DLNA (Digital Living Network Alliance) certifies that media players and servers use a standard set of rules to make sure that they all work together. Media servers and players have to follow these rules to use the DLNA stamp. DLNA breaks down the rules into layers. The layers that most people are interested in are connectivity and media format.
The DLNA Model
- Connectivity: sets the rules that the server or player can connect to home networks. For example DLNA devices must support at least one of 802.11 (WiFi), Ethernet, HomePlugAV and a few others. The DLNA standard does not specify the speed of the connection.
- IP Networking: all DLNA devices communicate with each other using the TCP/IPv4 protocol. This is what home routers use. You should be familiar with IP addresses like 192.168.0.10. These addresses in your home network mean that you are using TCP/IPv4. TCP/IP is carried over Ethernet and WiFi connections.
- Discovery and Control: DLNA devices use the UPnP protocol to find other DLNA devices in your home network. UPnP is a protocol that is carried over TCP/IP. If it wasn’t for UPnP your media player would never find the server.
- Media Management: This part of the standard lets devices share information about media libraries, artists, albums,… The standard says that UPnP-AV 1.0 is used to share this information.
- Media Transport: specifies how media is streamed. DLNA uses the same part of TCP/IP as your browser to carry media streams. It uses HTTP Quality of Service.
- Media Formats: This is the part everyone gets hung up on. For a media player/server to be DLNA certified it must support all of the following file formats. The device may support any other format but must support these. When a player does not support the native format of a file, then the server may transcode it to one of the standard formats.
- Link Protection: Digital Rights Management (DRM) to protect commercial content on a home network. The standard used is DTCP-IP.
Supported File Types
Notice that the DLNA standard does not say anything about the media “container”. The container is what you see as the file extension. Common video containers, for example, are .avi, .mkv, .mp4 and .divx. each one of these containers can contain video that encoded using any number of other formats such as H.264 (MPEG4/AVC).
Most DLNA devices support much more than the basic set of formats and most will transcode to supported formats if the player does not support the video or audio codec used. Transcoding can use up a lot of power on your device and can really slow it down. When streaming media, it’s nearly impossible to tell which format the media server and whether it’s being transcoded or not without sophisticated equipent.