I have developed this tool at Aquiris Game Studio using Adobe Flash and Action Script 3. The tool was used to create content for a game similar to Guitar Hero, using Brazilian music which Aquiris was developing for Rede Globo. Seeing that we had a lot of content to put inside the game, and the studio decided to outsource this work, a tool such the Track Editor was really necessary, and very helpful.
After loading the mp3 file, the user could start creating notes for a specific music instrument, being able to copy and paste the notes selection, move points from one track to another. The user could also use the snap option that is based on the BPM (Beats Per Minute) set for the music, indentify overlapping notes, zoom in and out and at any moment of the editing process play the song directly from the editor to see if everything is OK. The user was able to save and open the project file at any time to correct anything that he needs. The file saved is based in the XML standard, and the same file is used inside the game engine to show the music notes to the player.