I have a project that has captions throughout - created using text to speech, then corrected - and I discovered that I need to insert some more content in the middle of the video. I need to insert a new caption for the new content and move everything after it down. I cannot find how to do this. Is it possible? It will be an awful lot of work to split and merge my way to the end of the timeline. I might as well just delete the existing captions and start over. What am I missing?