# Optimize video rendering (/en/realtime-media/interactive-live-streaming/build/optimize-quality-and-connection/optimize-frame-rendering/android)

> For AI agents: see the complete documentation index at [llms.txt](/llms.txt).

First frame output time is the duration between when a user joins a channel and when they first see the remote video. A shorter first frame output time reduces perceived wait time by rendering video more quickly.

    This guide describes two best practices to reduce video rendering time in Interactive Live Streaming.

    ## Prerequisites [#prerequisites]

    Complete the steps in the [SDK Quickstart](/en/realtime-media/interactive-live-streaming/quickstart) to build a basic Interactive Live Streaming app.

    ## Understand the tech [#understand-the-tech]

    To reduce video rendering time, Agora provides the following solutions:

    * **Preload and initialize before joining the channel**
      Complete time-consuming operations ahead of time, such as preloading the channel, configuring the rendering view, and enabling accelerated rendering for audio and video frames.

    * **Join early, subscribe later**
      Join the channel in advance but delay subscribing to the audio and video stream. When the user triggers the join operation, subscribe to the host's stream and begin rendering immediately.

    The following table compares both solutions:

    | Characteristic       | Preload and initialize early                           | Join early, subscribe on demand                                        |
    | -------------------- | ------------------------------------------------------ | ---------------------------------------------------------------------- |
    | Applicable scenarios | Most audio and video use cases                         | Scenarios with very high requirements for first frame rendering speed  |
    | Core implementation  | Initialize and configure video settings before joining | Join the channel early without subscribing; subscribe only when needed |
    | Cost                 | Normal billing                                         | May incur additional channel usage fees                                |

    The following figure shows the time to output the first frame before optimization and with each solution:

    ![Optimize video rendering](https://assets-docs.agora.io/images/video-sdk/optimize-video-rendering-tech.jpg)

    ## Implement fast first-frame rendering [#implement-fast-first-frame-rendering]

    This section describes the implementation logic for both solutions.

    <Tabs defaultValue="preload">
      <TabsList>
        <TabsTrigger value="preload">
          Preload and initialize early
        </TabsTrigger>

        <TabsTrigger value="subscribe">
          Join early, subscribe on demand
        </TabsTrigger>
      </TabsList>

      <TabsContent value="preload">
        The following figure illustrates the essential steps:

        ### Sequence diagram for implementation [#sequence-diagram-for-implementation]

        ![Sequence diagram for optimized video rendering](https://assets-docs.agora.io/images/video-sdk/optimize-video-rendering-solution-1.svg)

        ### Set up a Video SDK instance [#set-up-a-video-sdk-instance]

        Creating and initializing the Video SDK engine takes time. To reduce first-frame display time, Agora recommends initializing the engine when the module is loaded, not when SDK functions are first called.

        <CalloutContainer type="info">
          <CalloutDescription>
            Initialize the engine only once. Avoid creating and destroying it multiple times.
          </CalloutDescription>
        </CalloutContainer>

        ```kotlin
        class AgoraQuickStartActivity : AppCompatActivity() {
            private var mRtcEngine: RtcEngine? = null

            override fun onCreate(savedInstanceState: Bundle?) {
                super.onCreate(savedInstanceState)

                // Create and initialize the engine during activity creation
                initializeAgoraEngine()
            }

            private fun initializeAgoraEngine() {
                try {
                    val config = RtcEngineConfig().apply {
                        mContext = applicationContext
                        mAppId = "Your App ID"
                        mChannelProfile = Constants.CHANNEL_PROFILE_LIVE_BROADCASTING
                        mEventHandler = mRtcEventHandler // You'll need to define this
                    }

                    mRtcEngine = RtcEngine.create(config)
                } catch (e: Exception) {
                    throw RuntimeException("Error initializing RTC engine: ${e.message}")
                }
            }
        }
        ```

        ### Enable accelerated rendering [#enable-accelerated-rendering]

        Call [`enableInstantMediaRendering`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_irtcengine.html#api_irtcengine_enableinstantmediarendering) to reduce the time it takes to render the first video frame and play audio after joining a channel.

        * Call this method **before** joining a channel. Ideally, call it right after engine initialization.
        * Both host and audience must call this method to benefit from faster rendering.
        * To disable this feature, destroy the engine with `release`, then reinitialize it.

