Scrolling text box

I’m trying to implement a scrolling text box. Specifically, the text is going to be scrolling at uneven interval. (Song lyrics, like a karaoke machine).

I thought, I could get around this easily enough by building a small algorithm that compares the current line vs the entirety of the text, and scrolls to that percentage. However, using .scroll(percentage) results in the scrollbar always resetting to 0 before actually scrolling, which is unpleasant.

Any suggestions on how to accomplish this?

Thanks!