Any way to force download from AFP as opposed to streaming? I have a Yosemite file server that I use to host video files I've taken on my GoPro to various friends and family who want them. Unfortunately, asking "please download them (aka drag them to your machine from the mounted server volume) instead of just double-clicking them (aka opening them in Quicktime directly from the server)" has not stopped people from streaming them and asking why it's very slow to open 720p/1080p video in their choice media players.

Is there any way to prevent this "streaming" using OS X Server and to instead force people to pull down the file to their local file system? If not, what are some other suggestions (the more native, the better) to enforce this?
I would suggest you zip the files and give your friends read-only access to the volume. So when they double click a ZIP file, they will be asked where to extract the file to (as they cannot just extract to your share), which usually by default is their home folder or desktop folder.