# Alpha transparency effect (/en/realtime-media/interactive-live-streaming/build/apply-effects-and-enhancements/alpha-transparency-effect)

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

In various real-time video interaction use-cases, segmenting the host's background and applying transparent special effects can make the interaction more engaging, enhance immersion, and improve the overall interactive experience.


      
Consider the following sample use-cases:

* **Broadcaster background replacement**: The audience sees the broadcaster's background in the video replaced with a virtual scene, such as a gaming environment, a conference, or a tourist attractions.

* **Animated virtual gifts**: Display dynamic animations with a transparent background to avoid obscuring live content when multiple video streams are merged.

* **Chroma keying during live game streaming**: The audience sees the broadcaster's image cropped and positioned within the local game screen, making it appear as though the broadcaster is part of the game.

![image](https://assets-docs.agora.io/images/video-sdk/alpha-transparency-demo.png)

## Prerequisites

Ensure that you have implemented the [SDK quickstart](../../index.mdx) in your project.

## Implement alpha transparency

Choose one of the following methods to implement the Alpha transparency effect based on your specific business use-case.

### Custom video capture use-case

The implementation process for this use-case is illustrated in the figure below:

**Alpha transparency custom video capture use-case**

![Custom Video Capture Process 1](https://assets-docs.agora.io/images/video-sdk/alpha-transparency-scenario-1.svg)

Take the following steps to implement this logic:

1. Process the captured video frames and generate Alpha data. You can choose from the following methods:

   * **Method 1**: Call the `pushExternalVideoFrame`\[2/2] method and set the `alphaBuffer` parameter to specify Alpha channel data for the video frames. This data matches the size of the video frames, with each pixel value ranging from 0 to 255, where 0 represents the background and 255 represents the foreground.

     <CalloutContainer type="warning">
       <CalloutDescription>
         Ensure that `alphaBuffer` is exactly the same size as the video frame (width × height), otherwise the app may crash.
       </CalloutDescription>
     </CalloutContainer>

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    ```java
    JavaI420Buffer javaI420Buffer = JavaI420Buffer.wrap(width, height, dataY, width, dataU, strideUV, dataV, strideUV, null);
       VideoFrame frame = new VideoFrame(javaI420Buffer, 0, timestamp);
       ByteBuffer alphaBuffer = ByteBuffer.allocateDirect(width * height);
       frame.fillAlphaData(alphaBuffer);
       rtcEngine.pushExternalVideoFrame(frame);
    ```
  </CodeBlockTab>

  <CodeBlockTab value="kotlin">
    ```kotlin
    val javaI420Buffer = JavaI420Buffer.wrap(width, height, dataY, width, dataU, strideUV, dataV, strideUV, null)
       val frame = VideoFrame(javaI420Buffer, 0, timestamp)
       val alphaBuffer = ByteBuffer.allocateDirect(width * height)
       frame.fillAlphaData(alphaBuffer)
       rtcEngine.pushExternalVideoFrame(frame)
    ```
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* **Method 2**: Call the `pushExternalVideoFrame` method and use the `setAlphaStitchMode` method in the `VideoFrame` class to set the Alpha stitching mode. Construct a `VideoFrame` with the stitched Alpha data.

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    ```java
    JavaI420Buffer javaI420Buffer = JavaI420Buffer.wrap(width, height, dataY, width, dataU, strideUV, dataV, strideUV, null);
       VideoFrame frame = new VideoFrame(javaI420Buffer, 0, timestamp);
       // Set the Alpha stitching mode, in the example below, Alpha is set to be below the video image
       frame.setAlphaStitchMode(Constants.VIDEO_ALPHA_STITCH_BELOW);
       rtcEngine.pushExternalVideoFrame(frame);
    ```
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    ```kotlin
    val javaI420Buffer = JavaI420Buffer.wrap(width, height, dataY, width, dataU, strideUV, dataV, strideUV, null)
       val frame = VideoFrame(javaI420Buffer, 0, timestamp)
       // Set the Alpha stitching mode, in the example below, Alpha is set to be below the video image
       frame.setAlphaStitchMode(Constants.VIDEO_ALPHA_STITCH_BELOW)
       rtcEngine.pushExternalVideoFrame(frame)
    ```
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2. Render the local view and implement the Alpha transparency effect.

