Preload channels

This page explains how to implement channel preloading to achieve near-instant channel entry. By preloading channel information and media streams before users join, you can significantly reduce the time required to render the first video frame and create a smoother viewing experience.

The following video demonstrates the channel preload experience:

The following figure illustrates the best practice when preloading channels:

Following these guidelines, you can reduce the first frame loading time for Chrome browsers on Windows and macOS to as low as 300 milliseconds.

Implementation

Follow these steps to implement channel preloading:

Preload channel list

On the channel list page, preload the channels within the user's view area with the preload method.

If the total number of channels does not exceed 10, preload all channels.
If the total number of channels exceeds 10, preload only the first 10 channels. If the user scrolls the channel list, wait for the scrolling to stop, then preload the new channels in the user's view area.

To speed up the subsequent joining of the channel, use a wildcard token in the token parameter of the preload method.

Pre-join individual channels

Implement pre-joining for different mouse interactions:

Before entering the channel

When a user hovers over a channel, best practice is to join the channel and subscribe to audio and video before entering. The specific operations include the following:
- Call join to join the channel and subscribe to the host's audio and video streams.
- Render the video in advance in a small preview window.
To speed up joining the channel, use a wildcard token in the token parameter of the join method.

Entering the channel

To reduce the time it takes to render the first frame of the host's video, enable subscribing to the host's media stream as soon as the user enters the channel. When calling join, set autoSubscribe to true in options:

// Create client
const client = AgoraRTC.createClient({
    mode: "live",
    codec: "vp8",
    role: "host",
});

// Enables auto subscription when the client joins a channel
await client.join(APP_ID, CNAME, TOKEN, UID / null, {
    autoSubscribe: true,
});

The following table compares the steps from when a user enters the channel to when the host's media stream is rendered, before and after enabling this function:

Before	After
The user joins the channel. The channel sends the host/media information. The user subscribes to the media stream in the channel. The Agora backend starts sending the media stream in the channel. The user waits for the Agora backend to send the media stream, receives it, and renders it locally.	The user joins the channel. The Agora backend immediately sends the media stream in the channel. The channel sends the host/media information. After the user subscribes to the media stream, they can immediately receive and render the media stream locally.

Note

Joining a channel incurs additional fees due to the transmission of media streams. See Pricing for details.

When a user clicks on the channel in the list, take the following actions:

Switch the app interface from the channel list page to the single channel page. Best practice is to add a page switching animation.
Call IRemoteAudioTrack.play and IRemoteVideoTrack.play. The video needs to be passed in the specified DOM element.

Leaving without entering

When a user hovers over a channel but does not click to enter, best practice is to call leave.

Precautions

Wildcard tokens can speed up the process of joining a channel but may cause room overflow. Decide whether to use wildcard tokens based on your specific needs.
Pre-joining channels incurs additional charges.

In live streaming applications, a key user experience performance metric is how quickly a viewer can join or switch channels and how fast the remote video stream is rendered on their device. This document explores methods and best practices for reducing first-frame rendering time in apps using Video SDK and provides sample code for desktop and mobile devices.

Agora provides an open source VideoLoaderAPI sample project on GitHub that includes APIs for fast channel loading and switching. To integrate the APIs into your project, copy the following files from the videoloaderapi directory to your project:

videoloaderapi/
├── OnLiveRoomItemTouchEventHandler.kt
├── OnPageScrollEventHandler.kt
├── OnPageScrollEventHandler2.kt
├── OnRoomListScrollEventHandler.kt
├── VideoLoader.kt
└── VideoLoaderImpl.kt

Note

To facilitate future code upgrades, do not modify the names and paths of these files.

Follow these steps to implement fast channel joining and switching:

Prepare to use the VideoLoader API

Take the following steps before using the fast joining and fast switching features:

Initialize an RtcEngine instance.

Call the create method to create and initialize an RtcEngine instance:

// Initialize RtcEngine
private val mRtcEngine by lazy {
    RtcEngine.create(RtcEngineConfig().apply {
        mContext = applicationContext
        // Pass in the App Id you obtained from Agora console
        mAppId = BuildConfig.AGORA_APP_ID
        mEventHandler = object : IRtcEngineEventHandler() {}
    })
}

Use a wildcard token.

To speed up the process of users joining a channel, use a wildcard token. Generate the token on your server and pass it to the client for authentication.

Note
Using wildcard tokens carries security risks, such as room bombing. Evaluate whether wildcard tokens are appropriate for your use case before implementation.

:::

Fast channel joining

This section explains how to create a seamless, instant-opening experience in live broadcast scenarios.

Add a UI element for the live broadcast room list.

