I had the same need and found this a couple of years ago: code.google.com/p/subeditor/downloads/list Have been using this since then. It seems to take first t

I had the same need and found this a couple of years ago: code.google.com/p/subeditor/downloads/list Have been using this since then. It seems to take first two times to calculate the difference in speed, while third onward it just adjusts the starting point maintaining the same speed.