What is SSA?

SubStation Alpha (or Sub Station Alpha), abbreviated SSA, is a subtitle file format created by CS Low (also known as Kotus) that allows for more advanced subtitles than the conventional SRT and similar formats. This format can be rendered with VSFilter in conjunction with a DirectShow-aware video player (on Microsoft Windows), or MPlayer with the SSA/ASS library. It is also the name of the popular, now discontinued tool used to edit subtitles.

Usage

This subtitle format is frequently used in anime fansubs, either to overlay subtitles onto video while it is being encoded (hardsubbing), or to store subtitle data alongside video data in a Matroska (MKV) container (softsubbing). Hardsubbing is irreversible but does not require VSFilter or other special resources for playback. Softsubbing allows the end user to choose whether subtitles will be displayed and makes it possible to include multiple subtitle streams in the same video file. The current version of SSA is v4.00. There are many freeware and open source subtitling applications that support the SSA format.

Related Software:

Macgo Mac Blu-ray Player: Display SSA format on your Mac.
Macgo Windows Blu-ray Player: Display SSA on Windows platforms.
Macgo Free Mac Media Player: Display SSA for Mac OS X.

Related Source:

How to add and set Subtitles to a Blu-ray movie?
How to sync audio, video, subtitle by Mac Blu-ray Player?

Further Reading:

See SubStation Alpha on Wikipedia.
"SSA/ASS Subtitles". Matroska.org. CoreCodec, Inc. Retrieved 12 July 2010.
Principal sections in an SSA subtitle.