Does anyone know of an application available to macs that allows me to record my screen activity that can record what something like logic is playing and my voice through a external microphone? I have Jing which is pretty good but it doesn't have two audio inputs and i don't really want to record myself doing stuff in silent and then go back and talk over it.

Gibson Les Paul Classic 1960
Engl Powerball 120 Watt
Orange PPC212 Cabi
ISP Decimator
MXR 10-band EQ
Boss OS-2
Can't you just input the track you sing-along-to into the program which you use to record yourself sing?