UDP for Digital TV delivery

UDP (User Datagram Protocol) is an essential transport layer protocol in networking, known for its simplicity and speed. It plays a significant role in broadcasting and streaming applications, including digital TV delivery, where data packet loss can be tolerated but speed and delays are crucial.

UDP Multicast Diagram

One of the key applications of UDP is in the delivery of TV content over multicast networks. This approach is commonly used across a range of sectors, with some of the most prevalent use cases as follows:

  • Hospitality Organizations: Hotels, resorts, and other hospitality entities often use UDP multicast to distribute TV content to rooms and common areas
  • Internet Service Providers: Local networks of internet providers leverage this protocol to deliver digital TV services to their subscribers
  • Sports Venues: Stadiums and arenas could use UDP multicast to deliver live feeds of a game or match to various screens throughout the venue

Media Address Format

Media Address configure the destination of the UDP stream. The format for this address is as follows:


In square bracket optional parameters.

  • interface - local interface name, such as eth0. If this field is not defined, the UDP stream will be delivered according to the system routes
  • address - IPv4 address of the multicast group, localhost, or remote host for unicast delivery
  • port - network port for UDP delivery. If not specified, the default port 1234 is used

Additional options can be defined after the # symbol and are separated by the & symbol, similar to the parameters in a typical URL. Here are the available options:

  • socket_size=bytes - defines custom size of the system socket. If not specified, the default value is taken from the system configuration: sysctl net.core.wmem_default
  • sync - enables the transmission of UDP in a separate thread with bitrate syncing
  • no_sync - disable bitrate syncing if it has been enabled globally
  • cbr=Kbps - enables bitrate syncing and turns on the insertion of stuffing packets to achieve a constant bitrate
  • ttl=n - controls the lifetime of the datagram to prevent it from looping indefinitely due to routing errors. The default value is 32
  • sap - turn on SAP. Read more on Session Announcement Protocol for Multicast

Here are some examples of how the media address format can be used in different scenarios with Astra:

  • Multicast delivery on a specific interface: If you want to deliver a UDP stream to a multicast group at the address via a specific network interface like eth0, the address would look like this: udp://[email protected]
  • Multicast delivery on system-defined route: If you want to deliver a UDP stream to a multicast group at the address and you want the system to determine the route (interface), the address would be: udp://
  • Unicast delivery to a specific host: If you're sending a unicast stream to a specific host at the IP address, the address would look like this: udp://
  • Delivery on a specific port: If you want to deliver a UDP stream to a multicast group at the address on a specific port, say 5000, the address would be: udp://
  • Turn on CBR to prepare stream for DVB modulation: If you want to deliver a UDP stream to the DVB modulator, you may needed constant bitrate, say 24000Kbit/s, the address would be: udp://
  • Localhost Delivery with a Specific Port: If you need to deliver a UDP stream to a service on the same server, such as FFMpeg for transcoding, you would use the following address: udp://

Web Interface

To configure a new UDP output using the Web Interface, begin by selecting "New Stream" from the main menu. Then, in the Output List, click on the gear icon and set the "Output Type" to UDP. Alternatively, you can modify an existing stream by opening its settings, adding a New Output, and clicking on the corresponding gear icon.

UDP Output Options

Most options presented in the web interface correspond directly to the components of the UDP address, as described in the "Media Address Format" section.