This post was last updated 11 years 6 months 2 days ago, some of the information contained here may no longer be actual and any referenced software versions may have been updated!

I ran ffmpeg for the first time on my Mac after upgrading to Mountain Lion (OS X 10.8) and got this message “An application has requested access to X11. Would you like to install X11 now?”

With the release of OS X 10.8 Mountain Lion, ported X11 (Unix) Window and Terminal applications are no longer supported in the native Mac operating system, this means that any applications ported to OS X using Mac Homebrew will no longer work after upgrading to Mountain Lion until you install new versions of X11 and XCode.

Here are the steps required to get your ported Homebrew apps including ffmpeg working again under OS X 10.8 Mountain Lion.

REINSTALL XCODE

Goto the App Store and reinstall the latest version of the XCode development software. When the software is installed, run XCode and goto Xcode > Preferences > Downloads and click Install next to the Command Line Tools package to reinstall XCode command line tools.

Let OS X know where XCode is with the following command

sudo xcode-select -switch /Applications/Xcode.app/Contents/Developer

INSTALL X11

Follow the install link on the X11 popup as shown above or goto http://xquartz.macosforge.org/trac/wiki to download the latest version of the XQuartz Project X Windowing System for OS X. “The XQuartz project is an open-source effort to develop a version of the  X.org X Window System that runs on OS X. Together with supporting libraries and applications, it forms the X11.app that Apple has shipped with OS X since version 10.5.”

Open the X11 dmg and run the install package. Restart your Mac and then update the X11 symlink with this command

sudo ln -s /opt/X11 /usr/X11

UPDATE HOMEBREW

From the command line run

brew doctor

to check the status of your home brew installation. And follow any recomendations there. Update your Homebrew software using

brew update

You may need to install the git repository software for the update to run:

brew install git

Your Homebrew apps including ffmpeg should now run on OS X 10.8 Mountain Lion, and you should be able to update and install new software using the brew install command.