Selfhosted

Not like the whole video goes from 1080p to 720p or something but single bits of the drive will fails over time. If that bit is part of your video file, one pixel of one frame will be the wrong color/black. If multiple bits close to each other fail you might get a video stutter. If even more fail your video player will not play the video at all (or just stop playing at the place of the errors).

Yup, bitrot is a thing. Got a few video files from around 2000 only one player can still open and even then there are lots of artifacts. Moving the files periodically helps to reduce risk. Better is to use a file system\software that prevents that. I'm using snapraid on my server now and do regular scrubs.

corrupt files will have glitches in the best case, but more likely have noticeable decoding errors, and completely unplayable files in the worst case (some parts of a video file are essential for processing the rest). that could also happen if the file system metadata gets corrupted, and the OS cannot piece together the file extents or the whole directory anymore.

modern data storage relies on reliable storage medium. to protect yourself against bit rot the only thing you can do is to keep backups on different storage devices. but what does it worth if you don't notice (in time) there's corruption. you need some way to detect it. a catalogue of some sort, like a checksum file for a whole directory tree, automatically extended with new files, ran in checking mode on schedule, and notifeably notifying you about issues. it can be a custom made solution for traditional file systems like ext4, ntfs, xfs, the FATs, etc, or a filesystem that has that function built-in like zfs or btrfs. the latter two don't implement the notification and the schedule part, but they do the majority of the work. also if you want to notice not just corruption but erroneous deletion or modification too, you should also use their snapshot functionality. you can diff them to see if there's any unexpected changes.