So I can totally relate to what you described. I’m not a speech pathologist so it’s hard for me to give you any exact pointers especially everyone’s stutter is specific to them. I think you did the right thing, explaining your stutter in writing. When I try to hide it, start switching words to avoid blocks etc it can become worse. Just take it easy and understand that more than likely the people watching the video interview aren’t going to care if you have a speech disfluency or not. I have talked openly to my bosses about my stutter on numerous occasions and they are totally cool with it.