No, deducting a song position from the current scrolling position is too unreliable. Especially with pdf files where you can have repeats, del segnos and what not. Even with plain text, scrolling by 10 pixels could mean no change in position or maybe a jump by 30 seconds. And even with plain text, there are parts of songs with lots of text and parts with no text, so deducting the correct song position is impossible.