What DLNA server are you using? The DLNA server is controlling the presentation of the media. I use Serviio (disclaimer: I wrote the Roku profiles included with Serviio and am a moderator on their forum, but not an employee). Serviio has multiple presentation settings, one being a Folder view. I just checked it, as I have one folder that has video, music and image files. Unfortunately, the media is still separated by content, as the folder appears under all three headers, but it only shows the media that matches the media type content.
You could probably build a playlist that includes all of the media and they could be played from that single playlist. Nope, just tried that and the playlist only shows videos, which is the only category I have playlists enabled for.
So bottom line: It's not RMP that's the issue, it's your DLNA server. Nothing Roku can do about that.
Dan
Roku Community Streaming Expert
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