[coppsilgold]

Then this is either an exploit or more likely the mp4 file is virtual. You can find out if you are so inclined by grabbing it from two separate accounts using two separate devices (or keys) and then compare how many of the segments are identical.

Also, I assume the file in question is 4K content. Don't know about how they treat other types.

[direwolf20]

The normal way to do it would be to deliver different byte ranges per user