Implement a UI element to display a list of live broadcast rooms. The following example uses a RecyclerView:

<androidx.recyclerview.widget.RecyclerView
    android:id="@+id/rvRooms"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingHorizontal="7.5dp"
    android:overScrollMode="never"
    app:layoutManager="androidx.recyclerview.widget.GridLayoutManager"
    app:spanCount="2"
    android:clipToPadding="false"
    android:clipChildren="false"
    android:paddingBottom="50dp"
    android:visibility="visible" />

Listen for scrolling events.

Create an OnRoomListScrollEventHandler instance and register it as a proxy for live room list scroll events in the UI. To create the OnRoomListScrollEventHandler instance, pass the following parameters to its constructor:

mRtcEngine: A previously initialized RtcEngine instance.
localUid: The uid of the local user.

The OnRoomListScrollEventHandler listens for scroll events in the live broadcast room list and applies best practices encapsulated within the class. It preloads channels for live broadcast rooms that appear on the screen (preloadChannel).

// Code snippet from RoomListActivity
class RoomListActivity : AppCompatActivity() {
    private val mBinding by lazy { ShowRoomListActivityBinding.inflate(LayoutInflater.from(this)) }
    // Create an OnRoomListScrollEventHandler instance
    private val onRoomListScrollEventHandler: OnRoomListScrollEventHandler = object : OnRoomListScrollEventHandler(mRtcEngine, RtcEngineInstance.localUid()) {}
    // Business service module
    private val mService by lazy { ShowServiceProtocol.getImplInstance() }

    override fun onCreate(savedInstanceState: Bundle?) {
        // Set the OnRoomListScrollEventHandler instance to the live room list to listen for scroll events
        mBinding.rvRooms.addOnScrollListener(onRoomListScrollEventHandler as OnRoomListScrollEventHandler)

        // Get room List
        mService.getRoomList { roomList ->
            // After getting the room list, pass the result to the onRoomListScrollEventHandler instance
            onRoomListScrollEventHandler?.updateRoomList(roomList)
        }
    }
}

Listen for touch events.

Create an OnLiveRoomItemTouchEventHandler instance and register it as a proxy for touch events in a single live room UI. To create the OnLiveRoomItemTouchEventHandler instance, pass the following parameters to its constructor:

mRtcEngine: A previously initialized RtcEngine instance.
roomInfo: A VideoLoader.RoomInfo instance.

The OnLiveRoomItemTouchEventHandler instance listens for touch events in a live broadcast room and implements the best practices encapsulated within the class. When a user taps a live room, they enter it automatically. You do not need to explicitly call joinChannel or similar methods in the business layer.

// Code snippet from RoomListActivity
class RoomListActivity : AppCompatActivity() {
    private val mBinding by lazy { ShowRoomListActivityBinding.inflate(LayoutInflater.from(this)) }
    private lateinit var mRoomAdapter: BindingSingleAdapter<ShowRoomDetailModel, ShowRoomItemBinding>

    override fun onCreate(savedInstanceState: Bundle?) {
        mRoomAdapter = object : BindingSingleAdapter<ShowRoomDetailModel, ShowRoomItemBinding>() {
            override fun onBindViewHolder(
                holder: BindingViewHolder<ShowRoomItemBinding>,
                position: Int
            ) {
                // UI for individual live streams
                val roomInfo = getItem(position) ?: return
                // Create an OnLiveRoomItemTouchEventHandler instance
                val onTouchEventHandler = object : OnLiveRoomItemTouchEventHandler(
                    // Previously initialized RtcEngine instance
                    mRtcEngine,
                    // Room Information
                    VideoLoader.RoomInfo(
                        roomInfo.roomId,
                        arrayListOf(
                            VideoLoader.AnchorInfo(
                                roomInfo.roomId,
                                roomInfo.ownerId.toInt(),
                                // Token mentioned above
                                // Sample code for wildcard token
                                RtcEngineInstance.generalToken()
                            )
                        )
                    ),
                    RtcEngineInstance.localUid()
                ) {
                    override fun onTouch(v: View?, event: MotionEvent?): Boolean {
                        when (event!!.action) {
                            MotionEvent.ACTION_UP -> {
                                if (RtcEngineInstance.generalToken() != "") {
                                    super.onTouch(v, event)
                                    // Listen to the ACTION_UP event and go to the in-stream page
                                    goLiveDetailActivity(list, position, roomInfo)
                                }
                            }
                        }
                        return true
                    }

                    // Informs you to render the host screen
                    override fun onRequireRenderVideo(info: VideoLoader.AnchorInfo): VideoLoader.VideoCanvasContainer? {
                        // The best time to render the host screen
                        return ...
                    }
                }

                // Set the OnLiveRoomItemTouchEventHandler instance to a single live room to listen for touch events
                binding.root.setOnTouchListener(onTouchEventHandler)
            }
        }
        mBinding.rvRooms.adapter = mRoomAdapter
    }
}

The OnLiveRoomItemTouchEventHandler instance automatically adds the host screen to the container and renders it when it receives the onRequireRenderVideo event. To ensure smooth rendering, create a container for the host screen in advance and return it to the handler when the event occurs.