        ```kotlin
        // Enable accelerated rendering before joining the channel
        mRtcEngine?.enableInstantMediaRendering()
        ```

        ### Set a video scenario [#set-a-video-scenario]

        Use [`setVideoScenario`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_irtcengine.html#api_irtcengine_setvideoscenario) to optimize performance for your specific use case. The SDK applies strategies tailored to the selected scenario.

        For example, for a one-on-one call, use `APPLICATION_SCENARIO_1V1`.

        ```kotlin
        // Set the video scenario
        mRtcEngine?.setVideoScenario(Constants.APPLICATION_SCENARIO_1V1)
        ```

        ### Preload a channel [#preload-a-channel]

        Joining a channel involves acquiring server resources and establishing a connection. Call [`preloadChannel`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_irtcengine.html#api_irtcengine_preloadchannel) to handle resource acquisition early and reduce join time.

        * The `token`, `channelId`, and `uid` must match the values used in `joinChannel`.
        * Call `preloadChannel` as soon as you retrieve the required info.
        * Don’t call `joinChannel` immediately after `preloadChannel`.

        ```kotlin
        private fun prepareChannelInfo(): Int {
            uid = getUid()
            channelId = getChannelInfo()
            token = getTokenFromServer(channelId, uid)

            // Preload the channel
            mRtcEngine?.preloadChannel(token, channelId, uid)

            return 0 // Return success code, adjust as needed
        }
        ```

        ### Set up the rendering view [#set-up-the-rendering-view]

        Setting the rendering view early ensures the first frame displays properly. If the view is not ready, the first frame might be skipped.

        If your app knows the remote user ID (For example, from Signaling), set the view immediately. Otherwise, use the `onUserJoined` callback.

        * **Set the remote view early:**

        ```kotlin
        fun onShowChannels(channelId: String, remoteUid: Int) {
            val canvas = VideoCanvas(null, VideoCanvas.RENDER_MODE_FIT, remoteUid)
            mRtcEngine?.setupRemoteVideo(canvas)
        }

        fun onEIDUserJoined(uid: Int, elapsed: Int) {
            // Already set - no additional setup needed
        }
        ```

        * **Set the view when the user joins:**

        ```kotlin
        // Event handler class
        private val mRtcEventHandler = object : IRtcEngineEventHandler() {
            override fun onUserJoined(uid: Int, elapsed: Int) {
                // Forward to UI logic
                runOnUiThread {
                    onEIDUserJoined(uid, elapsed)
                }
            }
        }

        fun onEIDUserJoined(uid: Int, elapsed: Int) {
            val canvas = VideoCanvas(surfaceView, VideoCanvas.RENDER_MODE_FIT, uid)
            mRtcEngine?.setupRemoteVideo(canvas)
        }
        ```

        ### Monitor rendering performance [#monitor-rendering-performance]

        Use [`startMediaRenderingTracing`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_irtcengine.html#api_irtcengine_startmediarenderingtracing) to monitor first-frame rendering metrics. Results are reported via [`onVideoRenderingTracingResult`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_irtcengineeventhandler.html#callback_irtcengineeventhandler_onvideorenderingtracingresult).

        <CalloutContainer type="info">
          <CalloutDescription>
            Call this method when the user initiates joining. For example, on a **Join** button tap. This gives accurate first-frame timing.
          </CalloutDescription>
        </CalloutContainer>

        ```kotlin
        private fun onJoinClicked() {
            mRtcEngine?.startMediaRenderingTracing()
            mRtcEngine?.joinChannel(token, channelId, uid, options)
        }
        ```

        ### Join a channel [#join-a-channel]

        Call [`joinChannel`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_irtcengine.html#api_irtcengine_joinchannel2) to enter the channel. To speed up first-frame playback, avoid delays like fetching a token in this method.

        If you can’t retrieve a token early, consider using a [wildcard token](/en/realtime-media/interactive-live-streaming/build/authenticate-users/deploy-token-server#generate-wildcard-tokens).

        ```kotlin
        private fun prepareChannelInfo(): Int {
            uid = getUid()
            channelId = getChannelInfo()
            token = getTokenFromServer(channelId, uid)
            return 0 // Return success code
        }

        private fun joinChannel(): Int {
            val options = ChannelMediaOptions()
            return mRtcEngine?.joinChannel(token, channelId, uid, options) ?: -1
        }
        ```

        ### Optimize callback performance [#optimize-callback-performance]

        The SDK runs callbacks like `onJoinChannelSuccess` on the same thread. If one callback is slow, it can delay others—including rendering events.

