Media offline

Your timeline holds pointers to files sitting somewhere on a disk. Move a folder, rename a drive, unplug an external disk or open the project on a second machine, and the editor goes looking at a path that no longer exists and paints the gap red. Nothing has actually been lost. The cuts, effects and grades all live in the project file, and reconnecting the clips to their new location brings the picture straight back. Most editors have a relink command that finds the rest once you point it at a single file, provided nobody renamed anything. Avoiding it is boring and effective: one media folder per project, consistent drive names, and no renaming after the edit starts.