Key concepts

SRTC instance

Create an instance with new SRTC(initParams); almost all operations are exposed through this instance.

One instance can call join multiple times to join several channels at once; each join returns that channel’s Channel object
In-channel events are delivered through the srtc.onNotifyChannelEvent callback; with multiple channels, use each channel’s channel.onNotifyEvent to tell them apart. See Multi-channel (Chinese)

import { SRTC, LogLevel, LogTarget } from '@seastart/srtc-web-sdk';

const srtc = new SRTC({
  logLevel: LogLevel.DEBUG,   // DEBUG is recommended during development
  logTarget: LogTarget.CONSOLE,
});

Channel and token

A channel is the container for a multi-user audio and video session, uniquely identified by its channel name. Users who join the same channel can send and receive audio and video streams with each other. A token is the credential for joining a channel. Your server issues it through the STMLink server API, and it carries the channel name, user ID, permissions, and other information. Every join requires a valid token.

// After getting the token from your backend, call join; it returns a Channel object
const channel = await srtc.join(token);
console.log(channel.getInfo().channel); // Channel name

You can perform channel-level operations such as publishing, subscribing, and leaving directly on the Channel object returned by join. Single-channel apps don’t need to care about it—the srtc instance keeps all channel-level methods (internally acting on the current channel); you only need it to specify the target when you join multiple channels at once. See Multi-channel (Chinese). After joining, you can get channel and user information at any time with these methods:

// Get the current channel's info
const channelInfo = srtc.getChannelInfo();

// Get info for a user in the channel
const userInfo = srtc.getUserInfo(uid);

// Get all users in the channel (as a map)
const usersMap = srtc.getUsersInfo(true);   // Record<uid, UserInfo>

// Get all users in the channel (as an array)
const usersArr = srtc.getUsersInfo(false);  // UserInfo[]

Track system

A track is the smallest unit of audio and video data; each audio or video stream is a track.

Class hierarchy

BaseTrack
├── LocalAudioTrack          ← Local audio base class (custom audio stream)
│   └── LocalMicTrack        ← Microphone stream
├── LocalVideoTrack          ← Local video base class (custom video stream)
│   ├── LocalCameraTrack     ← Camera stream
│   └── LocalScreenTrack     ← Screen sharing stream
├── RemoteAudioTrack         ← Single remote audio stream
│   └── RemoteAudioMixTrack  ← Remote channel-wide mixed audio stream
└── RemoteVideoTrack         ← Remote video stream

Track types

Track type	How to create	Description
`LocalMicTrack`	`srtc.createLocalMicTrack()`	Microphone capture, supports switching devices
`LocalCameraTrack`	`srtc.createLocalCameraTrack()`	Camera capture, supports switching devices
`LocalScreenTrack`	`srtc.createLocalScreenTrack()`	Screen sharing, can capture system audio at the same time
`LocalAudioTrack`	`srtc.createLocalCustomAudioTrack(msTrack)`	Custom audio, pass in a `MediaStreamTrack`
`LocalVideoTrack`	`srtc.createLocalCustomVideoTrack(msTrack)`	Custom video, pass in a `MediaStreamTrack`
`RemoteAudioMixTrack`	`srtc.subscribeRemoteAudioMixTrack()`	Channel-wide mixed audio; in most scenarios this is the only audio you need to subscribe to
`RemoteAudioTrack`	`srtc.subscribeRemoteAudioTrack(uid, id)`	Subscribe to a single audio track of a given user
`RemoteVideoTrack`	`srtc.subscribeRemoteVideoTrack(uid, id)`	Subscribe to a given user’s video

Local track lifecycle

createLocalXxxTrack()
  → startCapture()        // Start capture (requests camera/microphone permission)
  → publishLocalTrack()   // Publish to the channel (other users can subscribe)
  → unpublishLocalTrack() // Unpublish (other users can't see it, but local capture continues)
  → stopCapture()         // Stop capture and release the device

Event system

SRTC provides two sets of event callbacks:

In-channel events (onNotifyChannelEvent)

Listen for channel connection state, remote users joining and leaving, remote track changes, local device state, and more:

srtc.onNotifyChannelEvent = (evt: ChannelEvent) => {
  switch (evt.type) {
    case ChannelEventType.USER_JOIN:
      // A remote user joined; evt.data is UserInfo
      break;
    case ChannelEventType.USER_TRACK_ADD:
      // A remote user published a new track; evt.data is { user: UserInfo, track: TrackInfo }
      break;
    // ... for more events, see "Events"
  }
};

Out-of-channel message events (onNotifyImEvent)

Listen for IM messages (call srtc.enableIm(token) first to enable IM):

srtc.onNotifyImEvent = (evt: ImEvent) => {
  if (evt.type === ImEventType.IM_MSG) {
    // evt.data is ImMsgData
  }
};

For the full event list, see Events (Chinese).

Audience mode (is_audience)

When UserInfo.is_audience is true, the user has joined the channel as an audience member:

Audience members only receive audio and video streams and can’t publish local tracks
Whether a user joins as audience is decided when the server issues the token
Use the ChannelEventType.ME_UPDATE event to detect changes to your own audience status

Overview

Web SDK

Android SDK

Swift SDK (iOS/macOS)

Python SDK (server-side AI)

Server API

SRTC instance

Channel and token

Track system

Class hierarchy

Track types

Local track lifecycle

Event system

In-channel events (onNotifyChannelEvent)

Out-of-channel message events (onNotifyImEvent)

Audience mode (is_audience)

​SRTC instance

​Channel and token

​Track system

​Class hierarchy

​Track types

​Local track lifecycle

​Event system

​In-channel events (onNotifyChannelEvent)

​Out-of-channel message events (onNotifyImEvent)

​Audience mode (is_audience)

SRTC instance

Channel and token

Track system

Class hierarchy

Track types

Local track lifecycle

Event system

In-channel events (onNotifyChannelEvent)

Out-of-channel message events (onNotifyImEvent)

Audience mode (is_audience)