Video files often cause hash mismatches #39
Description
Occasionally, downloads result in a hash mismatch.
A previous cause of this was a race condition, but that issue has been resolved.
Getting to the bottom of this might enable us to avoid redundant downloads, especially of larger files - the problem seems to be exclusive to video files (mp4/m4v).
Edit: GIFs might also be affected.
Edit 2: Potentially related to #43