Cross-channel media stream relay

Prerequisites

• Ensure that you have implemented the SDK quickstart in your project.
• Contact support@agora.io to activate the cross-channel media stream relay feature.

Implement cross-channel media stream relay

The following figure shows the workflow you implement to facilitate cross-channel media stream relay:

To implement cross-channel media stream relay in your app, take the following steps:

1. Start cross-channel media stream relay

   After joining a channel, call startOrUpdateChannelMediaRelay to configure the source and target channel information and start forwarding a media stream. Calling this method before joining a channel fails. In live broadcasting, only hosts can call this method.

   // Configure source channel information
   ChannelMediaInfo *m_srcInfo = new ChannelMediaInfo;
   m_srcInfo->channelName = new char[szChannelId.size() + 1];
   strcpy_s(const_cast<char *>(m_srcInfo->channelName), szChannelId.size() + 1,
   		szChannelId.data());
   // Note: The token for source channel is different from the token used when joining the source channel.
   // It needs to be regenerated using the source channel name and uid = 0
   m_srcInfo->token = APP_TOKEN;
   // It is recommended to set the uid of the source channel to 0, allowing the SDK to assign a random uid.
   m_srcInfo->uid = 0;
   
   // Configure destination channel information
   int nDestCount = m_vecChannelMedias.size();
   ChannelMediaInfo *lpDestInfos = new ChannelMediaInfo[nDestCount];
   for (int nIndex = 0; nIndex < nDestCount; nIndex++) {
   	lpDestInfos[nIndex].channelName = m_vecChannelMedias[nIndex].channelName;
   	lpDestInfos[nIndex].token = m_vecChannelMedias[nIndex].token;
   	// Set the uid to 0, allowing the SDK to assign a random uid, or specify your own uid
   	// Ensure that it is different from all uids in the target channels
   	lpDestInfos[nIndex].uid = m_vecChannelMedias[nIndex].uid;
   }
   
   ChannelMediaRelayConfiguration cmrc;
   cmrc.srcInfo = m_srcInfo;
   cmrc.destInfos = lpDestInfos;
   cmrc.destCount = nDestCount;
   int ret = 0;
   // Start or update the cross-channel media stream relay
   ret = m_rtcEngine->startOrUpdateChannelMediaRelay(cmrc);

   • Best practice is to set the UID of the source channel to 0, allowing the SDK to assign a random UID.
   • The source channel token in srcChannelInfo should be different from the one used when joining the source channel. Generate a new token using the source channel name and uid = 0.
   • For the destination channel, set the uid to 0, to allow the SDK to assign a random uid, or specify a uid, ensuring that it is different from all uids in the target channel.
   • Cross-channel media stream relay doesn't support String-type user IDs. Join the channel with an int-type uid.

2. Update media stream relay channels

   To forward the stream to multiple target channels or exit the current forwarding channel after starting channel media relay, call startOrUpdateChannelMediaRelay again to add or remove target channels for forwarding. Multiple hosts in a channel can forward media streams, and each host can forward to up to six target channels.

   The updated configuration completely replaces the previous configuration.

3. Pause or resume media stream relay

   To pause forwarding the media stream to all target channels, call pauseAllChannelMediaRelay.

   m_rtcEngine->pauseAllChannelMediaRelay();

   To resume forwarding the media stream to all target channels, call resumeAllChannelMediaRelay.

   m_rtcEngine->resumeAllChannelMediaRelay();

4. Stop cross-channel media stream relay

   To stop forwarding the media stream, call stopChannelMediaRelay . When forwarding stops, the host exits all target channels.

   m_rtcEngine->stopChannelMediaRelay();
   m_lstInfo.AddString(_T("stopChannelMediaRelay"));
   m_btnStartMediaRelay.SetWindowText(CrossChannelStartMediaRelay);

   If this method fails, you can call leaveChannel to leave the channel, and cross-channel media stream relay will automatically stop.

5. Listen for cross-channel media stream status changes

   During cross-channel media stream relay, the SDK reports changes in the status of media stream relay through the onChannelMediaRelayStateChanged callback. Implement relevant business logic based on the status codes.

   class CAgoraCrossChannelEventHandler : public IRtcEngineEventHandler {
       virtual void onChannelMediaRelayStateChanged(
           CHANNEL_MEDIA_RELAY_STATE state,
           CHANNEL_MEDIA_RELAY_ERROR code) override {
           if (m_hMsgHanlder)
               ::PostMessage(m_hMsgHanlder,
                   WM_MSGID(EID_CHANNEL_MEDIA_RELAY_STATE_CHNAGENED),
                   state, code);
       }
   };

Reference

This section contains content that completes the information on this page, or points you to documentation that explains other aspects to this product.

Status codes

The main media stream forwarding states and their corresponding status codes are as follows:

Sample project

Agora provides an open-source CrossChannel sample project for your reference. Download the project or view the source code for a more detailed example.

API reference

• startOrUpdateChannelMediaRelay
• stopChannelMediaRelay
• pauseAllChannelMediaRelay
• resumeAllChannelMediaRelay
• onChannelMediaRelayStateChanged
• ChannelMediaRelayConfiguration
• ChannelMediaInfo