I sing with a chorus that requires us to memorize all the songs we sing. To do this we have MP3 files of our part and the full mix. We play them over and over again. Frequently we want to practice a particularly tough section.and over. We would want to name the book marks such as "key change", "chorus", "Verse 1", "bridge", "tag". These bookmarks would be saved so that the next time we practice they would display and we could jump right to the bookmark. I'm not looking for free. I'm willing to pay for it.