Fast channel switching

This section explains how to enable viewers to switch live broadcast channels quickly.

Implement a UI component for sliding between live broadcast rooms.

The following example uses a ViewPager2 element:

<androidx.viewpager2.widget.ViewPager2 xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/viewPager2"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:overScrollMode="never"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    app:layout_scrollEffect="none"
    android:layout_height="match_parent" />

Listen for live room switching events.

Create an OnPageScrollEventHandler instance and register it as the slide event proxy for the ViewPager2 live broadcast room. To create the OnPageScrollEventHandler instance, pass the following parameters to the constructor:

mRtcEngine: A previously initialized RtcEngine instance.
localUid: The uid of the local user.
needPreJoin: Determines whether to prejoin the adjacent live broadcast rooms (above and below the current one). Setting this to true improves instant switching but increases resource consumption.
sliceMode: Toggles the timing of outputting pictures in the live broadcast room.

The OnPageScrollEventHandler instance implements best practices for managing live broadcast rooms. It listens for the ViewPager2 slide event of the live broadcast room and optimally switches audio/video subscription behavior between rooms. It triggers the following events at the corresponding position:

onPageStartLoading: Just started loading/displaying the live broadcast room.
onPageLoaded: Live room loading/display completed
onPageLeft: Left the live broadcast room
onRequireRenderVideo: The best time to render the host view of the corresponding live broadcast room. At this time, pass in the container for the host screen of the corresponding live broadcast room. The OnPageScrollEventHandler instance adds and renders the host screen on the container.

// Code snippet from LiveViewPagerActivity
class LiveViewPagerActivity : AppCompatActivity() {
    private val mBinding by lazy { LiveViewPagerActivityBinding.inflate(LayoutInflater.from(this)) }
    // Use a circular array to store a list of live rooms that a user can switch between
    private val vpFragments = SparseArray<LiveViewPagerFragment>()
    // Create OnPageScrollEventHandler instance
    private var onPageScrollEventHandler: OnPageScrollEventHandler? = object : OnPageScrollEventHandler(
        // Previously initialized RtcEngine instance
        RtcEngineInstance.rtcEngine,
        // Local user's uid
        RtcEngineInstance.localUid(),
        // Set whether or not to join the two live rooms adjacent to the current live room ahead of time
        // If set to true, this results in faster switching, but at an increased cost
        needPreJoin,
        // Toggles the timing of the live feed out via the onPageScrollStateChanged event.
        sliceMode
    ) {
        override fun onPageScrollStateChanged(state: Int) {
            when (state) {
                ViewPager2.SCROLL_STATE_SETTLING -> binding.viewPager2.isUserInputEnabled = false
                ViewPager2.SCROLL_STATE_IDLE -> binding.viewPager2.isUserInputEnabled = true
            }
            super.onPageScrollStateChanged(state)
        }

        override fun onPageStartLoading(position: Int) {
            // Notify the corresponding position of the live room to start displaying
            vpFragments[position]?.startLoadPageSafely()
        }

        override fun onPageLoaded(position: Int) {
            // Notify the corresponding position that the live room has been displayed
            vpFragments[position]?.onPageLoaded()
        }

        override fun onPageLeft(position: Int) {
            // Notify the corresponding position that the live room has left
            vpFragments[position]?.stopLoadPage(true)
        }

        override fun onRequireRenderVideo(position: Int, info: VideoLoader.AnchorInfo): VideoLoader.VideoCanvasContainer? {
            // The best time to render the host screen of the corresponding live room, notify the live room of the corresponding position and return the container of the corresponding host screen.
            return vpFragments[position]?.initAnchorVideoView(info)
        }
    }

    // The actions that are performed when an Activity is created are described below.
    override fun onCreate(savedInstanceState: Bundle?) {
        // To be added
        ...
    }
}

Call updateRoomList when the Activity is created to pass the initial live broadcast room list to the onPageScrollEventHandler instance. Additionally, call onRoomCreated within the createFragment event of FragmentStateAdapter to notify onPageScrollEventHandler that the corresponding live room has been created. Add the following code inside override fun onCreate(savedInstanceState: Bundle?) {}:

override fun onCreate(savedInstanceState: Bundle?) {
    // When initializing the Activity, pass the initial live room list to the onPageScrollEventHandler instance
    onPageScrollEventHandler?.updateRoomList(list)

    // Set ViewPager2 to keep at least one page (Fragment) on each side of the current page in memory
    binding.viewPager2.offscreenPageLimit = 1

    // Create a FragmentStateAdapter to manage pages representing live rooms
    val fragmentAdapter = object : FragmentStateAdapter(this) {
        // If ViewPager2 allows sliding, it holds an infinite number of pages
        // Otherwise, it returns 1, holding only a single page.
        override fun getItemCount() = if (mScrollable) Int.MAX_VALUE else 1

