Introduction

As of v3.0.0, the Agora Native RTC SDK enables users to join an unlimited number of channels at a time and to receive the audio and video streams of all the channels.

Sample project

Agora provides the following open-source sample projects on GitHub. You can download them and refer to the source code.

• MultiChannel
• Breakout Class

Implementation

The SDK uses the IChannel and IChannelEventHandler classes to support the multi-channel function.

You can call createChannel multiple times to create multiple IChannel objects with different channelId, and then call joinChannel in IChannel to join the channel.

The following are the major steps of implementing the multi-channel function:

1. Call createAgoraRtcEngine and initialize to create and initialize IRtcEngine.
2. Call setChannelProfile to set the channel profile as live streaming.
3. Call createChannel to create an IChannel object with a channelId.
4. Call setChannelEventHandler of the IChannel class to receive callbacks in this channel.
5. Call setClientRole of the IChannel class to set the user role.
6. Call joinChannel of the IChannel class to join the channel. After joining a channel, the user publishes the local streams and automatically subscribes to the streams of all the other users in the channel by default. You can set the publishing and subscribing states in ChannelMediaOptions when joining a channel, and you can change the publishing and subscribing states in the methods with prefixes muteLocaland muteRemote of the IChannel class after joining a channel.
7. Repeat steps 3, 4, 5, and 6 to join more channels.

API call sequence

Refer to the following API sequence to join multiple channels:

Sample code

The following code demonstrates how to join an IChannel channel, and then publish the local streams in the first channel.

1. Create and initialize IRtcEngine.

   m_rtcEngine = createAgoraRtcEngine();
   RtcEngineContext context;
   std::string strAppID = GET_APP_ID;
   context.appId = strAppID.c_str();
   m_eventHandler.SetMsgReceiver(m_hWnd);
   context.eventHandler = &m_eventHandler;
   int ret = m_rtcEngine->initialize(context);

2. Enable the video module.

   m_rtcEngine->enableVideo();

3. Set the channel profile as interactive live streaming.

   m_rtcEngine->setChannelProfile(CHANNEL_PROFILE_LIVE_BROADCASTING);

4. Create an IChannel1 object, and listen for events in this channel.

   IChannel * pChannel1 = static_cast<IRtcEngine2 *>(m_rtcEngine)->createChannel(szChannelId.c_str());
   ChannelEventHandler* pEvt = new ChannelEventHandler;
   pEvt->setMsgHandler(GetSafeHwnd());
   m_channels.emplace_back(szChannelId, pChannel1, pEvt);
   pChannel1->setChannelEventHandler(pEvt);

5. Set the user role as a host.

   pChannel1->setClientRole(CLIENT_ROLE_BROADCASTER);

6. Pass in token and channelId to join the IChannel1 channel. The SDK publishes the local streams and automatically subscribes to the streams of all the other users in the channel by default.

   ChannelMediaOptions options1;
   options1.autoSubscribeAudio = true;
   options1.autoSubscribeVideo = true;
   options1.publishLocalAudio = true;
   options1.publishLocalVideo = true;
   pChannel1->joinChannel(APP_TOKEN, "", 0, options1);

7. Create an IChannel2 object, and listen for events in this channel.

   IChannel * pChannel2 = static_cast<IRtcEngine2 *>(m_rtcEngine)->createChannel(szChannelId.c_str());
   ChannelEventHandler* pEvt = new ChannelEventHandler;
   pEvt->setMsgHandler(GetSafeHwnd());
   m_channels.emplace_back(szChannelId, pChannel2, pEvt);
   pChannel2->setChannelEventHandler(pEvt);

8. Set the user role as an audience member. Note that audience members cannot publish local streams.

   pChannel2->setClientRole(CLIENT_ROLE_AUDIENCE);

9. Pass in token and channelId to join the IChannel2 channel. You need to set publishLocalAudio and publishLocalVideo to false; otherwise, the user fails to join the channel.

