True that you can loose a part of the file or the whole file if a sector is been damaged due to a shock. But it not any happens during writing, it can also happen while reading files. During writing it can do more damage indeed as you state. The reason behind it is because not only the Video file itself is been written, but also the FAT table is updated constantly while writing.
The FAT file contains the location of each file (and each fragmented part of a file) on the hard drive. When this file gets damaged during operation, the OS does not find any of the file locations anymore. Causing all files, or parts on the drive to be unreadable.
Fortunately the FAT file is been written twice on the drive. So with software tools, one can recover data. Engineers can also rebuild the FAT file for very sensitive data piece by piece. The less de-fragmentation of your files, the less work to recover each file.
Like any hard drive one should run tests regularly for bad sectors. So that the bad sectors can be marked for a next writing of files. It doesn't mean the whole drive becomes bad at once.