Hi, at first try different computer if possible. Isn't possible that only videos in lower resolution are ok?
The videos are stored on card or in the phone? If in card, isn't possible that the card is corrupted?
Can you double check the cable you're using for transferring?
Good news is that if the videos are OK in the phone they should be uncorrupted. But make a backup as fast as you can. OneDrive, Google disk, anywhere.
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