Install certbot

sudo apt-get install python-certbot

Generate certificate.  Change unifi.yourdomain.com to the domain name you have pointing to your UniFi-Video controller.

sudo certbot certonly -d unifi.yourdomain.com

Certbot will create the files in “/etc/letsencrypt/live/unifi.yourdomain.com/”

Now you should stop the unifi service.

systemctl stop unifi-video

The following two commands create and install the keystore for the UniFi-Video application.  These commands were copied from here.  Thanks scobber!

echo ubiquiti | openssl pkcs12 -export -inkey /etc/letsencrypt/live/unifi.yourdomain.com/privkey.pem -in /etc/letsencrypt/live/unifi.yourdomain.com/cert.pem -name airvision -out /usr/lib/unifi-video/data/keys.p12 -password stdin
echo y | keytool -importkeystore -srckeystore /etc/letsencrypt/live/unifi.yourdomain.com/keys.p12 -srcstoretype pkcs12 -destkeystore /usr/lib/unifi-video/data/keystore -storepass ubiquiti -srcstorepass ubiquiti

Remove or rename the Trusted Store.  If you don’t, the cameras will connect, but will not record.  The controller will rebuild the ufv-truststore when it starts up and the cameras will be able to record.

mv /usr/lib/unifi-video/data/ufv-truststore{,.old}

Start the UniFi-Video service

systemctl start unifi-video

Now you can check it by going to https://unifi.yourdomain.com:8443