Understanding Video Rooms

概要

This guide introduces the concept of Video Room and helps developers decide which type of Room is most appropriate for their use-case:

• WebRTC Go Room
• Peer-to-peer (P2P) Room
• Group Room

This guide also introduces the different alternatives for creating Rooms as well as their advantages and drawbacks:

• Rooms creating using the REST API
• Ad-hoc Rooms

Signaling and Media

RTC (Real-Time Communication) services are typically architected in two layers:

• Signaling Plane: It deals with the control information. The communicating entities typically exchange signaling messages for agreeing on what’s to be communicated (e.g. audio, video, etc) and how’s to be communicated (e.g. codecs, formats, etc.)
• Media Plane: It deals with the media information itself. Media packets typically transport encoded and encrypted audio and video bits.

In Twilio Programmable Video signaling always takes place between clients and the Twilio’s cloud, which orchestrates the communication. Media in turn may be mediated by Twilio but might also be exchanged directly among clients.

Video Rooms

The notion of a Room is central to Twilio Programmable Video. Intuitively, a Room represents a virtual space where end-users communicate. Technically, a Room is a computing resource that provides Real-time Communications (RTC) services to client applications through a set of APIs. More specifically, a Room provides:

• A session service: so that end-users can connect and disconnect from Rooms. When an end-user connects we say it is a Room Participant.
• An RTC Service: so that Participants can communicate audio, video and data using WebRTC.

Video Rooms are based on a publish/subscribe model. This means that a Participant can publish media Tracks to the Room. The rest of Participants can then subscribe to such Tracks to start receiving the media information.

Twilio Programmable Video exposes four types of Rooms with different capabilities: WebRTC Go Rooms, P2P Rooms (Peer-to-Peer ), Group Rooms, and Small Group Rooms.

Video WebRTC Go Rooms

Go Rooms can be used for one-on-one video calls. Participant minutes are FREE and 25 GB of TURN server usage per month is included. Go Rooms use a peer-to-peer topology and are similar to P2P Rooms, however, the maximum number of participants in a Go Room is 2. There can be a maximum of 100 concurrent participants at a time per account, for example, 50 rooms with 2 participants.

Video P2P Rooms

In a P2P Room Participants exchange media directly so that:

• Media is encrypted end-to-end (E2E) using WebRTC security protocols.
• Twilio does not mediate in the media exchange, which takes place through direct communication among Participants. The only exception is when media exchange requires TURN. In that case, a TURN server will blindly relay the encrypted media bits to guarantee connectivity. The TURN server cannot decrypt or manipulate the media.
• As Twilio does not intercept the media in P2P Rooms, it is not possible to record or to transcode the media or to make it interoperate with other RTC services.
• Despite not being in the media path, Twilio manages the signaling path making it possible for Participants to discover each other and to negotiate the communications in agreement with the application and SDK requirements. Hence, signaling connectivity to Twilio’s cloud is still necessary.

The following picture illustrates the architecture of a P2P Room.

As seen above, in a P2P Room, clients need to send their media streams once per subscriber. As a result, upstream bandwidth (and typically battery consumption) scales as n-1, where n is the number of Participants. Because of this, P2P Rooms do not scale well with n.

Video Group Rooms

In a Group Room, Participants exchange media through Twilio. Group Room:

• Participants publish media to a Twilio Selective Forwarding Unit (SFU). An SFU is a Media Server that decrypts the media, processes, re-encrypts and routes the media tracks to the correct destinations.
• As a result, media is not E2E encrypted as the SFU keeps media unencrypted in memory, to process it.
• As Twilio acts as media middleware, Group Rooms can provide services such as recordings and public switched telephone network (PSTN) interoperability.

The following picture illustrates the architecture of a Group Room

As shown above, in a Group Room clients only need to publish their media tracks once to the SFU, which clones and routes the media to the correct subscribers. Because of this, upstream bandwidth and battery consumption are independent of the number of Participants.