        // Create a LiveViewPagerFragment for each live feed
        override fun createFragment(position: Int): Fragment {
            val roomInfo = if (mScrollable) {
                mRoomInfoList[position % mRoomInfoList.size]
            } else {
                mRoomInfoList[selectedRoomIndex]
            }
            return LiveViewPagerFragment.newInstance(
                roomInfo,
                onPageScrollEventHandler as OnPageScrollEventHandler, position
            ).apply {
                // Store the created LiveViewPagerFragment in vpFragments
                vpFragments.put(position, this)

                // Create a list of hosts for the live room
                val anchorList = arrayListOf(
                    VideoLoader.AnchorInfo(
                        roomInfo.roomId,
                        roomInfo.ownerId.toInt(),
                        RtcEngineInstance.generalToken()
                    )
                )

                // Notify onPageScrollEventHandler that the corresponding room has been created
                onPageScrollEventHandler?.onRoomCreated(
                    position,
                    VideoLoader.RoomInfo(roomInfo.roomId, hostList),
                    position == binding.viewPager2.currentItem
                )
            }
        }
    }
    binding.viewPager2.adapter = fragmentAdapter

    // Set whether the user can manually swipe pages
    // In a typical live room scenario, viewers can swipe manually, but hosts cannot.
    binding.viewPager2.isUserInputEnabled = mScrollable

    if (mScrollable) {
        // If swiping is enabled:
        // - Register the OnPageScrollEventHandler instance to listen for page change events
        // - Calculate the latest position
        binding.viewPager2.registerOnPageChangeCallback(
            onPageScrollEventHandler as OnPageChangeCallback
        )
        binding.viewPager2.setCurrentItem(
            Int.MAX_VALUE / 2 - Int.MAX_VALUE / 2 % mRoomInfoList.size + selectedRoomIndex,
            false
        )
    } else {
        // If swiping is disabled, set the current position to 0
        currLoadPosition = 0
    }
}

Release resources

After using the VideoLoaderAPI, you do not need to call leaveChannel in the business layer to leave the live broadcast. To release resources, refer to the following sample code:

VideoLoader.getImplInstance(mRtcEngine).cleanCache()
VideoLoader.release()
RtcEngineEx.destroy()

Agora provides an open source VideoLoaderAPI sample project on GitHub that includes APIs for fast channel loading and switching. To integrate the APIs into your project, take the following steps:

Copy the following folders and files from the repository to the same folder as your *.xcodeproj file:
- VideoLoaderAPI folder
- VideoLoaderAPI.podspec file
Note
To facilitate subsequent code upgrades, do not modify the names and paths of the files you add.

:::

In the terminal, go to the directory where the *.xcodeproj file is located and run the pod init command. A Podfile text file is generated in the project folder.

Open the Podfile file and modify it as follows:

source 'https://github.com/CocoaPods/Specs.git'
use_frameworks!

platform :ios, '13.0'

# Change the target to the actual Target name in your project.
target 'VideoLoaderAPI_Example' do
pod 'VideoLoaderAPI', :path => 'VideoLoaderAPI.podspec'

    target 'VideoLoaderAPI_Tests' do
        inherit! :search_paths
    end
end

In the terminal, go to the directory where the *.xcodeproj file is located and execute pod install to install the dependencies.

After successful installation of the dependency library, you see a *.xcworkspace file.

(Optional) If you have previously integrated a Video SDK dependency in your project, open the VideoLoaderAPI.podspec file and modify the dependency version as needed.

# 4.1.1.19 is the default version installed in step 4, if you are using a different version, change it to the current one.
s.dependency 'AgoraRtcEngine_Special_iOS', '4.1.1.19'

Follow these steps to implement fast channel joining and switching:

Prepare to use the VideoLoader API

Take the following steps before using the fast joining and fast switching features:

Initialize AgoraRtcEngineKit and VideoLoader instances.

In the default ViewController of the project file, call the sharedEngine(with:) method of Video SDK to create and initialize an AgoraRtcEngineKit instance. Then, initialize the VideoLoader.

func prepareEngine() {
    // Create an Instance of AgoraRtcEngineKit
    let engine = _createRtcEngine()
    // Obtain a shared instance of VideoLoaderApiImpl
    let loader = VideoLoaderApiImpl.shared
    loader.addListener(listener: self)
    // Creating a VideoLoaderConfig instance
    let config = VideoLoaderConfig()
    // Setting up an AgoraRtcEngineKit instance
    config.rtcEngine = engine
    // Initialize VideoLoader
    loader.setup(config: config)
}

// Initializing AgoraRtcEngineKit
private func _createRtcEngine() -> AgoraRtcEngineKit {
    let config = AgoraRtcEngineConfig()
    // Use the App Id of your project from the console
    config.appId = KeyCenter.AppId
    config.channelProfile = .liveBroadcasting
    config.audioScenario = .gameStreaming
    config.areaCode = .global
    let engine = AgoraRtcEngineKit.sharedEngine(with: config,
                                                delegate: nil)
    return engine
}

Use a wildcard token.

