Supplementary Information

GRIDSHOT®, developed by theFrontDoor, provides SRT output connections from its playout service. Secure Reliable Protocol (SRT) is a point-to-point connection between a server and client. In order to receive a channel, an SRT socket connection must be established (STEP 1) and data transferred (STEP 2).

Step 1: Establish SRT connection

Within the SRT protocol two roles can be distinguished: 

  • Listener:     Waits for incoming connections
  • Caller:         Initiates connection to the listener

1.1 GRIDSHOT® takes on the Listener role and the operator takes on the Caller role. We authenticate the operator by IP whitelisting and with an optional hash in the SRT "streamid" header.

1.2 GRIDSHOT® provides the SRT endpoint listener IP address and port, as well as a stream decryption passphrase (decryption key) by means of which the operator initiates the SRT connection request to our payout server. This will also provide operators with the opportunity to whitelist our IP address in their firewall if required. The operator needs to allow incoming and outgoing UDP packets to our IP address.

1.3 The operator provides its static IP address / range (class C) which is used to initiate the SRT connection. GRIDSHOT® whitelists this as part of the authentication process.

1.4 The operator makes sure that their SRT client software is version 1.4.1 or higher. If not, we need to reject the connection attempt to ensure proper compatibility between the Caller and the Listener.

Step 2: Receiving TV channel stream through SRT

Once the operator is successfully authenticated by GRIDSHOT®, a connection is established. At this phase there are two roles within SRT.

  • Sender:        Server actively sending SRT packets
  • Receiver:     Client application receiving the SRT packets from the Sender

2.1 GRIDSHOT® takes on the Sender role and the operator takes on the Receiver role.

2.2 SRT packet rate control is managed by GRIDSHOT®.

2.3 SRT protocol optimizes reliability, even over unreliable networks. However, factors like latency, jitter and bandwidth which are outside of anyone’s control, may degrade the signal quality.

2.4 As part of improving the SRT connection stability, GRIDSHOT® can conduct latency testing with the operator.

2.5 Please note that if the operator has entered the wrong decryption key provided by GRIDSHOT®, it won’t receive an SRT stream.

Supported by various parties

Our SRT implementation is tested, verified and supported by engineers from multiple companies and their products:

  • Appendix 1: Flussonic (minimum requirement version 21.08)
  • Appendix 2: FFmpeg (minimum requirement version 4.0)

APPENDIX 1: Flussonic

Flussonic version 21.08 and later supports the SRT protocol with encryption. Flussonic settings are based on a configuration file which defines the streams. 

1 Open the configuration file flussonic.conf and add the following lines to establish the SRT connection:

stream [NAME] {
url srt://[PLAYOUT IP]:[PORT] passphrase=[PASSPHRASE];
}

2 Don't forget to reload the Flussonic service.

For more information about stream settings in Flussonic, please visit the Data Source Types page on the Flussonic documentation website.

APPENDIX 2: FFmpeg

FFmpeg version 4.0 and onwards supports the SRT protocol. Because the FFmpeg implementation uses the same SRT library as the GRIDSHOT® playout solution this facilitates interoperability. The following command shows how to set up an SRT connection:

ffmpeg -i 'srt://[PLAYOUT IP]:[PORT]?mode=caller&passphrase=[PASSPHRASE]&transtype=live'

Contact and support

For technical issues and/or questions regarding the SRT setup, please contact theFrontDoor at service@gridshot.net.

Please note that SRT delivery travels over the open internet and is therefore 100% dependent on the availability of the open internet. As the open internet is outside anyone’s control, no guarantees on service levels can be given. For operators requiring a higher reliability, GRIDSHOT® maintains and guarantees an operational service level of 99,99 % for its (fully redundant) GRIDSHOT® playout on location.