When you load some .avi file (or any else, by that matter), you have that clip in the bin window by the name, say, xxx. xxx is saved in the folder movie_1.
IF you remove that clip from that folder it was into some other folder (movie_2), the .avi file in the bin window, and in the timeline, becomes useless and is greyed out.
To get it back, the simpliest way is to double-click that greyed file in the bin window and manualy find the location and the moved/removed file, (in this case it's movie_2 and xxx file). Then you click at xxx and it's back.
Not sure about your question ... if your AVI is indeed corrupted internally, I don't think there are any tools to restore it - other than to restore it from a proper backup. Or you have to recreate the AVI from the original source.
TingSern
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Edius 9.4 Pro, Lenovo P72 workstation laptop, 64GB RAM, Xeon CPU, Windows 10 Pro (64 bits), 2 x 2TB Samsung M2.NVME and 1 x 4TB Samsung SSD internal. Panasonic UX180 camera, Blackmagic 4K Pocket Cinema, Blackmagic Pocket Cinema
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