If you've been using SimpleScreenRecorder like I have to stream games to Twitch, you know there's some issues that are pretty annoying to solve with it. OpenGL capture requires injecting some memory addresses into the game every launch (very annoying to change these each time with Steam) and while performance is better than using something like ffmpeg with x11 capture, it's still not as good as it could be. Mixing your microphone audio into the stream requires reconfiguring an external mixer (like PulseAudio).
Enter the Open Broadcasting Software Studio rewrite. OBS has been one of the major choices for streaming on Windows for a long time and they've been working on a cross platform rewrite. For me, it's now faster than SimpleScreenRecorder and the only configuration I had to do was select my audio devices in the menu, then add my Twitch.tv stream key. I'm sure there's quite a few bugs left to squash but it's already the best choice for streaming games on Linux.
To get OBS running on Ubuntu 14.04, you need a couple of PPAs.
sudo apt-add-repository ppa:jon-severinsson/ffmpeg sudo apt-add-repository ppa:obsproject/obs-studio
Ubuntu 14.04 uses libav instead of ffmpeg (libav is a fork of ffmpeg). That's lacking some parts of ffmpeg you'll need to run OBS, so the first ppa is upstream ffmpeg builds for Ubuntu. The second ppa is OBS studio itself.
sudo apt-get update sudo apt-get install obs-studio
Will install OBS. You then run it from the command line with
obs. Launch a game, add it to the sources list for your scene. I used the Xcomposite source type.