There is one other alternative, it will not give the "accumulating progress bar", but will move pixel by pixel. Also with a couple of labels on the bar, you can show the current slider position, current time into the song, as well as the song length. It also works as a position selector, meaning you can tap anywhere on the bar to jump to that position in the song.
Here is a screen cap of the slider in my skin:
This is the slider code for the above:
Of course you can use any image for the slider / pointer.