I've been using bubbleUPnP for ages in audio and I have also used it to serve photos from a tree of directories and it is great giving good control over timing, sorting and where they are displayed. It is particularly good displaying to a DLNA capable TV screen (aren't they all now?). This may not be the most appropriate way of asking the question, if so, I apologise.
However, I have been trying to work out a way to display on the primary display of the renderer itself, in this case a Raspberry Pi4 with a UHD screen attached via one of the HDMI sockets. Why? The greatest problem with running through my Samsung TV is that it locks up the use of one of the Android tablets/phones while the display is in use. Perhaps this is because the TV is not OpenHome compatible? However I would like to be able to run it from the Pi4 with the display through the Pi4.
The system is the same as I have used for audio in the past on my Pi3+s. minidlna, mpd, upmpdcli, bubbleupnpserver plus Android bubbleupnp on both a Samsung A71 and a Samsung Tablet. I do have problems adjusting volume on the audio, it used to work but for the past couple of years I haven't been able to get it to work. Something wrong with the setup somewhere in the 4 programmes being used but I just haven't been able to get it to work, but that isn't the subject of this query.
I've just upgraded to a Pi4 and decided it would be great to be able to plug a screen into it and watch a series of random photos displayed on the screen and controlled by a phone or tablet but doing it is another issue. Displayed on a DLNA capable TV screen is no issue (other than locking up a phone or tablet in the process). Easy enough to get a photo displayed on a window in linux (using feh) and this allows the display of a directory over time. Nice to be able to stick with a linux terminal. I would like to use the capability of bubbleupnp with it's ability to sort large volumes of photos, in multiple (selected) directories which have been randomised into a series not related to the directory structure. (great ability not often seen elsewhere).
I think it is most likely to be a non-bubbleupnp issue ie more likely to be something around the mpd/upmpdcli interface that is where I will need to work but I wondered if anybody out there had solved the issue previously. Maybe it is just the introduction of another piece of software or hardware acting as the photo renderer, which is why I started looking at feh...
Any ideas, anyone?