@masterdd15 said:
MP4 files
MP4 files are designed for forward playback. The way the compression works requires the loading of sequential frames. If you will be playing a video in reverse or scrubbing its playback (moving the position input) you want to use HAP. Hap is by far the best format for interactive playback. It is much larger however, so long files will be large. So Mp4 is useful for standard/forward playback of long movies etc.
You should be able to just move the movie files, then reopen the Isadora file (skip relinking the missing media) then see if your files behave as expected.