To speed up the process of users joining a channel, use a wildcard token. Generate the token on your server and pass it to the client for authentication.

Note
Using wildcard tokens carries security risks, such as room bombing. Evaluate whether wildcard tokens are appropriate for your use case before implementation.

:::

Fast channel joining

This section explains how to create a seamless, instant-opening experience in live broadcast scenarios.

Add a UI component for the live broadcast room list.

Implement a UI component to display a list of live broadcast rooms. The following example uses a UICollectionView:

private lazy var listView: UICollectionView = {
    let layout = UICollectionViewFlowLayout()
    layout.minimumLineSpacing = 5
    layout.minimumInteritemSpacing = 5
    layout.sectionInset = .zero

    let w = view.bounds.width / 2 - 5
    layout.itemSize = CGSize(width: w, height: w * 1.5)

    let collectionView = UICollectionView(frame: self.view.bounds, collectionViewLayout: layout)
    collectionView.backgroundColor = .white
    collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: "videoloader_listcell")
    collectionView.scrollsToTop = false
    collectionView.delegate = self.delegateHandler
    collectionView.dataSource = self
    collectionView.contentInsetAdjustmentBehavior = .never
    collectionView.showsVerticalScrollIndicator = false

    return collectionView
}()

Listen for scrolling events.

Create an instance of AGCollectionLoadingDelegateHandler and assign it as the delegate for the live room list UI to handle scrolling events. When initializing the AGCollectionLoadingDelegateHandler instance, pass the local user's uid in the localUid parameter of the constructor.

The AGCollectionLoadingDelegateHandler listens for scrolling events in the live broadcast room list and automatically preloads the live room channels that come into view (preloadChannel). This improves loading speed and enhances the user experience.

// The following code is from the ViewController for the live room list.
class ShowRoomListVC: UIViewController {
    // Create an instance of AGCollectionLoadingDelegateHandler.
    private lazy var delegateHandler: AGCollectionLoadingDelegateHandler = {
        let handler = AGCollectionLoadingDelegateHandler(localUid: localUid)
        return handler
    }()
    // Business service module for managing room data.
    private lazy var service: ShowServiceProtocol = AppContext.showServiceImp("")
    // List of live rooms
    private var roomList = [ShowRoomListModel]() {
        didSet {
            // Update delegateHandler with the latest room list
            delegateHandler.roomList = AGRoomArray(roomList: roomList)
            collectionView.reloadData()
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // Perform any additional setup after loading the view.
        // ...

        prepareEngine()

        // Set delegate and data source for the room list UI.
        listView.delegate = self.delegateHandler
        listView.dataSource = self

        // Fetch the live room list from the service.
        service.getRoomList(page: 1) { [weak self] error, roomList in
            self?.roomList = roomList ?? []
        }
    }
}

Listen for touch events.

In the DataSource protocol of the native listView, create a Cell inside the cellForItemAt method. When initializing the Cell, use the ag_addPreloadTap method to listen for touch events on a specific live broadcast room.

When calling ag_addPreloadTap, provide the following parameters:

roomInfo: A VideoLoader.RoomInfo instance containing details of the live room.
localUid: The uid of the local user.
enableProcess: A callback function triggered when the user taps the Cell. Use this function to implement business logic, such as verifying whether the token has been successfully obtained.
onRequireRenderVideo: A callback function that handles rendering the host's video feed. It is recommended to create the video container in advance and assign the returned object to it when the onRequireRenderVideo event is triggered. This ensures that ag_addPreloadTap automatically attaches and renders the host’s video on the designated container.
completion: A callback function executed when the user enters the live broadcast page.

When a user taps a live broadcast room, ag_addPreloadTap automatically follows best practices, including joining the selected live broadcast channel. Consequently, you do not need to manually call joinChannelByToken or similar methods to handle channel joining within your business logic.

// The code snippet comes from the ViewController for the list of live streams.
extension ShowRoomListVC: UICollectionViewDataSource {
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        // Return the total number of rooms in the room list
        return roomList.count
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell: ShowRoomListCell = collectionView.dequeueReusableCell(withReuseIdentifier: NSStringFromClass(ShowRoomListCell.self), for: indexPath) as! ShowRoomListCell
        // Get the room data corresponding to the current index
        let room = roomList[indexPath.item]

        // Configure the Cell with room details
        // ...