   ChannelMediaOptions options2;
   options2.autoSubscribeAudio = true;
   options2.autoSubscribeVideo = true;
   options2.publishLocalAudio = false;
   options2.publishLocalVideo = false;
   pChannel2->joinChannel(APP_TOKEN, "", 0, options2)

10. Leave and destroy the IChannel2 channel.

    info.channel2->leaveChannel();
    info.channel2->release();

11. Leave and destroy the IChannel1 channel.

    info.channel1->leaveChannel();
    info.channel1->release();

12. Destroy the IRtcEngine object.

    m_rtcEngine->release(true);

API reference

• createChannel
• IChannel
• IChannelEventHandler

Considerations

Subscription limits

joinChannel in the IChannel class provides the media-subscription options (autoSubscribeAudio and autoSubscribeVideo) that determine whether to automatically subscribe to the remote streams after joining the channel. The default setting is to subscribe to all the streams automatically. After a user joins a channel, you can change the subscribing state by calling muteRemoteAudioStream or muteRemoteVideoStream.

If you need to subscribe to the streams of specified users after joining an IChannel channel, refer to the following steps:

1. Call joinChannel and set autoSubscribeAudio = false or autoSubscribeVideo = false of ChannelMediaOptions to unsubscribe from all remote users.
2. In the channel, call muteRemoteAudioStream (uid,false) or muteRemoteVideoStream(uid,false) to subscribe to specified remote users.

Set the remote video view

In video scenarios, if the remote user joins the channel using IChannel, ensure that you specify the channelId of the remote user in VideoCanvas when setting the remote video view.

Publishing limits

The SDK supports publishing local streams to only one channel at a time. Agora recommends setting the user role as an audience when joining a channel where the user do not need to publish streams, and setting publishLocalAudio and publishLocalVideo in ChannelMediaOptions to false when joining the channel.

In the interactive live streaming profile, if a user joins the first channel as a host, the SDK publishes local streams in the first channel by default. If the user needs to join a second channel, you need to change the publishing state according to your actual scenario:

• If the user does not need to publish local streams in the second channel, Agora recommends joining the second channel as an audience member (setClientRole(AUDIENCE)).
• If the user needs to publish local streams in the second channel, the user needs to stop publishing in the current channel before joining the second channel. Agora recommends setting the user role as an audience member (setClientRole(AUDIENCE)) in the first channel and joining the second channel as a host (setClientRole(BROADCASTER)).

If a user publishes local streams in a channel and you call the following methods in a second channel, the method call fails, and the SDK returns -5(ERR_REFUSED):

• Set publishLocalAudio = true or publishLocalVideo = true when joining the second channel.
• Call muteLocalAudioStream(false) or muteLocalVideoStream(false) after joining the second channel.
• Call setClientRole(BROADCASTER).

API changes

As of v3.4.5, the IChannel class changes as follows:

• Deprecates publish and unpublish, and adds muteLocalAudioStream and muteLocalVideoStream instead. After joining a channel, you can set the publishing state of the audio stream and video stream separately. muteLocalAudioStream and muteLocalVideoStream in the IRtcEngine and IChannel classes control the publishing state of each channel in their respective classes only.
• Adds the publishLocalAudio and publishLocalVideo members in ChannelMediaOptions. The default value is true. You can call joinChannel to join a channel and set the publishing state. If a user publishes streams in a channel, regardless of whether the user is a host or an audience member, they need to set publishLocalAudio and publishLocalVideo to false when joining other channels; otherwise, they fail to join the channel.
• After calling setClientRole(BROADCASTER), the local user publishes audio and video streams by default. You no longer need to call publish.

Earlier than v3.4.5:

• Calling muteLocalAudioStream(true) or muteLocalVideoStream(true) in IRtcEngine takes effect in channels created by both the IRtcEngine and IChannel classes. muteLocalAudioStream and muteLocalVideoStream take effect when they are called before or after a user joins a channel.
• joinChannel cannot set the publishing state of local streams.
• Calling setClientRole(BROADCASTER) of the IChannel class does not publish local streams. You also need to call publish.