Up till recently, I used to watch channel 4 online by installing hal and pepperflash plugin. However, for reasons of which I have no clue, this no longer works on any browser in ubuntu
My solution has been the following:
Install playonlinux
Inside playonlinux, install firefox and accept the automatic installation of flash player and shockwave player. During the installation, it will give you the option of opening firefox. Un-check this option and allow everything to install with firefox not yet opened
When it has finished, you may have to create shortcut to the playonlinux version of firefox
Once done, open the playonlinux version of firefox, Navigate to channel 4. sign in. Voila, it works. It runs in full screen with no tearing (assuming you have compositing enabled).