Depsite DLNA beeing an open and proven standard for media services in a home network, the Ubuntu Linux situation is far from perfect.
Only a small number of projects, some abandoned. The default media player applications, Rhythmbox for Music, Totem for Videos and Shotwell for Photos, don’t know nothing about DLNA.
The Pulseaudio sound framework has some support for playing audio over a local network, but that doesn’t work out of the box.
Ubuntu as Media Server
This sections covers, how to use a network media player, as your sound card on the desktop. For information on how to share your video and audio and pictures collection on the local network, see External Drives