        // Add a touch event to handle user interaction
        cell.ag_addPreloadTap(roomInfo: room, localUid: delegateHandler.localUid) { [weak self] state in
            if AppContext.shared.rtcToken?.count ?? 0 == 0 {
                // If no token has been obtained
                if state == .began {
                    // If the touch event starts (pressing down), retrieve a new token
                    self?.preGenerateToken()
                } else if state == .ended {
                    // If the touch event completes but the token is still unavailable, prevent the user from entering the live room
                    ToastView.show(text: "Token does not exist, try again!")
                }
                return false
            }
            return true
        } onRequireRenderVideo: { _ in
            // Provide a container for rendering the host's video feed (if available)
            return nil
        } completion: { [weak self] in
            // Enter the live stream
            self?.joinRoom(room)
        }

        return cell
    }
}

Fast channel switching

This section explains how to enable viewers to switch live broadcast channels quickly.

Implement a UI component for sliding between live broadcast rooms.

The following example uses a UICollectionView:

private lazy var collectionView: UICollectionView = {
    let layout = UICollectionViewFlowLayout()
    layout.minimumLineSpacing = 0
    layout.minimumInteritemSpacing = 0
    layout.sectionInset = .zero
    layout.itemSize = self.view.bounds.size
    let collectionView = UICollectionView(frame: self.view.bounds, collectionViewLayout: layout)
    collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: NSStringFromClass(UICollectionViewCell.self))
    collectionView.scrollsToTop = false
    collectionView.isPagingEnabled = true
    collectionView.contentInsetAdjustmentBehavior = .never
    collectionView.bounces = false
    collectionView.showsVerticalScrollIndicator = false
    return collectionView
}()

Listen for live room switching events.

Create an AGCollectionSlicingDelegateHandler instance and register it as the slide event delegate for the CollectionView live broadcast room. To create the AGCollectionSlicingDelegateHandler instance, pass the following parameters to the constructor:

localUid: uid of the local user.
needPreJoin: Determines whether to prejoin the adjacent live broadcast rooms (above and below the current one). Setting this to true improves instant switching but increases resource consumption.
videoType: Switch the timing of live broadcast room video display.
audioType: Switch the timing of the live broadcast room audio display.
onRequireRenderVideo: The callback function to render the host view of the corresponding live broadcast room. At this time, pass in the container for the host screen of the corresponding live broadcast room. The AGCollectionSlicingDelegateHandler instance adds and renders the host screen on that container.

The AGCollectionSlicingDelegateHandler instance listens to the CollectionView slide event of the live broadcast room. It implements the best practices encapsulated in the AGCollectionSlicingDelegateHandler class and switches the audio/video subscription behavior of different live broadcast rooms at the best time.

When creating the ViewController, call the roomList method to pass the initial live broadcast room list information to the AGCollectionSlicingDelegateHandler instance.

// The code snippet comes from the ViewController for the room list
class ShowLivePagesViewController: ViewController {
    // Creating an AGCollectionSlicingDelegateHandler instance
    private lazy var delegateHandler = {
        let handler = AGCollectionSlicingDelegateHandler(localUid: localUid, needPrejoin: needPrejoin)
        handler.videoSlicingType = videoType
        handler.audioSlicingType = audioType
        handler.onRequireRenderVideo = { [weak self] info, cell, indexPath in
            // Perform the appropriate action at the optimal time to render the host screen
            return ...
        }
        return handler
    }()

    // Pass the initial live room list information to the AGCollectionSlicingDelegateHandler instance
    var roomList: [ShowRoomListModel]? {
        didSet {
            delegateHandler.roomList = AGRoomArray(roomList: roomList)
        }
    }

    // Register the delegateHandler instance as the slide event proxy for the CollectionView in the live streaming room
    override func viewDidLoad() {
        super.viewDidLoad()

        // Setting up a proxy
        collectionView.delegate = delegateHandler
        collectionView.dataSource = self
        ...
    }
}

Release resources

After using the VideoLoaderAPI, you do not need to call leaveChannel in the business layer to leave the live broadcast. To release resources, refer to the following sample code:

VideoLoaderApiImpl.shared.cleanCache()
AgoraRtcEngineKit.destroy()

Agora provides an open source VideoLoaderAPI sample project on GitHub that includes APIs for fast channel loading and switching. To integrate the APIs into your project, take the following steps:

Copy the following folders and files from the repository to the same folder as your *.xcodeproj file:
- VideoLoaderAPI folder
- VideoLoaderAPI.podspec file
Note
To facilitate subsequent code upgrades, do not modify the names and paths of the files you add.

:::

In the terminal, go to the directory where the *.xcodeproj file is located and run the pod init command. A Podfile text file is generated in the project folder.

