
I could imagine that simply most developers may not even think it might be of interest to anyone. However, there may be a reason for not explaining the folder structure.

Either you end up with a big heap of paper containing the manual in almost 40 different languages or you're left behind with a "quick guide" and a note to go online for the full manual, which in many cases is an electronic version of the "quick guide" in 40 languages again. I'm anyhow somewhat annoyed by the policy of many companies regarding their handling of manuals. It could be part of an appendix to the manual for instance. It would be easy to publish a guide describing the folder structure. Someone in the know could surely produce a proper guide in a couple of hours and publish it on line - it's hardly going to break the bank given what the hardware costs! I am surprised that Sony think it is ok to leave it to the likes of you and I as their customers to try to work out the way their file structure operates. Hope this clarifies at least a few points. Otherwise the camera will either indicate that its database is corrupt or still indicate stills/movies which however cannot be displayed because they've been deleted (outside of the camera). Hint: If you're deleting stills/movies by means of a cardreader, after you've transferred them to your PC, you'll need to re-build the camera's database by following this guide. Whatsoever, you should neither delete nor rename any of those folders. However, they may be filled with content once you're using features like the creation of a highlight movie. Some of the folders may be there just for compatibility reasons like PLAYLIST within BDMV. Those XML files carry information which is used by the camera and/or PlayMemories like GPS data (if available), date/time stamp, video resolution, used CODEC and more. Maybe PlayMemories home uses those empty folders to create the destination folders when copying content to harddisk.

On my A6500 camera it's full of empty folders which in number and creation date correspond to the sub-folders within my DCIM folder.
