Here’s one way to install the new VLC 3 (Vetinary) on Debian 9.3 (Stretch).

Note that because I’m pulling the software from the Unstable (Sid) repository this method is not suitable for production machines. It may break dependencies of other packages.

1. Add Sid to /etc/apt/sources.list:

# Sid
deb http://deb.debian.org/debian/ unstable main contrib non-free
deb-src http://deb.debian.org/debian/ unstable main contrib non-free

2. Update the repositories list:

# aptitude update

3. Install VLC:

# aptitude -t unstable install vlc libkf5coreaddons5 libkf5crash5

The second and third packages are necessary because apt would complain about them. I’m sure this breaks some dependencies but hey, VLC 3.

Afterwards it may be a good idea to comment the Sid repos out so you don’t get the rest of Sid if you don’t want to. Alternatively set up pinning.