Comparing Room Types

The following table illustrates the main properties of the different Twilio Rooms:

1n denotes the number of Subscribers that, by default, is the same as the number of Participants
2Can support up to 10 audio-only participants, but max 3 participants recommended when video is published

Creating Rooms: REST vs. Ad-hoc

There are two alternatives for creating Rooms: The Rooms REST API and Ad-hoc Rooms

The Rooms REST API

Developers can create Rooms by POSTing an HTTP message to Twilio. The Rooms REST API documentation provide reference information as well as examples on how this can be done for all our Room types. Creating Rooms through the REST API should only be done when the additional flexibilty is needed, otherwise using Ad-hoc Rooms will help your application scale more effectively. For more information on this, see the Guide to Scaling Applications.

Rooms created using the REST API comply with the following:

• First join timeout: the first Participant must join within 5 minutes after Room creation. Otherwise the Room is destroyed.
• Last leave timeout: the Room is destroyed 5 minutes after the last Participant leaves.
• Max Participant duration: a Participant can be connected to the Room up to 4 hours. After that time the Participant is disconnected.
• Max Room duration: a Room may exist up to 24 hours from creation time. After that time the Room is destroyed and all Participants get disconnected.

Ad-hoc Rooms

Rooms can also be created just-in-time when the first Participant connects. When a Room is created that way, we say it is an ad-hoc Room. This is the recommended way of creating rooms since Ad-hoc Rooms allows you to create many Rooms in a short period of time, and they allow you to create a Room without having to make a REST API call. You can scale with the REST API but you will have a limitation around burst creation of Rooms. For more information on this, see the Guide to Scaling Applications. In order to use ad-hoc Rooms, developers must enable "CLIENT-SIDE ROOM CREATION" in the Twilio Console Room Settings following these simple steps:

• Set the STATUS CALLBACK URL to the URL where the status callbacks should be received (can be left empty).
• Set the ROOM TYPE to the type of Room to be created: Go (for WebRTC Go Rooms), Peer-to-peer (for P2P Rooms), or Group (for Group Rooms)
• Set the CLIENT-SIDE ROOM CREATION to ENABLED.
• Press the Save button.

Once that’s done, a Room for the specified type will be created as soon as a Participant SDK connects. For example, the following code snippet illustrates how to do this in JavaScript:

connect('$TOKEN', {name: 'myFancyRoomName' }).then(room => {
  console.log(`Successfully joined a Room: ${room}`);
  room.on('participantConnected', participant => {
    console.log(`A remote Participant connected: ${participant}`);
  });
}, error => {
  console.error(`Unable to connect to Room: ${error.message}`);
});

Notice that a Room name must be specified. Names of active Rooms must be unique. Hence, subsequent Participants connecting with that name will just join that Room instead of creating a new one.

Ad-hoc Rooms comply with the following:

• First join timeout: there isn’t any as the Room is just when the first participant connects.
• Last leave timeout: the Room is destroyed just after the last Participant leaves. No waiting time here.
• Max Participant duration: a Participant can be connected to the Room up to 4 hours. After that time the Participant is disconnected.
• Max Room duration: a Room may exist up to 24 hours from creation time. After that time the Room is destroyed and all participants get Disconnected.

Comparing REST vs. Ad-hoc Rooms

The following table illustrates the main differences between Ad-hoc Rooms and Rooms created using the REST API

Small vs. Regular Group Rooms

Small Group Rooms behaves functionally the same as Group Rooms with the exception that Small Group Rooms is limited to a maximum of 4 participants. The price for Group Room participant minutes is the same as Small Group Room participant minutes.

WebRTC Go Rooms or P2P Rooms or Group Rooms: Which Room Should I Use?

• In general Group Rooms provides the most functionality and flexibility. It supports multi-party calls of more than 2 participants, recordings, PSTN dial-in/dial-out and additional quality controls.

• If your use case is 2 participants, and you do not need recordings or PSTN support, and you need end-to-end encryption of the media for compliance reasons, then P2P Rooms will work well for you.

• WebRTC Go Rooms are designed for developers looking to launch their application as quickly as possible with minimal cost. These Rooms are functionally similar to P2P Rooms, however there is a scale limit of 100 participants in WebRTC Go Rooms at any instant in time.

次のステップ

Want to get started with Rooms? The following links may help you:

• Getting started with the Video JavaScript SDK
• Getting started with Android
• Getting started with iOS