Slow down to a freeze frame

Hi Everyone, 

Im doing a trainging video, and I have some recorded footage that moves along the side of a train. (The person who filmed it didnt stop walking lol)

I need to go from normal playback speed, then slow down to freeze on a certain frame for the dialogue to play. Im hoping this will give a smooth effect, of the video slowing down more and more to the freeze frame. (I know it wont be really smooth in playback due to the frame rate, but id like to try and create this effect anyway.)

I hope this makes sense and thanks for the help!