"Invoke" and not "Toggle" because a slideshow/movie can already be halted via PageUp - which is the key that the user would press several times 99% of the time anyhow - once the slideshow/movie is stopped.
Corrolory would be a .INI setting that determines which of the slideshow/movie options would be invoked by default.
I find slideshow/movie extremely useful when reviewing high-volume alerts from IP cameras. I just kick it off at 50 fps and hit PageUp when I see somelthing interesting....and then use PageUp to back up to the relevant alert.
But having to RightClick | Select Play folder as slideshow/movie | Select 50 fps each time I need to resume the slideshow/movie slows down the review process significantly.
Being able to just press a key to resume the slideshow/movie would speed things up a lot.
Use the following keys:
1..9: Slide show with 1 to 9 seconds delay
Ctrl+1...9: Movie with 1/x seconds delay
Ctrl+Shift+1...9: Movie with 1/100x seconds delay
Thus for 1/50 seconds, use Ctrl+Shift+2.
Next version will have Alt+R to resume slide-show with the FPS used before.