What is ASS?
ASS (Advanced SubStation Alpha) is the subtitle format for people who care where the text sits: styles, positioning, fonts, karaoke timing. Anime fansubs made it standard. Converting it to a plain format means the words survive and the choreography does not.
What is LRC?
LRC is the lyrics format music players read for a synced, line-by-line display - a timestamp in brackets, then the line. It has starts but no ends, so a converter has to infer each line's duration from where the next one begins.