to replace the libffmpeg..so in the opera (82.0......) directory manually does not work anymore... 
it's getting annoying
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this working for me (Linux Mint):
1
install CHROMIUM
2
open terminal and type in:
sudo mkdir /usr/lib/x86_64-linux-gnu/opera/lib_extra/
and
sudo ln -s /usr/lib/chromium/libffmpeg.so /usr/lib/x86_64-linux-gnu/opera/lib_extra/libffmpeg.so
3
(re)start opera
opera uses chromium's libffmpeg..so
maybe it is necessary to adjust the path
(google translation)