How to install ffmpeg on Debian 8

is now available for Jessy as a backport: https://packages.debian.org/jessie-backports/ffmpeg

Add something like this to /etc/apt/sources.list (with your preferred mirror):

deb http://ftp.uk.debian.org/debian jessie-backports main

Then

apt-get update
apt-get install ffmpeg

Source: https://superuser.com/a/1082860