There exist some dedicated subtitle editors that are used not only to edit or create new subtitles, but also to convert them between individual subtitle formats. So it shouldn't be hard to find one that can convert SRT subtitles to SSA (SubStation Alpha) format.
Convert SubRip video subtitle format to SubStation Alpha subtitle data.
We have found 6 software records in our database eligible for .srt to .ssa file format conversion.
Articles and other information relating to srt into ssa conversion:
Create subtitles for 3D movies - How to convert 2D subtitles to 3D subtitle file format with 3D Subtitler and Subtitle3d.com tools
Microsoft Windows software - convert srt to ssa on Windows
Subtitle Workshop is a free application for creating, editing, and converting text-based subtitle files.
Convert from srt file
to ssa file
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned srt to ssa. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
Subtitle 3D is online service that allows users to Convert to Side-by-Side or Top-and-Bottom 3D format. Customize font's size, outline and even 3D depth for the downloaded 3D subtitle. Use multiple output formats for your 3D subtitle: Substation Alpha (.ssa) Advanced Substation Alpha (.ass) VobSub (.idx/.sub pair)
Apple macOS / Mac OS X software - convert srt to ssa on OS X
Jubler subtitle editor is a software program with which users can easily create and edit text subtitles for movies.
Multiplatform software - convert srt to ssa on any platform
Aegisub is a free, cross-platform open source tool for creating and modifying subtitles.
Subtitle Workshop is easy to use freeware subtitle editing tool. It supports variety subtitle formats, which is able to create, edit, and covert. It includes spell check function and an advanced video preview feature to reduce subtitle editing time.
On-line services software - convert srt to ssa on web
Subtitle Converter is a web application used to convert video subtitles.