It appears that ass to stl conversion seems to represent a transformation of subtitles from Advanced SubStation Alpha subtitles (.ass) to older Win2020 screen subtitle format (.stl). You have to use some dedicated subtitle editor or converter, but the support for .stl subtitles is pretty slim.
Convert Advanced SubStation Alpha subtitles to Win2020 screen subtitle.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert ass to stl on Windows
An online converter for subtitles
Convert from ass file format
|Yes, Subtitle Converter supports ass file conversion as a source file type.||No||No||No||No||No||No||No|
|Yes, Subtitle Converter supports stl file conversion as a target file type.||No||No||No||No||No||No||No|
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.