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).

There's a workaround, but VLC Media Player (which I think is signed), which is current, might work instead.

Both apps have been around for a long time and are well-reviewed.

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