okay you followed all the steps on setting mime types either via the htaccess file or via your web hosts control panel( you did ! ) and your video or audio still does not play

Well as it happens some web hosts in trying to save bandwidth, gzip everything by default—including video or audio files!
In Firefox and Opera, seeking will not be possible or the video may not play at all if a video/audio file is gzipped.

If this is occurring , please check your server / hosts and disable the gzipping of Ogg, MP3, M4V and other media files. You can switch off gzipping for video and audio files in your .htaccess file by adding these lines:

# Don't compress already-compressed files

SetEnvIfNoCase Request_URI .(?:gif|jpe?g|png)$ no-gzip dont-vary

SetEnvIfNoCase Request_URI .(?:exe|t?gz|zip|bz2|sit|rar)$ no-gzip dont-vary

SetEnvIfNoCase Request_URI .(?:avi|mov|mp3|mp4|rm|flv|swf|mp?g)$ no-gzip dont-vary

SetEnvIfNoCase Request_URI .pdf$ no-gzip dont-vary

Thanks to Video for Everybody posts and user Bub for pointing this out ;)