   * Create a `TextureView` object for rendering the local view.
   * Call the `setupLocalVideo` method to set the local view:
   * Set the `enableAlphaMask` parameter to `true` to enable alpha mask rendering.
   * Set `TextureView` as the display window for the local video.

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    ```java
    // Alpha data input on the sender side and Alpha transmission is enabled
        VideoEncoderConfiguration config = new VideoEncoderConfiguration(...);
        // Alpha transfer needs to be enabled when setting encoding parameters.
        config.advanceOptions.encodeAlpha = true;
        rtcEngine.setVideoEncoderConfiguration(videoEncoderConfiguration);

        // Set the view to TextureView
        TextureView textureView = new TextureView(context);
        // Enable transparent mode, allowing transparent portions in the view background and content
        textureView.setOpaque(false);
        fl_local.addView(textureView, new FrameLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT));

        VideoCanvas local = new VideoCanvas(textureView, RENDER_MODE_FIT, 0);
        local.enableAlphaMask = true;
        rtcEngine.setupLocalVideo(local);
    ```
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    ```kotlin
    // Alpha data input on the sender side and Alpha transmission is enabled
        val config = VideoEncoderConfiguration(...)
        // Alpha transfer needs to be enabled when setting encoding parameters.
        config.advanceOptions.encodeAlpha = true
        rtcEngine.setVideoEncoderConfiguration(videoEncoderConfiguration)

        // Set the view to TextureView
        val textureView = TextureView(context)
        // Enable transparent mode, allowing transparent portions in the view background and content
        textureView.isOpaque = false
        fl_local.addView(textureView, FrameLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT))

        val local = VideoCanvas(textureView, RENDER_MODE_FIT, 0)
        local.enableAlphaMask = true
        rtcEngine.setupLocalVideo(local)
    ```
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3. Render the local view of the remote video stream and implement alpha transparency effects.
   * After receiving the `onUserJoined` callback, a `TextureView` object is created for rendering the remote view.
   * Call the `setupRemoteVideo` method to set the remote view:
   * Set the `enableAlphaMask` parameter to true to enable alpha mask rendering.
   * Set the display window of the remote video stream in the local video.

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    ```java
    // Enable transparent mode at the receiving end
        TextureView textureView = new TextureView(context);
        textureView.setOpaque(false);
        fl_remote.addView(textureView, new FrameLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT));

        VideoCanvas remote = new VideoCanvas(textureView, VideoCanvas.RENDER_MODE_FIT, uid);
        remote.enableAlphaMask = true;
        rtcEngine.setupRemoteVideo(remote);
    ```
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    ```kotlin
    // Enable transparent mode at the receiving end
        val textureView = TextureView(context)
        textureView.isOpaque = false
        fl_remote.addView(textureView, FrameLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT))

        val remote = VideoCanvas(textureView, VideoCanvas.RENDER_MODE_FIT, uid)
        remote.enableAlphaMask = true
        rtcEngine.setupRemoteVideo(remote)
    ```
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### SDK Capture use-case

The implementation process for this use-case is illustrated in the following figure:

**Alpha transparency SDK capture use-case**

![Custom Video Capture Process 2](https://assets-docs.agora.io/images/video-sdk/alpha-transparency-scenario-2.svg)

Take the following steps to implement this logic:

1. On the broadcasting end, call the `enableVirtualBackground` \[2/2] method to enable the background segmentation algorithm and obtain the Alpha data for the portrait area. Set the parameters as follows:

   * `enabled`: Set to `true` to enable the virtual background.
   * `backgroundSourceType`: Set to `BACKGROUND_NONE`(0), to segment the portrait and background, and process the background as Alpha data.

