Troubleshooting videos issues in chromium based browsers
Go to http://security.ubuntu.com/ubuntu/pool/universe/c/chromium-browser/
Download the latest 'chromium-codecs-ffmpeg-extra'
( i386 refers to 32bits & amd64 to 64bits version)
cd <directory-where-you-download-.deb>
ar x <.deb-you-just-download> data.tar.xz
tar -xJf data.tar.xz --strip-components=4 ./usr/lib/chromium-browser/libffmpeg.so
Find where the browser folder is; usually :
# Vivaldi
cp libffmpeg.so /opt/vivaldi/lib/
# Opera
cp libffmpeg.so /usr/lib/x86_64-linux-gnu/opera