dvbcss-protocols

JS sync protocols library for companion synchronisation

dvbcss-protocols is a javascript library implementing client and server protocols for synchronisation between TVs and companion screen applications using the protocols specified by DVB CSS or HbbTV 2.

The library is written in ES5 and works in the browser where it can provide WebSocket based clients only. To use it in applications that will run it the browser, it must be pre-processed using webpack or browserify. It also works in node.js where it provides both UDP and WebSocket clients+servers.

Feature	Supported in node	Supported in browser (webpack/browserify)
CII client (WebSockets)	YES	YES
TS client (WebSockets)	YES	YES
TS client (UDP)	YES
WC client (UDP)	YES
WC client (WebSockets)	YES	YES
WC server (UDP)	YES
WC server (WebSockets)	YES

This library has similarities to the protocol components in pydvbcss and uses some similar patterns.

This project was originally developed as part of the 2-IMMERSE project, co-funded by the European Commission’s Horizon 2020 Research Programme

Getting started

Use in your own project

Install via npm:

$ npm install --save dvbcss-protocols

Or download or clone this repository and build:

$ cd dvbcss-protocols
$ npm install

Browser or node?

If you build your browser application using webpack or browserify then a different entry point will be used that excludes the features not supported within in the browser.

If you use a different build process then you may need to select the entry point manually:

• main_node.js is for node.js and is listed as "main" in package.json.
• main_browser.js is for browsers and is listed as "browser" in package.json.

Run the examples

There are simple examples of clients and servers in the /examples sub-directory. Use the --help option to determine the command line options for each example.

Documentation

JSDoc documentation can be built:

$ grunt doc

Documentation is generated and output as HTML into the doc subfolder.

Unit tests

Unit tests are written using the jasmine unit test framework.

$ grunt test

Simple example

Creating a wall clock client using JSON format messages via a WebSocket connection:

var WebSocket = require('ws');

var clocks = require("dvbcss-clocks");
var Protocols = require("dvbcss-protocols");
var WallClock = Protocols.WallClock;
var createClient = WallClock.createJsonWebSocketClient;

var ws = new WebSocket("ws://127.0.0.1:7681/wall-clock-server");

var root = new clocks.DateNowClock();
var wallClock = new clocks.CorrelatedClock(root);

var client = createClient(ws, wallClock);

Then at some point later, just close the WebSocket connection to stop the client:

ws.close();

There are also functions to create other variants using different serialisations or network connection types; and also for other protocols (CII protocol, TS protocol)...

Factory functions provided

var Protocols = require("dvbcss-protocols");

var CII = Protocols.CII;
var TimelineSynchronisation = Protocols.TimelineSynchronisation;
var WallClock = Protocols.WallClock;

CII protocol (clients only)

• CII.createCIIClient (JSON, WebSockets)

Timeline Synchronisation protocol (clients only)

• TimelineSynchronisation.createTSClient (JSON, WebSockets)

Wall Clock protocol (clients and servers)

• WallClock.createJsonWebSocketClient
• WallClock.createBinaryWebSocketClient
• WallClock.createBinaryUdpClient
• WallClock.createBinaryWebSocketServer
• WallClock.createBinaryUdpServer

Note that only Binary messages via UDP are truly compliant with the DVB-CSS specification. The other variants have been created for convenience for use in other applications that do not communicate directly with a TV implementing DVB-CSS.

Super-quick introduction to the protocols

DVB has defined 3 protocols for communicating between a companion and TV in order to create synchronised second screen / dual screen / companion experiences (choose whatever term you prefer!) that are implemented here:

• CSS-CII - A WebSockets+JSON protocol that conveys state from the TV, such as the ID of the content being shown at the time. It also carries the URLs to connect to the other two protocols.

• CSS-WC - A simple UDP protocol (like NTP but simplified) that establishes a common shared clock (a "wall clock") between the TV and companion, compensating for network delays.

• CSS-TS - Another WebSockets+JSON protocol that communicates timestamps from TV to Companion that describe the current timeline position.

The TV implements servers for all 3 protocols. The Companion implements clients.

There are other protocols defined in the specification (CSS-TE and CSS-MRS) that are not currently implemented by this library.

Licence and Authors

All code and documentation is licensed by the original author and contributors under the Apache License v2.0:

• British Broadcasting Corporation (original author)
• Institut für Rundfunktechnik
• British Telecommunications (BT) PLC

See AUTHORS file for a full list of individuals and organisations that have contributed to this code. .

Contributing

If you wish to contribute to this project, please get in touch with the authors.