Video was based on an explanations somewhere on my blog, both for replay and for audio (in 6-7: http://blog.lilybiri.com/toggle-shape-buttons). Same for the mute button, where I told the author that there is a bit of a maths mistake in his expression:
Expression cpCmndMute = 1 - cpCmndMute
He reversed it, which will lead to negative 1. Lucky for him that Captivate doesn't understand negative numbers, -1 will be translated to +1. But as an engineer, this feels terribly wrong to me. I don't know why he deleted my comment....
Sorry for ranting...
As for a replay button, in CP5.5 maybe this easier expression could work as well: Assign cpCmndGotoSlide with rdinfoCurrentSlide.
Should check, but for the moment on this system no 5.5 available
