Step 4 : RUN curl http://www.deb-multimedia.org/pool/main/d/deb-multimedia-keyring/deb-multimedia-keyring_2016.3.7_all.deb -o /tmp/deb-multimedia-keyring_2015.6.1_all.deb && dpkg -i /tmp/deb-multimedia-keyring_2015.6.1_all.deb && rm /tmp/deb-multimedia-keyring_2015.6.1_all.deb && echo "deb http://www.deb-multimedia.org stretch main non-free" >> /etc/apt/sources.list
---> Running in 4f30327e1025
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 4420 100 4420 0 0 775 0 0:00:05 0:00:05 --:--:-- 1058
dpkg-deb: error: '/tmp/deb-multimedia-keyring_2015.6.1_all.deb' is not a debian format archive
dpkg: error processing archive /tmp/deb-multimedia-keyring_2015.6.1_all.deb (--install):
subprocess dpkg-deb --control returned error exit status 2
Errors were encountered while processing:
/tmp/deb-multimedia-keyring_2015.6.1_all.deb
The command '/bin/sh -c curl http://www.deb-multimedia.org/pool/main/d/deb-multimedia-keyring/deb-multimedia-keyring_2016.3.7_all.deb -o /tmp/deb-multimedia-keyring_2015.6.1_all.deb && dpkg -i /tmp/deb-multimedia-keyring_2015.6.1_all.deb && rm /tmp/deb-multimedia-keyring_2015.6.1_all.deb && echo "deb http://www.deb-multimedia.org stretch main non-free" >> /etc/apt/sources.list' returned a non-zero code: 1
This was fixed back in September, if you clone / pull the latest version, this should work perfectly. Closing for now, but if you have any further problems please comment back!
Step 4 : RUN curl http://www.deb-multimedia.org/pool/main/d/deb-multimedia-keyring/deb-multimedia-keyring_2016.3.7_all.deb -o /tmp/deb-multimedia-keyring_2015.6.1_all.deb && dpkg -i /tmp/deb-multimedia-keyring_2015.6.1_all.deb && rm /tmp/deb-multimedia-keyring_2015.6.1_all.deb && echo "deb http://www.deb-multimedia.org stretch main non-free" >> /etc/apt/sources.list ---> Running in 4f30327e1025 % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 100 4420 100 4420 0 0 775 0 0:00:05 0:00:05 --:--:-- 1058 dpkg-deb: error: '/tmp/deb-multimedia-keyring_2015.6.1_all.deb' is not a debian format archive dpkg: error processing archive /tmp/deb-multimedia-keyring_2015.6.1_all.deb (--install): subprocess dpkg-deb --control returned error exit status 2 Errors were encountered while processing: /tmp/deb-multimedia-keyring_2015.6.1_all.deb The command '/bin/sh -c curl http://www.deb-multimedia.org/pool/main/d/deb-multimedia-keyring/deb-multimedia-keyring_2016.3.7_all.deb -o /tmp/deb-multimedia-keyring_2015.6.1_all.deb && dpkg -i /tmp/deb-multimedia-keyring_2015.6.1_all.deb && rm /tmp/deb-multimedia-keyring_2015.6.1_all.deb && echo "deb http://www.deb-multimedia.org stretch main non-free" >> /etc/apt/sources.list' returned a non-zero code: 1