Serviio

I have different sources (folder) for videos, fotos and music on my nas.
So it would be nice to have multiple souces for one target (for example videos).

Additionally I don't know if it's possible to have any external sources?

Can videos be located in multiple locations? No problem. My videos are spread across 7 different folders on four different hard drives. Just add each location, and check the media type (audio, video, image).

Yes, you can use external sources, such as a USB drive connected to the computer or a shared network folder on another device. With network sources, permissions become more of a problem. On Windows, Serviio runs as a local service user, which does not have network privileges. The simplest way to fix that is to change the user account the service runs under. For Mac or Linux, I can't speak to how that might work, but it is possible.