For Debian package install, first edit the file /etc/apt/sources.list to make sure the added line contains [trusted=yes].

The line for Debian 8 should be:

    deb [trusted=yes] https://cinelerra-gg.org/download/pkgs/debian8 jessie main

The line for Debian 9 should be:

    deb [trusted=yes] https://cinelerra-gg.org/download/pkgs/debian9 stretch main

Next run these commands in a terminal for either one:

    apt install software-properties-common apt-transport-https

Plus for Debian 8 (Jessie), run:

    apt-add-repository https://cinelerra-gg.org/download/pkgs/debian8

Plus for Debian 9 (Stretch), run:

    apt-add-repository https://cinelerra-gg.org/download/pkgs/debian9

Then run these commands to install it:

    apt update
    apt install cin

To update a previous install, run:

    apt update
    apt upgrade cin

To remove Cinelerra-GG run:

    apt remove cin

Debian 9 also has a 32-bit package available.   Use similar instructions as above.