Restrict the files mimetypes ?

Issue Summary

I'm using iTunes for a video podcast on 'video' node types. In my videos nodes, I'm attaching two files with filefield :
- a .flv which is for display in the web page (jquery_media to embend it)
- a .mp4 which is for the podcasters and should be enclosed by iTunes

I'd like to have the .flv first, embed it on the web page, use a description like 'Click on the arrow to play' and then the .mp4 as a link to the file with the description : 'Download highres version'.

With jquery_media I can embed only odd or even items, so I have no problem completing my goal BUT the problem is that iTunes takes only the first file for the enclosure.

There are lots of ways I could achieve my goal, some of which are :
- defining two Filefields fields, for instance one for .flv only, the other for everything else (.mp4) (simplest solution, but...)
- use Filefield for .mp4 and File_upload for .flv (or the contrary) (simple solution too, but...)
- leaving .mp4 first and .flv then for iTunes, but then theming the Filefield output for the video type nodes, and making the .flv appear first and then the .mp4 (hack...)

I'm interested in what you think about those solutions, as you know better Drupal than me.

I think a more generic solution to use both .flv and .mp4 in a node, would be usefull to other video podcasts producers, so maybe we could add an option to restrict the files mimetypes for the enclosure. We could use a new variable : itunes_enclosure_mimetypes[$node->type], I can write the code to filter the mimetypes, but Im' wondering what to do for the admin settings :
- add a new column next to "FileField to list in RSS feeds" : "Files mimetypes" with a textfield in which the user should enter a comma-separated mimetypes list (would confuse the UI)
- add a global option for mimetypes enclosure (would apply to all the node types, not good either)
- let the advanced user set the variable himself (hidden feature)