Thanks for replying.
Having looked on various forums found an answer on the apple forums which seems to work for me:
I set up a new share and enabled NFS sharing on the MyCloud Mirror setup. it then gives you a mount point in the format nfs://xxx.xxx.x.xx/nfs/sharename. You can then mount the nfs-share with cmd-k in finder and nfs://xxx.xxx.x.xx/nfs/sharename on the Mac.
I can now create an iMovie library on the MyCloud Mirror and drag and drop files to it from the iMovie library on my MacBook. This lets me archive my videos and ensure they are getting backed up.
Not sure if they way is better or worse than creating a sparse bundle.
“The wokrarround with the sparseimage is one solution, but for me a little bit dangerous. A little damage on the sparsefile and complete content is gone. And using it over network, the risk is even higher. I knew this problem from timemachine sparseimages. So I will be warned.
Maybe using the good old “NFS” is a better solution than afp/smb with sparseimages. You can mount a nfs-share easy with cmd-k in finder and “nfs://servername/share”. (Maybe you have to enable nfs protocol on your NAS and give the host permissions).
Creating or opening an iMovie-Library on this nfs-shares works like charm.
I have try this with OSX10.10.5 and iMovie 10.0.9 and QNAP-NAS.”