Install libass9 by entering the following commands in the terminal:
sudo apt update sudo apt install libass9
Description:
library for SSA/ASS subtitles rendering
SubStation Alpha (SSA) is a subtitle file format that allows more advanced subtitles than the conventional SRT and similar formats. . This package contains the shared library for libass.
Homepage: https://github.com/libass/libass
Version: 1:0.14.0-1
Section: universe/libs