My older Mac Pro is a dual-Quad-Core with four internal drives most partitioned into four allowing me to work on one project while optimizing/defragmenting another. My new "previously owned" Mac Pro is a 12-Core with a similar disk set up. The OS's are 10.7.x & 10.12.x and both are running iMovie v9.0.9; this is because I like my Macs to act as a Mac and not as an iPhone. I also have some older software that runs well on older machines (Sorenson Pro Codec v9 although I now know I can upgrade to v11 which should run on newer Mac operating systems).
For over ten years I've been archiving my video projects by backing up the contents of "iMovie Event:name" and "iMovie Project:name." This project I have also added digital audio processed by Garage Band and pulled into iMovie. By temporarily renaming the drive to what was on my old computer, I can get the video back -- the audio is still gone.
Back in the day (about ten years ago?), you could click on the yellow triangle and then select the disk drive and folder of current video to establish a new path.
Lately I've read about a (*.localizer? or *.location?) file that might allow path editing. iDVD had a "Get Information" which included the path of the source material.
This video is going to be cool, an hour long interview of a 90-year-old gentlemen who flew 90 missions from an aircraft carrier over Korea. Data has been archived. Current work-around is to finish this project on my older existing Mac. The hour long video takes 6 hours to create a .MOV file and another 3 hours to create the .MP4 (65GB > 28GB > 2.8GB) of good looking video!
My main issue is path update and where Garage Band audio is stored. When I brought it into the Project Library, did it become part of the iMovie file or remain in iTunes or Garage Band?
Many thanks for any help you may be able to contribute. I'll keep plugging away at it too.