did you make the script executable?
(BTW: "didn't work for me" isn't a meaningfull description of what did and didn't happen after you did whatever)
I had made the script executable this is what I get running it. Incidentally it looks like you were running the script as root, I thought it was meant to be as user.
# ./vivaldi-libffmpeg-install-1-1-4.sh
[/code]
ian@sid:~/vivaldi$ sh ./vivaldi-libffmpeg-install.sh
./vivaldi-libffmpeg-install.sh: 33: ./vivaldi-libffmpeg-install.sh: function: not found
vivaldi-ffmpeg-install v.1.1.5 (build 2017-04-11)
Adds libffmpeg.so for Vivaldi installation on system.
I found the alternative script which does work in the same thread on the Vivaldi forum as the one above. It does not work with Opera.
Regarding "didn't work for me" it was just a statement of fact I didn't add any details as I had found an alternative script which did work for me and allow playing of media on Twitter, well in Vivaldi not Opera