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    ```java
    VirtualBackgroundSource virtualBackgroundSource = new VirtualBackgroundSource(...);
       virtualBackgroundSource.backgroundSourceType = VirtualBackgroundSource.BACKGROUND_NONE; // Only generate alpha data, no background replacement
       SegmentationProperty segmentationProperty = new SegmentationProperty(...);
       rtcEngine.enableVirtualBackground(true, virtualBackgroundSource, segmentationProperty, sourceType);
    ```
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    ```kotlin
    val virtualBackgroundSource = VirtualBackgroundSource(...)
       virtualBackgroundSource.backgroundSourceType = VirtualBackgroundSource.BACKGROUND_NONE // Only generate alpha data, no background replacement
       val segmentationProperty = SegmentationProperty(...)
       rtcEngine.enableVirtualBackground(true, virtualBackgroundSource, segmentationProperty, sourceType)
    ```
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2. Call `setVideoEncoderConfiguration` on the broadcasting end to set the video encoding property and set `encodeAlpha` to `true`. Then the Alpha data will be encoded and sent to the remote end.

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    ```java
    VideoEncoderConfiguration videoEncoderConfiguration = new VideoEncoderConfiguration(...);
      videoEncoderConfiguration.advanceOptions = new VideoEncoderConfiguration.AdvanceOptions(...);
      videoEncoderConfiguration.advanceOptions.encodeAlpha = true;
      rtcEngine.setVideoEncoderConfiguration(videoEncoderConfiguration);
    ```
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    ```kotlin
    val videoEncoderConfiguration = VideoEncoderConfiguration(...)
      videoEncoderConfiguration.advanceOptions = VideoEncoderConfiguration.AdvanceOptions(...)
      videoEncoderConfiguration.advanceOptions.encodeAlpha = true
      rtcEngine.setVideoEncoderConfiguration(videoEncoderConfiguration)
    ```
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3. Render the local and remote views and implement the Alpha transparency effect. See the steps in the [Custom Video Capture use-case](#custom-video-capture-use-case) for details.

### Raw video data use-case

The implementation process for this use-case is illustrated in the following figure:

**Alpha transparency raw video data use-case**

![Custom Video Capture Process 3](https://assets-docs.agora.io/images/video-sdk/alpha-transparency-scenario-3.svg)

Take the following steps to implement this logic:

1. Call the `registerVideoFrameObserver` method to register a raw video frame observer and implement the corresponding callbacks as required.

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    ```java
    // Register IVideoFrameObserver
      public class MyVideoFrameObserver implements IVideoFrameObserver {
        @Override
        public boolean onRenderVideoFrame(String channelId, int uId, VideoFrame videoFrame) {
          // ...
          return false;
        }

        @Override
        public boolean onCaptureVideoFrame(int type, VideoFrame videoFrame) {
          // ...
          return false;
        }

        @Override
        public boolean onPreEncodeVideoFrame(int type, VideoFrame videoFrame) {
          // ...
          return false;
        }
      }
      MyVideoFrameObserver observer = new MyVideoFrameObserver();
      rtcEngine.registerVideoFrameObserver(observer);
    ```
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    ```kotlin
    // Register IVideoFrameObserver
      class MyVideoFrameObserver : IVideoFrameObserver {
        override fun onRenderVideoFrame(channelId: String, uId: Int, videoFrame: VideoFrame): Boolean {
          // ...
          return false
        }

        override fun onCaptureVideoFrame(type: Int, videoFrame: VideoFrame): Boolean {
          // ...
          return false
        }

        override fun onPreEncodeVideoFrame(type: Int, videoFrame: VideoFrame): Boolean {
          // ...
          return false
        }
      }
      val observer = MyVideoFrameObserver()
      rtcEngine.registerVideoFrameObserver(observer)
    ```
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2. Use the `onCaptureVideoFrame` callback to obtain the captured video data and pre-process it as needed. You can modify the Alpha data or directly add Alpha data.

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    ```java
    public boolean onCaptureVideoFrame(int type, VideoFrame videoFrame) {
        // Modify Alpha data or directly add Alpha data
        ByteBuffer alphaBuffer = videoFrame.getAlphaBuffer();
        // ...
        videoFrame.fillAlphaData(byteBuffer);
        return false;
      }
    ```
  </CodeBlockTab>

  <CodeBlockTab value="kotlin">
    ```kotlin
    override fun onCaptureVideoFrame(type: Int, videoFrame: VideoFrame): Boolean {
        // Modify Alpha data or directly add Alpha data
        val alphaBuffer = videoFrame.alphaBuffer
        // ...
        videoFrame.fillAlphaData(byteBuffer)
        return false
      }
    ```
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3. Use the `onPreEncodeVideoFrame` callback to obtain the local video data before encoding, and modify or directly add Alpha data as needed.

