Introduction to Kurento
What is Kurento?
Kurento Media Server (KMS) is a multimedia server package that can be used to develop advanced video applications for WebRTC platforms. It is an Open Source project, with source code released under the terms of Apache License Version 2.0 and available on GitHub.
The most prominent characteristics of Kurento are these:
Kurento provides building blocks such as WebRTC and RTP senders & receivers, audio/video mixers, media recording, and more. These Media Elements are self-contained objects that hold a specific media capability; they are extremely easy to compose by inserting, activating, or deactivating them at any point in time, even when the media is already flowing.
It is also very easy to extend Kurento and write your own elements, which can then be integrated with the already existing ones!
Application developers use Kurento to control a so-called Media Pipeline with the desired Media Elements, effectively forming a fully customized architecture that is tailored to their needs. Several built-in modules are provided for group communications, transcoding of media formats, and routing of audiovisual flows.
Given the flexible modular approach that Kurento offers, it is possible to achieve both Selective Forwarding Unit (SFU) and Multipoint Conferencing Unit (MCU) application architectures.
Kurento exposes a rich toolbox of media elements as part of its API:
The WebRtcEndpoint is able to send and receive WebRTC media streams.
The PlayerEndpoint can be used to consume media from RTSP, HTTP, or local sources.
The RecorderEndpoint can store media streams into a local or remote file system.
The FaceOverlayFilter is a simple Computer Vision example that detects people’s faces on the video streams, to add an overlay image on top of them.
Jump straight into the Tutorials to see practical examples of all these elements, used in applications built with kurento.
The picture below shows how to use Kurento in three scenarios:
Using the Kurento Java SDK in a standalone Java EE Application Server. The web browser is a client of this application for things like HTML, and WebRTC signaling, while the application itself is client of KMS (using the Kurento Protocol to control KMS).
Complete examples for the supported SDK technologies are described in Tutorials.
Why a WebRTC media server?
WebRTC is a set of protocols and APIs that provide web browsers and mobile applications with Real-Time Communications (RTC) capabilities over peer-to-peer connections. It was conceived to allow connecting browsers without intermediate helpers or services, but in practice this P2P model falls short when trying to create more complex applications. For this reason, in most cases a central media server is required.
Conceptually, a WebRTC media server is just a multimedia middleware where media traffic passes through when moving from source(s) to destination(s).
Media servers are capable of processing incoming media streams and offer different outcomes, such as:
Group Communications: Distributing among several receivers the media stream that one peer generates, i.e. acting as a Multi-Conference Unit (“MCU”).
Mixing: Transforming several incoming stream into one single composite stream.
Transcoding: On-the-fly adaptation of codecs and formats between incompatible clients.
Recording: Storing in a persistent way the media exchanged among peers.
Why Kurento Media Server?
Kurento Media Server (KMS) can be used in the WebRTC Media Server model, to allow for media transmission, processing, recording, and playback. KMS is built on top of the fantastic GStreamer multimedia library, and provides the following features:
Group communications (both MCU and SFU functionality) supporting media mixing and media routing/dispatching.
Generic support for filters implementing Computer Vision and Augmented Reality algorithms.
Automatic media transcoding between any of the codecs supported by GStreamer, including VP8, H.264, H.263, AMR, OPUS, Speex, G.711, and more.
Kurento Design Principles
Kurento is designed based on the following main principles:
- Distribution of Media and Application Services
Kurento Media Server and applications can be deployed, escalated or distributed among different machines.
A single application can invoke the services of more than one Kurento Media Server. The opposite also applies, that is, a Kurento Media Server can attend the requests of more than one application.
- Suitable for the Cloud
Kurento is suitable to be integrated into cloud environments to act as a PaaS (Platform as a Service) component.
- Media Pipelines
- Application development
Developers do not need to be aware of internal Kurento Media Server complexities: all the applications can deployed in any technology or framework the developer likes, from client to server. From browsers to cloud services.
- End-to-End Communication Capability
Kurento provides end-to-end communication capabilities so developers do not need to deal with the complexity of transporting, encoding/decoding and rendering media on client devices.
- Fully Processable Media Streams
Kurento enables not only interactive interpersonal communications (e.g. Skype-like with conversational call push/reception capabilities), but also human-to-machine (e.g. Video on Demand through real-time streaming) and machine-to-machine (e.g. remote video recording, multisensory data exchange) communications.
- Modular Processing of Media
Modularization achieved through media elements and pipelines allows defining the media processing functionality of an application through a “graph-oriented” language, where the application developer is able to create the desired logic by chaining the appropriate functionalities.
- Auditable Processing
Kurento is able to generate rich and detailed information for QoS monitoring, billing and auditing.
- Seamless IMS integration
Kurento is designed to support seamless integration into the IMS infrastructure of Telephony Carriers.
- Transparent Media Adaptation Layer
Kurento provides a transparent media adaptation layer to make the convergence among different devices having different requirements in terms of screen size, power consumption, transmission rate, etc. possible.