        <CalloutContainer type="info">
          <CalloutDescription>
            Don’t block the callback thread with network calls, file I/O, or heavy processing.
          </CalloutDescription>
        </CalloutContainer>

        #### Best practices [#best-practices]

        * Avoid complex operations in `onJoinChannelSuccess`.
        * Don’t block `onUserJoined` or other rendering-related callbacks.
        * Use background threads for heavy logic.
      </TabsContent>

      <TabsContent value="subscribe">
        The following figure illustrates the essential steps:

        ### Sequence diagram for implementation [#sequence-diagram-for-implementation-1]

        ![Sequence diagram for optimized video rendering](https://assets-docs.agora.io/images/video-sdk/optimize-video-rendering-solution-2.svg)

        ### Set up the rendering view [#set-up-the-rendering-view-1]

        If you know the host’s user ID before joining the channel, call [`setupRemoteVideoEx`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_irtcengineex.html#api_irtcengineex_setupremotevideoex) as early as possible to set up the rendering view. This ensures the rendering pipeline is initialized in advance, helping avoid delays in displaying the first decoded frame.

        If the host’s user ID is not available beforehand, wait for the `onUserJoined` callback, then call [`setupRemoteVideoEx`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_irtcengineex.html#api_irtcengineex_setupremotevideoex).

        ```kotlin
        val canvas = VideoCanvas(getView(), VideoCanvas.RENDER_MODE_FIT, farNextChannel.remoteUid)
        mRtcEngine?.setupRemoteVideoEx(canvas, connection)
        ```

        ### Join a channel without automatically subscribing [#join-a-channel-without-automatically-subscribing]

        Joining a channel typically takes the most time before the first video frame appears. For use cases like fast channel switching, delay subscribing to media streams to speed up rendering:

        1. Call [`joinChannelEx`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_irtcengineex.html#api_irtcengineex_joinchannelex) to join the channel.
        2. In [`ChannelMediaOptions`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_channelmediaoptions.html), set `autoSubscribeAudio` and `autoSubscribeVideo` to `false`.
        3. Subscribe manually when the user is ready to view content.

           ```kotlin
           // Define connection and event handler
           val connection = RtcConnection(channelId, uid)
           val eventHandler = mRtcEventHandler

           // Set channel media options
           val options = ChannelMediaOptions().apply {
               channelProfile = Constants.CHANNEL_PROFILE_LIVE_BROADCASTING
               clientRoleType = Constants.CLIENT_ROLE_AUDIENCE
               autoSubscribeAudio = false
               autoSubscribeVideo = false
           }

           // Join the channel without subscribing
           mRtcEngine?.joinChannelEx(token, connection, options, mRtcEventHandler)
           ```

        ### Subscribe to streams and start rendering [#subscribe-to-streams-and-start-rendering]

        When the user chooses to view content:

        1. Resume media subscription using [`muteRemoteVideoStreamEx`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_irtcengineex.html#api_irtcengineex_muteremotevideostreamex) and [`muteRemoteAudioStreamEx`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_irtcengineex.html#api_irtcengineex_muteremoteaudiostreamex).
        2. Call [`startMediaRenderingTracingEx`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_irtcengineex.html#api_irtcengineex_startmediarenderingtracingex) to log rendering metrics.
        3. The SDK reports results in the [`onVideoRenderingTracingResult`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_irtcengineeventhandler.html#callback_irtcengineeventhandler_onvideorenderingtracingresult) callback, which you can use for performance analysis.

           ```kotlin
           fun switchToChannel() {
               // Start video rendering tracing
               mRtcEngine?.startMediaRenderingTracingEx(connection)

               // Resume remote media subscriptions
               mRtcEngine?.muteRemoteVideoStreamEx(remoteUid, false, connection)
               mRtcEngine?.muteRemoteAudioStreamEx(remoteUid, false, connection)
           }
           ```
      </TabsContent>
    </Tabs>

    ## Troubleshooting [#troubleshooting]

    Refer to [Slow first-frame rendering of remote video when using the Agora Video SDK](/en/api-reference/faq/quality/optimize_video_rendering).