Open the Podfile file and modify it as follows:

source 'https://github.com/CocoaPods/Specs.git'
use_frameworks!

platform :ios, '13.0'

# Change the target to the actual Target name in your project.
target 'VideoLoaderAPI_Example' do
pod 'VideoLoaderAPI', :path => 'VideoLoaderAPI.podspec'

    target 'VideoLoaderAPI_Tests' do
        inherit! :search_paths
    end
end

In the terminal, go to the directory where the *.xcodeproj file is located and execute pod install to install the dependencies.

After successful installation of the dependency library, you see a *.xcworkspace file.

(Optional) If you have previously integrated a Video SDK dependency in your project, open the VideoLoaderAPI.podspec file and modify the dependency version as needed.

# 4.1.1.19 is the default version installed in step 4, if you are using a different version, change it to the current one.
s.dependency 'AgoraRtcEngine_Special_iOS', '4.1.1.19'

Follow these steps to implement fast channel joining and switching:

Prepare to use the VideoLoader API

Take the following steps before using the fast joining and fast switching features:

Initialize AgoraRtcEngineKit and VideoLoader instances.

In the default ViewController of the project file, call the sharedEngine(with:) method of Video SDK to create and initialize an AgoraRtcEngineKit instance. Then, initialize the VideoLoader.

func prepareEngine() {
    // Create an Instance of AgoraRtcEngineKit
    let engine = _createRtcEngine()
    // Obtain a shared instance of VideoLoaderApiImpl
    let loader = VideoLoaderApiImpl.shared
    loader.addListener(listener: self)
    // Creating a VideoLoaderConfig instance
    let config = VideoLoaderConfig()
    // Setting up an AgoraRtcEngineKit instance
    config.rtcEngine = engine
    // Initialize VideoLoader
    loader.setup(config: config)
}

// Initializing AgoraRtcEngineKit
private func _createRtcEngine() -> AgoraRtcEngineKit {
    let config = AgoraRtcEngineConfig()
    // Use the App Id of your project from the console
    config.appId = KeyCenter.AppId
    config.channelProfile = .liveBroadcasting
    config.audioScenario = .gameStreaming
    config.areaCode = .global
    let engine = AgoraRtcEngineKit.sharedEngine(with: config,
                                                delegate: nil)
    return engine
}

Use a wildcard token.

To speed up the process of users joining a channel, use a wildcard token. Generate the token on your server and pass it to the client for authentication.

Note
Using wildcard tokens carries security risks, such as room bombing. Evaluate whether wildcard tokens are appropriate for your use case before implementation.

:::

Fast channel joining

This section explains how to create a seamless, instant-opening experience in live broadcast scenarios.

Add a UI component for the live broadcast room list.

Implement a UI component to display a list of live broadcast rooms. The following example uses a UICollectionView:

private lazy var listView: UICollectionView = {
    let layout = UICollectionViewFlowLayout()
    layout.minimumLineSpacing = 5
    layout.minimumInteritemSpacing = 5
    layout.sectionInset = .zero

    let w = view.bounds.width / 2 - 5
    layout.itemSize = CGSize(width: w, height: w * 1.5)

    let collectionView = UICollectionView(frame: self.view.bounds, collectionViewLayout: layout)
    collectionView.backgroundColor = .white
    collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: "videoloader_listcell")
    collectionView.scrollsToTop = false
    collectionView.delegate = self.delegateHandler
    collectionView.dataSource = self
    collectionView.contentInsetAdjustmentBehavior = .never
    collectionView.showsVerticalScrollIndicator = false

    return collectionView
}()

Listen for scrolling events.

// The following code is from the ViewController for the live room list.
class ShowRoomListVC: UIViewController {
    // Create an instance of AGCollectionLoadingDelegateHandler.
    private lazy var delegateHandler: AGCollectionLoadingDelegateHandler = {
        let handler = AGCollectionLoadingDelegateHandler(localUid: localUid)
        return handler
    }()
    // Business service module for managing room data.
    private lazy var service: ShowServiceProtocol = AppContext.showServiceImp("")
    // List of live rooms
    private var roomList = [ShowRoomListModel]() {
        didSet {
            // Update delegateHandler with the latest room list
            delegateHandler.roomList = AGRoomArray(roomList: roomList)
            collectionView.reloadData()
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // Perform any additional setup after loading the view.
        // ...

        prepareEngine()

        // Set delegate and data source for the room list UI.
        listView.delegate = self.delegateHandler
        listView.dataSource = self

        // Fetch the live room list from the service.
        service.getRoomList(page: 1) { [weak self] error, roomList in
            self?.roomList = roomList ?? []
        }
    }
}

Listen for touch events.

When calling ag_addPreloadTap, provide the following parameters:

roomInfo: A VideoLoader.RoomInfo instance containing details of the live room.
localUid: The uid of the local user.
enableProcess: A callback function triggered when the user taps the Cell. Use this function to implement business logic, such as verifying whether the token has been successfully obtained.
onRequireRenderVideo: A callback function that handles rendering the host's video feed. It is recommended to create the video container in advance and assign the returned object to it when the onRequireRenderVideo event is triggered. This ensures that ag_addPreloadTap automatically attaches and renders the host’s video on the designated container.
completion: A callback function executed when the user enters the live broadcast page.

