This is what worked for me in Debian 10:

[*]Install chromium-ffmpeg snap:
$ sudo apt update
$ sudo apt install snapd
$ sudo snap install core
$ sudo snap install chromium-ffmpeg

[*]Keep the original libffmpeg.so file in /usr/lib/x86_64-linux-gnu/opera/ and create inside there a directory lib_extra:
$ sudo mkdir /usr/lib/x86_64-linux-gnu/opera/lib_extra

[*]Create a symlink in the lib_extra directory of the snap latest version libffmpeg.so:

$ sudo ln -s /snap/chromium-ffmpeg/current/chromium-ffmpeg-98516/chromium-ffmpeg/libffmpeg.so /usr/lib/x86_64-linux-gnu/opera/lib_extra

Note: the latest version in my case is 98516, make sure to check yours inside directory /snap/chromium-ffmpeg/current/

After these steps Opera browser plays all kinds of videos i've come across.

Thanks to @mr-matt-eastwood and this post that provided the solution steps!

@vladimir-bardakov The second step of your solution (sudo rm /usr/lib/x86_64-linux-gnu/opera/libffmpeg.so) produces an error about shared libraries, at least in recent Opera versions.

This file must remain and as an extra step create a lib_extra directory inside /usr/lib/x86_64-linux-gnu/opera/lib_extra where the symlink must be placed.

You can see my other detailed comment about the workaround in Debian 10. Many thanks for creating this post and part of the solution!

@vladimir-bardakov The second step of your solution (sudo rm /usr/lib/x86_64-linux-gnu/opera/libffmpeg.so) produces an error about shared libraries, at least in recent Opera versions.

This file must remain and as an extra step create a lib_extra directory inside /usr/lib/x86_64-linux-gnu/opera/lib_extra where the symlink must be placed.

You can see my other detailed comment about the workaround in Debian 10. Many thanks for creating this post and part of the solution!

This is what worked for me in Debian 10:

[*]Install chromium-ffmpeg snap:
$ sudo apt update
$ sudo apt install snapd
$ sudo snap install core
$ sudo snap install chromium-ffmpeg

[*]Keep the original libffmpeg.so file in /usr/lib/x86_64-linux-gnu/opera/ and create inside there a directory lib_extra:
$ sudo mkdir /usr/lib/x86_64-linux-gnu/opera/lib_extra

[*]Create a symlink in the lib_extra directory of the snap latest version libffmpeg.so:

$ sudo ln -s /snap/chromium-ffmpeg/current/chromium-ffmpeg-98516/chromium-ffmpeg/libffmpeg.so /usr/lib/x86_64-linux-gnu/opera/lib_extra

Note: the latest version in my case is 98516, make sure to check yours inside directory /snap/chromium-ffmpeg/current/

After these steps Opera browser plays all kinds of videos i've come across.

Thanks to @mr-matt-eastwood and this post that provided the solution steps!