add simpmusic

[IceDBorn]

https://github.com/maxrave-dev/SimpMusic

[HyperKiko]

i have a derivation that wraps the appimage, if that would help. but i can't seem to get gstreamer to work properly

[IceDBorn]

@HyperKiko We have the exact same problem, if you manage to figure it out, please inform us! Might be a problem with the Linux build though, running the appimage with appimage-run, results in the same behavior.