I want to update my FFmpeg package on Debian 9. the stretch version is FFmpeg (7:3.2.14-1~deb9u1) so I tried to add this line to /etc/apt/sources.list
deb http://www.deb-multimedia.org stretch main non-free deb-src http://www.deb-multimedia.org stretch main non-free
Then I run these commands
$ sudo apt-get update
$ sudo apt-get install deb-multimedia-keyring
$ sudo apt-get update
$ sudo apt-get install ffmpeg
$ ffmpeg -version
But I got FFmpeg 3.3.9
Can someone help me to upgrade to FFmpeg 4? I feel that I am not very far from the answer.