// The code snippet comes from the ViewController for the list of live streams.
extension ShowRoomListVC: UICollectionViewDataSource {
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        // Return the total number of rooms in the room list
        return roomList.count
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell: ShowRoomListCell = collectionView.dequeueReusableCell(withReuseIdentifier: NSStringFromClass(ShowRoomListCell.self), for: indexPath) as! ShowRoomListCell
        // Get the room data corresponding to the current index
        let room = roomList[indexPath.item]

        // Configure the Cell with room details
        // ...

        // Add a touch event to handle user interaction
        cell.ag_addPreloadTap(roomInfo: room, localUid: delegateHandler.localUid) { [weak self] state in
            if AppContext.shared.rtcToken?.count ?? 0 == 0 {
                // If no token has been obtained
                if state == .began {
                    // If the touch event starts (pressing down), retrieve a new token
                    self?.preGenerateToken()
                } else if state == .ended {
                    // If the touch event completes but the token is still unavailable, prevent the user from entering the live room
                    ToastView.show(text: "Token does not exist, try again!")
                }
                return false
            }
            return true
        } onRequireRenderVideo: { _ in
            // Provide a container for rendering the host's video feed (if available)
            return nil
        } completion: { [weak self] in
            // Enter the live stream
            self?.joinRoom(room)
        }

        return cell
    }
}

Fast channel switching

This section explains how to enable viewers to switch live broadcast channels quickly.

Implement a UI component for sliding between live broadcast rooms.

The following example uses a UICollectionView:

private lazy var collectionView: UICollectionView = {
    let layout = UICollectionViewFlowLayout()
    layout.minimumLineSpacing = 0
    layout.minimumInteritemSpacing = 0
    layout.sectionInset = .zero
    layout.itemSize = self.view.bounds.size
    let collectionView = UICollectionView(frame: self.view.bounds, collectionViewLayout: layout)
    collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: NSStringFromClass(UICollectionViewCell.self))
    collectionView.scrollsToTop = false
    collectionView.isPagingEnabled = true
    collectionView.contentInsetAdjustmentBehavior = .never
    collectionView.bounces = false
    collectionView.showsVerticalScrollIndicator = false
    return collectionView
}()

Listen for live room switching events.

localUid: uid of the local user.
needPreJoin: Determines whether to prejoin the adjacent live broadcast rooms (above and below the current one). Setting this to true improves instant switching but increases resource consumption.
videoType: Switch the timing of live broadcast room video display.
audioType: Switch the timing of the live broadcast room audio display.
onRequireRenderVideo: The callback function to render the host view of the corresponding live broadcast room. At this time, pass in the container for the host screen of the corresponding live broadcast room. The AGCollectionSlicingDelegateHandler instance adds and renders the host screen on that container.

When creating the ViewController, call the roomList method to pass the initial live broadcast room list information to the AGCollectionSlicingDelegateHandler instance.

// The code snippet comes from the ViewController for the room list
class ShowLivePagesViewController: ViewController {
    // Creating an AGCollectionSlicingDelegateHandler instance
    private lazy var delegateHandler = {
        let handler = AGCollectionSlicingDelegateHandler(localUid: localUid, needPrejoin: needPrejoin)
        handler.videoSlicingType = videoType
        handler.audioSlicingType = audioType
        handler.onRequireRenderVideo = { [weak self] info, cell, indexPath in
            // Perform the appropriate action at the optimal time to render the host screen
            return ...
        }
        return handler
    }()

    // Pass the initial live room list information to the AGCollectionSlicingDelegateHandler instance
    var roomList: [ShowRoomListModel]? {
        didSet {
            delegateHandler.roomList = AGRoomArray(roomList: roomList)
        }
    }

    // Register the delegateHandler instance as the slide event proxy for the CollectionView in the live streaming room
    override func viewDidLoad() {
        super.viewDidLoad()

        // Setting up a proxy
        collectionView.delegate = delegateHandler
        collectionView.dataSource = self
        ...
    }
}

Release resources

After using the VideoLoaderAPI, you do not need to call leaveChannel in the business layer to leave the live broadcast. To release resources, refer to the following sample code:

VideoLoaderApiImpl.shared.cleanCache()
AgoraRtcEngineKit.destroy()

Implementation

Preload channel list

Pre-join individual channels

Precautions

Prepare to use the VideoLoader API

Fast channel joining

Fast channel switching

Release resources

Prepare to use the VideoLoader API

Fast channel joining

Fast channel switching

Release resources

Prepare to use the VideoLoader API

Fast channel joining

Fast channel switching

Release resources

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