Opera 26 (stable) was released for Linux today and if you've tried it, you might have noticed that, at least on a pretty fresh Ubuntu installation, Flash and H.264 don't work.
So here's how to get Flash and H.264 (used for instance by the YouTube HTML5 player) to work with Opera on Ubuntu. The instructions below should work for all Opera (26 or newer) channels: stable, beta and developer.
How to get Flash working in Opera (Ubuntu)
Opera for Linux supports Pepper Flash, but it's not bundled with it. There are two ways of installing Pepper Flash under Ubuntu (or Linux Mint, etc.) and thus, getting Flash to work in Opera:
A. Install Google Chrome
Pepper Flash comes bundled with Google Chrome so simply downloading and installing Google Chrome will get Flash to work in Opera on Ubuntu:
B. Install pepperflashplugin-nonfree
If you use Ubuntu 14.04, 14.10 and 15.04 (and of course, Linux Mint 17 or 17.1), you can install pepperflashplugin-nonfree, a package that provides Pepper Flash on Ubuntu (and Debian). To install it, use the following command:
sudo apt-get install pepperflashplugin-nonfree
How to enable H.264 in Opera browser under Ubuntu
To enable H.264 in Opera on Linux, you'll need FFmpeg 2.3 or newer. FFmpeg was removed a while back from the official Ubuntu repositories but it has returned with Ubuntu 15.04 Vivid Vervet (currently under development). Update: in Ubuntu 15.04, Opera should support H.264 out of the box.
For Ubuntu 14.04 and 14.10, you can either compile FFmpeg yourself or use A PPA. One such PPA is Kyrill's FFmpeg next PPA, which provides FFmpeg for Ubuntu 14.04 and 14.10, backported from Ubuntu 15.04.
Because this PPA provides FFmpeg packages that don't overwrite Libav, it shouldn't break anything on your system (the new FFmpeg packages ships with renamed libraries, like "libavdevice-ffmpeg", "libavutil-ffmpeg" and so on, so the packages can coexist with Libav from the Ubuntu repositories).
Note: before using this PPA, make sure the "ffmpeg-real" package from Sam Rog's PPA isn't installed, because the two aren't compatible and dpkg will throw an error like: "trying to overwrite [...] which is also in package". So, to remove this package, use the following command:
sudo apt-get remove ffmpeg-real
And another note: Kyrill's FFmpeg next PPA as well as FFmpeg from the Ubuntu 15.04 repositories doesn't provide the -extra packages, so aac encoding is limited to ffmpeg's native encoder, like Doug mentioned in a comment a while back. However, this won't affect Opera.
To add Kyrill's FFmpeg next PPA and install FFmpeg in Ubuntu 14.04 or 14.10 (or Linux Mint 17 or 17.1), use the following commands:
And then simply restart Opera.
sudo add-apt-repository ppa:kirillshkrogalev/ffmpeg-next sudo apt-get update sudo apt-get install ffmpeg
Another PPA which provides FFmpeg (for Ubuntu 14.04 only; this PPA overwrites Libav and I didn't test the consequences of this) is Jon Severinsson's FFmpeg PPA.