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    ```java
    public boolean onPreEncodeVideoFrame(int type, VideoFrame videoFrame) {
        // Modify Alpha data or directly add Alpha data
        ByteBuffer alphaBuffer = videoFrame.getAlphaBuffer();
        // ...
        videoFrame.fillAlphaData(byteBuffer);
        return false;
      }
    ```
  </CodeBlockTab>

  <CodeBlockTab value="kotlin">
    ```kotlin
    override fun onPreEncodeVideoFrame(type: Int, videoFrame: VideoFrame): Boolean {
        // Modify Alpha data or directly add Alpha data
        val alphaBuffer = videoFrame.alphaBuffer
        // ...
        videoFrame.fillAlphaData(byteBuffer)
        return false
      }
    ```
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4. Use the `onRenderVideoFrame` callback to obtain the remote video data before rendering it locally. Modify the Alpha data, add Alpha data directly, or render the video image yourself based on the obtained Alpha data.

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    ```java
    public boolean onRenderVideoFrame(int type, VideoFrame videoFrame) {
        // Modify Alpha data, directly add Alpha data, or render the video image yourself based on the obtained Alpha data
        ByteBuffer alphaBuffer = videoFrame.getAlphaBuffer();
        // ...
        videoFrame.fillAlphaData(byteBuffer);
        return false;
      }
    ```
  </CodeBlockTab>

  <CodeBlockTab value="kotlin">
    ```kotlin
    override fun onRenderVideoFrame(type: Int, videoFrame: VideoFrame): Boolean {
        // Modify Alpha data, directly add Alpha data, or render the video image yourself based on the obtained Alpha data
        val alphaBuffer = videoFrame.alphaBuffer
        // ...
        videoFrame.fillAlphaData(byteBuffer)
        return false
      }
    ```
  </CodeBlockTab>
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### Development notes

* Implement the transparency properties of the app window yourself and handle the transparency relationship when multiple windows are stacked on top of each other (achieved by adjusting the `zOrder` of the window).

* On Android, only `TextureView` and `SurfaceView` are supported when setting the view due to system limitations.

## Reference

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

### API reference

* [`VideoFrame`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_videoframe.html)
* [`pushExternalVideoFrame` \[2/2\]](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_irtcengine.html#api_irtcengine_pushvideoframe4)
* [`setupLocalVideo`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_irtcengine.html#api_irtcengine_setuplocalvideo)
* [`setupRemoteVideo`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_irtcengine.html#api_irtcengine_setupremotevideo)
* [`enableVirtualBackground`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_irtcengine.html#api_irtcengine_enablevirtualbackground2)
* [`registerVideoFrameObserver`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_irtcengine.html#api_imediaengine_registervideoframeobserver)
* [`onCaptureVideoFrame`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_ivideoframeobserver.html#callback_ivideoframeobserver_oncapturevideoframe)
* [`onPreEncodeVideoFrame`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_ivideoframeobserver.html#callback_ivideoframeobserver_onpreencodevideoframe)
* [`onRenderVideoFrame`](https://api-ref.agora.io/en/video-sdk/android/4.x/API/class_ivideoframeobserver.html#callback_ivideoframeobserver_onrendervideoframe)

    
  
      
  
      
  
      
  
      
  
      
  


## Platform-specific versions
- [Android](/en/realtime-media/interactive-live-streaming/build/apply-effects-and-enhancements/alpha-transparency-effect/android.md)
- [iOS](/en/realtime-media/interactive-live-streaming/build/apply-effects-and-enhancements/alpha-transparency-effect/ios.md)
- [macOS](/en/realtime-media/interactive-live-streaming/build/apply-effects-and-enhancements/alpha-transparency-effect/macos.md)
- [Windows](/en/realtime-media/interactive-live-streaming/build/apply-effects-and-enhancements/alpha-transparency-effect/windows.md)
- [React Native](/en/realtime-media/interactive-live-streaming/build/apply-effects-and-enhancements/alpha-transparency-effect/react-native.md)
- [Unity](/en/realtime-media/interactive-live-streaming/build/apply-effects-and-enhancements/alpha-transparency-effect/unity.md)