Set a File as default_view of a Folder

I need to set the default view of a Folder to a File (mp3) in the folder.

Plone doesn't offer the File in the Display menue, so I renamed the file to "index_html"

When I rename the File to "index_html" and click/go to the Folder, the file will be downloaded.

Is there a way to simply view the File (as default view of its containing Folder) without downloading it?

index_html is the download view of the file and not easy to change. Neither this will work:

The default view can be also a content item picked from the folder.

Available content item types can be managed from the: Site Setup Control Panel -> Content Rules ( -> Select your new type from the drop down menu -> Click the “Can be used as default page” checkbox.

PS: I think "Content Rules" is a typo, it is "Content Settings"

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