If you use WordPress and have found out that for some reason it is not automatically recognizing certain file extensions as enclosures (my personal experience was that it did not recognize .wmv files) it’s because your server doesn’t have the proper MIME-TYPE setting for that file extension.
The way WordPress automatically creates enclosures is that is queries the server with the URI of your linked file (e.g. an mp3 file) and then parses the server’s returned MIME-TYPE. If it discovers the MIME-TYPE is of either audio or video, it then creates the appropriate enclosure entry.
So, if you ain’t gettin’ your RSS enclosure automatically created, it’s because the MIME-TYPE is missing from the server. But how do you fix that? Every server is different so the fix below only applies to an Apache server with the .htaccess feature enabled.
Here’s the fix:
Just edit the .htaccess file on the local home directory of the Web server that is hosting the audio/video files and add the proper MIME-TYPE that corresponds to the file you’re trying to access. In my case I was adding a MIME-TYPE for WMV (Windows Media Video) files. I added the following line into my .htaccess file:
AddType video/x-ms-wmv .wmv
Here’s a table of other mimetypes. You can also of course Google around and find more.
CAUTION: you need to be careful/aware if you already have an .htaccess file and if so, make sure you edit that file and ADD the above line instead of OVERWRITING that file. Of course if you’re sure that file doesn’t exist then you should be able to create it.