https://github.com/nicolas-meilan/fix-opera-linux-ffmpeg

https://github.com/Ld-Hagen/fix-opera-linux-ffmpeg-widevine/

sudo snap install opera

It is necessary to uninstall the old package manually installed. Replace one with the other. In the case of installation via snap, video support works natively forever, even updating versions. It took me years to figure this out, but another user mentioned this a few weeks ago and so I figured it out.

wget https://sourceforge.net/projects/operao/files/libffmpeg.so
sudo cp libffmpeg.so /usr/lib/x86_64-linux-gnu/opera/libffmpeg.so

Pardus 19.1 GNU/Linux (Turkish dist)
Opera 64.0.3417.54

H.264 support for Opera and openSUSE

-----------------START COMMAND---------------

curl -L -O https://github.com/iteufel/nwjs-ffmpeg-prebuilt/releases/download/0.45.1/0.45.1-linux-x64.zip

unzip 0.45.1-linux-x64.zip

sudo mv libffmpeg.so /usr/lib/x86_64-linux-gnu/libffmpeg_h264.so

sudo mv /usr/lib/x86_64-linux-gnu/opera/libffmpeg.so /usr/lib/x86_64-linux-gnu/opera/libffmpeg.so.orig

sudo ln -s /usr/lib/x86_64-linux-gnu/libffmpeg_h264.so /usr/lib/x86_64-linux-gnu/opera/libffmpeg.so

-------------END----------------

Important 1: always acess https://github.com/iteufel/nwjs-ffmpeg-prebuilt/releases/ in your browser to see the most recent version. Today it is the version 0.45.1 - in the future, you will have to change "0.45.1" in all command to the new version.

Important 2: Save these command in a doc page or something else. Every new Opera browser version you will have to do it again in the terminal. Example: Updating from Opera 67 to 68. Normally when you update from Opera 67 to a new opera 67 version, you will not have to do this command again (sometimes yes). But from 67 to 68. Or 68 to 69 always.
You can acess html5test.com and look for "H.264 support". If you see "yes" next to it. The command is working. If not, you will need to do it again.

Important 3: After doing this command, you will need to close and open again the Opera browser to see everything works.

Important 4: Do the first command, press ENTER. Do the second, press ENTER.... Do not try to copy and paste the 5 commands at the same time. I know that you know that, but I am just saying

This codec is a hell of a lot and the team has been operating for years on end, doing nothing to permanently solve it. You don't even want to develop your own.

In my experience, these codecs are much more worked on by the ArchLinux team that provide this codec update along with Opera updates.

Already the infamous .Deb family Ubuntu, Debian and etc ... the updates of these codecs are never available, with this problem in the videos.

After a lot of research and catching up with these problems in .DEB distributions, I found this command on the Forum MXLinux website that solved this error in 99.9%.

It updates the Vivaldi base codec for Opera.

Anyone who wants to try it, feel free.

Follow the command below:

"Definitive" solution for FFPMEG in the Opera browser:

Source: ( https://mxlinux.org/wiki/applications/opera-tips-and-tricks/ )

sudo -v; curl -L vvld.in/lm64 |tail -c+1075 | sudo tar xJ -C / --wildcards *libffmpeg.so --xform 's,.*/,usr/lib/x86_64-linux-gnu/opera/lib_extra/,'

On Windows and Mac, things are more easy, once those libraries are included in them.

A couple of days ago, I came accross a "genius" w10 user who had the bright idea to install w10 home N version., because some other genius told him that they are lighter and thus better for gaming.
In case you do not know, the N version lacks the windows media player, skype, cortana, mtp support and all sorts of codecs.
Opera could not play h264 videos, just like on linux. And firefox could not plat them as well, for the same reason.
I would say "shame", but I am too happy to say it, because I now know that other browsers do not... cater stupid users or stupid use cases.

https://forums.opera.com/topic/35880/opera-cannot-play-certain-videos-on-latest-version-of-kubuntu-19-10

Opera 67.
chromium-codecs-ffmpeg-extra is already the newest version (79.0.3945.79-0ubuntu0.19.10.2).

Is video ever going to work right in Opera for Linux?

On Linux it's a bit more complicated, but it comes down to 'we use what Chromium uses except we can't give it to you ourselves'.

For me, he should say "we use what ubuntu's chromium uses", because the packages opera lists as suggested dependencies (chromium ffmpeg codecs) only exist on ubuntu and nowhere else.
All other major distros build their chromium packages against those 3 libav* libs for that proper codec support, so yes, ubuntu's way is the "unusual" one, although it is not wrong.
Ubuntu on the other hand has a long history on using "unusual" ways for lots of stuff, and imho, that is the core reason a lot of them have failed or were abandoned in the past (unity, mir, upstart etc), because the "usual" way was proven better in the long term.

Staying ontopic, the libav* libraries are way too common to be ignored. Here, in my spartan debian installation, they are used "only" by mplayer, mpv, deadbeef, kodi, firefox, chromium, brave and ffmpeg. It would be true to say that any qt5 lib I have is used by less apps!

On Windows and Mac, things are more easy, once those libraries are included in them

Why don't you use the same tactics on linux as well? I do not think there is a distro out there which does not package the 3 libav* libraries that other browsers depend on for that precious decoding support

the good side of Linux is something doesn't work and you know how to fix it, fix it

Sorry, but you are wrong on that part with the bold letters. The right word there is "opensource".
But opera is closed source, so you just accept what the devs offer you or use something else if you do not like it.
And please do not get me started on true opensource projects with stubborn devs