Differences with Specs

Nowadays most subtitles are made in Aegisub, which uses libass and xy-vsfilter as renderer, so these two renderers become the de-facto spec of ASS.

It's almost impossible for DOM to render exactly same result in every pixels as VSFilter or libass, ASS.js will provide best efforts to accurate rendering.

Here is some differences:

Feature	VSFilter	libass	ASS.js
\be	✅	✅	❌ same as \blur
\q3	✅	❌ same as \q0	❌ same as \q0
fadeaway{width,height}	✅	❌	✅
\k, \kf, \ko, \kt, \K	✅	✅	🚧

See also Differences between Libass and VSFilters.