Hi Nick.
Just played around with the video mode on my Canon 100D. Yes! This is the answer for totality. Allows me to adjust the exposure from the touch sensitive screen and look at the eclipse via the mark 1 eyeball.
So my routine will be to image the partial phase as a series of timed still shots in raw mode. Just before totality take off the filter and switch to switch to video mode at 1 minute before totality, adjusting exposure on the touch sensitive screen of the Canon. I will ensure that the video is at its highest setting and it is shooting in raw mode.
Hope this works out.
Thanks again.
Tom