portable subtitle renderer for the ASS/SSA (Advanced Substation Alpha/Substation Alpha) subtitle format. It is mostly compatible with VSFilter.

The ASS format can be used for complex subtitle layout. Text can be rendered with borders and shadows in arbitrary colors, with alpha transparency and arbitrarily positioned. Additionally, various vectors transformations (rotations, shearing, scaling) and bitmap operations (box blur, gaussian blur) can be applied. Advanced features include clipping, simple vector drawings and animations.

Known issues and VSFilter differences

Get it

See "Downloads" for the latest release 0.9.8 (released 2009-09-27). For the latest code, check out the Git repository (see "Source").

Confused about other forks/branches?

Libass was originally developed for MPlayer and just recently development split up. MPlayer still uses an in-tree copy of libass.

Related Links

The following projects use libass:

• MPlayer
• VLC
• GStreamer (assrender plugin)
• Aegisub
• XBMC
• avidemux
• PunkGraphicsStream (BD subtitle encoder)

Information about the ASS format:

• ASS specification (incomplete)
• ASS override tags (Aegisub wiki)
• VSFilter source code (guliverkli2)

Other ASS/SSA implementations:

• VSFilter
• asa (defunct)
• Perian