Recently I noticed that I was unable to play certain types of audio and video files directly from within Chromium,  I am using Chromium version 10.0.648.133 (77742) on Ubuntu 10.10.  It seems that due to the various licensing issues surrounding the codecs required to playback some of these media types, they are not supported without installing some extra packages.

In order to get MP3 playback support up and running you will need to install the necessary software package using the following command:

 apt-get install chromium-codecs-ffmpeg-extra

After a quick browser restart, you should be able to enjoy MP3 playback on Chromium.

There is a similar process required in order to get MP4 and H.264 playback enabled, however this time you will need to install the following instead:

 apt-get install chromium-codecs-ffmpeg-nonfree

Once again after a quick browser restart, you should be able to enjoy MP4 and H.264 playback on Chromium.