ASS
From Aegisub Wiki
[edit] About
ASS (Advanced SubStation Alpha) is the primary working format used in Aegisub. ASS is an extension of the old SSA format. It is the most advanced subtitle format in widespread use, featuring advanced effects such as transformations and movement. AS5 has been proposed as a successor to it.
ASS is an advanced subtitle which allows multiple lines, optionally with different styling, displayed on screen simultaneously, and also allows for animation.
[edit] Rendering
VSFilter's TextSub is ASS's de-facto reference renderer. However, since it is closely tied to Win32, and is rather inneficient, many replacements have emerged over the years. However, none has ever succeeded in fully implementing the ASS standard.
For a comparison of those renderers, please see this page on the asa Wiki.
