Sorry, I donlt think my last change to “local” nfs had taken effect, restarted - cleaned library and now seems much faster - the same 5Gb file now only taking a few second before it starts playing.
In case anyone finds this useful I added the following to /etc/fstab
synology is a host name supported by a local dns server, you can substitute the ip address of you NAS device.
synology:/volume1/video/films /mnt/films nfs noatime,noauto,x-systemd.automount,async,nfsvers=3,rsize=8192,wsize=8192,nolock,nofail,local_lock=all,soft,retrans=2,tcp 0 0
synology:/volume1/video/tv /mnt/tv nfs noatime,noauto,x-systemd.automount,async,nfsvers=3,rsize=8192,wsize=8192,nolock,nofail,local_lock=all,soft,retrans=2,tcp 0
Apologies if any of this is incorrect- its improved things for me but I am no expert - lots of googling today!