Perian, which was last updated in 2013, can't be opened because its developer hasn't signed it (which in no way makes it an unacceptable app).
FYI you can call "installer" from terminal to install packages that are untrusted by using the " -allowUntrusted " flag. This seems to bypass gatekeeper entirely.
Or you can go the whole nine yards, i.e. enable installation of apps downloaded from "Anywhere", with (in Sierra, anyhow)
Code:
sudo spctl --master-disable
The new Great Equalizer is the SEND button.
In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire
