If your site contains Quicktime media files, you may want to advise your users of this:
Quicktime media will not play or will play without the player's controls bar if the mime types are not set in the user's browser. This may occur for other media types also (Windows, Real, etc), but I have only verified this problem with Quicktime. Solution:
The USER must edit their Quicktime's browser preferences: In Quicktime, go to Edit > Preferences > Quicktime Preferences > Browser > MIME Settings (located at bottom of Browser tab) > select the mime types that you want Quicktime to play. For best compatibility, I selected Quicktime movie (mov, qt), aac, mpeg-4, 3gpp, 3gpp2, qhtm. Click "OK", then "Apply", then "OK" again. Your users should now be able to play Quicktime media files