Here’s a quick video that highlights how to embed a video uploaded to Moodle into a forum. It was created by Bill Hamlin (@bhamlin or billhamlin08 on Youtube) and highlights usage on the Western Oregon University Moodle [http://online.wou.edu].
In the example Bill is uploading a .MOV file.
Note that for this to work the multimedia filter must be enabled on your site (if you’re running 1.9.x or previous or must be enabled at the course level for those who might be running Moodle 2.0) and the extension of the video you want to embed must be set to “yes”. This is the Multimedia filter configuration page
Administration Block => Modules => Filters => enable Multimedia filters
Then ensure that all extensions for videos/files you may upload to display are set to “yes” by accessing “Multimedia Plugins” which is available once the Multimedia Filter has been enabled (see below).
Bill Hamlin, video creator, also has a good many Moodle videos on his Youtube channel, check them all out at http://www.youtube.com/user/billhamlin08.