Alpha transparency effect

In various real-time audio and video interaction scenarios, 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 scenarios:

• 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.

Ensure that you have implemented the SDK quickstart in your project.

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

The implementation process for this scenario is illustrated in the figure below:

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.
   caution

   Ensure that alphaBuffer is exactly the same size as the video frame (width × height), otherwise the app may crash.

   
   

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   JavaI420Buffer javaI420Buffer = JavaI420Buffer.wrap(width, height, dataY, width, dataU, strideUV, dataV, strideUV, null);

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   VideoFrame frame = new VideoFrame(javaI420Buffer, 0, timestamp);

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   ByteBuffer alphaBuffer = ByteBuffer.allocateDirect(width * height);

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   frame.fillAlphaData(alphaBuffer);

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   rtcEngine.pushExternalVideoFrame(frame);

   
   

   • 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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     JavaI420Buffer javaI420Buffer = JavaI420Buffer.wrap(width, height, dataY, width, dataU, strideUV, dataV, strideUV, null);

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     VideoFrame frame = new VideoFrame(javaI420Buffer, 0, timestamp);

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     // Set the Alpha stitching mode, in the example below, Alpha is set to be below the video image

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     frame.setAlphaStitchMode(Constants.VIDEO_ALPHA_STITCH_BELOW);

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     rtcEngine.pushExternalVideoFrame(frame);

     
     

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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       // Alpha data input on the sender side and Alpha transmission is enabled

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       VideoEncoderConfiguration config = new VideoEncoderConfiguration(...);

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       // Alpha transfer needs to be enabled when setting encoding parameters.

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       config.advanceOptions.encodeAlpha = true;

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       rtcEngine.setVideoEncoderConfiguration(videoEncoderConfiguration);

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       // Set the view to TextureView

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       TextureView textureView = new TextureView(context);

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       // Enable transparent mode, allowing transparent portions in the view background and content

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       textureView.setOpaque(false);

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       fl_local.addView(textureView, new FrameLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT));

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       VideoCanvas local = new VideoCanvas(textureView, RENDER_MODE_FIT, 0);

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       local.enableAlphaMask = true;

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       rtcEngine.setupLocalVideo(local);

       
       

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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     // Enable transparent mode at the receiving end

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     TextureView textureView = new TextureView(context);

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     textureView.setOpaque(false);

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     fl_remote.addView(textureView, new FrameLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT));

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     VideoCanvas remote = new VideoCanvas(textureView, VideoCanvas.RENDER_MODE_FIT, uid);

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     remote.enableAlphaMask = true;

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     rtcEngine.setupRemoteVideo(remote);

     
     

The implementation process for this scenario is illustrated in the following figure:

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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   VirtualBackgroundSource virtualBackgroundSource = new VirtualBackgroundSource(...);

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   virtualBackgroundSource.backgroundSourceType = VirtualBackgroundSource.BACKGROUND_NONE; // Only generate alpha data, no background replacement

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   SegmentationProperty segmentationProperty = new SegmentationProperty(...);

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   rtcEngine.enableVirtualBackground(true, virtualBackgroundSource, segmentationProperty, sourceType);

   
   

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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   VideoEncoderConfiguration videoEncoderConfiguration = new VideoEncoderConfiguration(...);

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   videoEncoderConfiguration.advanceOptions = new VideoEncoderConfiguration.AdvanceOptions(...);

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   videoEncoderConfiguration.advanceOptions.encodeAlpha = true;

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   rtcEngine.setVideoEncoderConfiguration(videoEncoderConfiguration);

   
   

3. Render the local and remote views and implement the Alpha transparency effect. See the steps in the Custom Video Capture Scenario for details.

The implementation process for this scenario is illustrated in the following figure:

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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   // Register IVideoFrameObserver

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   public class MyVideoFrameObserver implements IVideoFrameObserver {

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   @Override

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   public boolean onRenderVideoFrame(String channelId, int uId, VideoFrame videoFrame) {

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   // ...

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   return false;

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   }

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   @Override

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   public boolean onCaptureVideoFrame(int type, VideoFrame videoFrame) {

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   // ...

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   return false;

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   }

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   @Override

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   public boolean onPreEncodeVideoFrame(int type, VideoFrame videoFrame) {

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   // ...

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   return false;

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   }

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   }

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   MyVideoFrameObserver observer = new MyVideoFrameObserver();

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   rtcEngine.registerVideoFrameObserver(observer);

   
   

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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   public boolean onCaptureVideoFrame(int type, VideoFrame videoFrame) {

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   // Modify Alpha data or directly add Alpha data

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   ByteBuffer alphaBuffer = videoFrame.getAlphaBuffer();

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   // ...

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   videoFrame.fillAlphaData(byteBuffer);

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   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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   public boolean onPreEncodeVideoFrame(int type, VideoFrame videoFrame) {

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   // Modify Alpha data or directly add Alpha data

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   ByteBuffer alphaBuffer = videoFrame.getAlphaBuffer();

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   // ...

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   videoFrame.fillAlphaData(byteBuffer);

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   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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   public boolean onRenderVideoFrame(int type, VideoFrame videoFrame) {

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   // Modify Alpha data, directly add Alpha data, or render the video image yourself based on the obtained Alpha data

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   ByteBuffer alphaBuffer = videoFrame.getAlphaBuffer();

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   // ...

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   videoFrame.fillAlphaData(byteBuffer);

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   return false;

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   }

   
   

• 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.

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

• VideoFrame
• pushExternalVideoFrame [2/2]
• setupLocalVideo
• setupRemoteVideo
• enableVirtualBackground
• registerVideoFrameObserver
• onCaptureVideoFrame
• onPreEncodeVideoFrame
• onRenderVideoFrame