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.
What is SRT?
SubRip subtitles are about as simple as a file format gets: a number, a start and end time, the lines of text, a blank line, repeat. Nearly every video player and editor on earth reads them.