Hello Linux Geeksters. As you may you Firefox has support for the H.264 format but unfortunately, the gstreamer0.10-ffmpeg package is not available by default on Ubuntu 14.04 Trusty Tahr, so H.264 videos are not natively supported.
So, for watching H.264 videos you will have to install FFmpeg plugin for GStreamer. To my mind, the easiest way to do this is to download the deb package and install it via the command-line interface. I prefer to use gdebi over dpkg because it also installs the dependency packages, if they are available.
Follow the instructions for your system’s architecture exactly, in order to get a successful installation.
How to install the FFmpeg plugin for GStreamer on 32 bit systems:
$ sudo add-apt-repository "deb http://archive.ubuntu.com/ubuntu precise universe"
$ sudo apt-get update
$ sudo apt-get install gdebi
$ wget archive.ubuntu.com/ubuntu/pool/universe/g/gstreamer0.10-ffmpeg/gstreamer0.10-ffmpeg_0.10.13-5_i386.deb
$ sudo gdebi gstreamer0.10-ffmpeg_0.10.13-5_i386.deb
$ sudo sed -i '/precise/d' /etc/apt/sources.list
How to install the FFmpeg plugin for GStreamer on 64 bit systems:
$ sudo add-apt-repository "deb http://archive.ubuntu.com/ubuntu precise universe"
$ sudo apt-get update
$ sudo apt-get install gdebi
$ wget archive.ubuntu.com/ubuntu/pool/universe/g/gstreamer0.10-ffmpeg/gstreamer0.10-ffmpeg_0.10.13-5_amd64.deb
$ sudo gdebi gstreamer0.10-ffmpeg_0.10.13-5_amd64.deb
$ sudo sed -i '/precise/d' /etc/apt/sources.list