Alpha transparency effect

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.

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 use-case.

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

Alpha transparency custom video capture use-case

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.

     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);

     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)

   • 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.

     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 imageframe.setAlphaStitchMode(Constants.VIDEO_ALPHA_STITCH_BELOW);rtcEngine.pushExternalVideoFrame(frame);

     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 imageframe.setAlphaStitchMode(Constants.VIDEO_ALPHA_STITCH_BELOW)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.

       Java

       // Alpha data input on the sender side and Alpha transmission is enabledVideoEncoderConfiguration config = new VideoEncoderConfiguration(...);// Alpha transfer needs to be enabled when setting encoding parameters.config.advanceOptions.encodeAlpha = true;rtcEngine.setVideoEncoderConfiguration(videoEncoderConfiguration);// Set the view to TextureViewTextureView textureView = new TextureView(context);// Enable transparent mode, allowing transparent portions in the view background and contenttextureView.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);

       Kotlin

       // Alpha data input on the sender side and Alpha transmission is enabledval config = VideoEncoderConfiguration(...)// Alpha transfer needs to be enabled when setting encoding parameters.config.advanceOptions.encodeAlpha = truertcEngine.setVideoEncoderConfiguration(videoEncoderConfiguration)// Set the view to TextureViewval textureView = TextureView(context)// Enable transparent mode, allowing transparent portions in the view background and contenttextureView.isOpaque = falsefl_local.addView(textureView, FrameLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT))val local = VideoCanvas(textureView, RENDER_MODE_FIT, 0)local.enableAlphaMask = truertcEngine.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.

       Java

       // Enable transparent mode at the receiving endTextureView 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);

       Kotlin

       // Enable transparent mode at the receiving endval textureView = TextureView(context)textureView.isOpaque = falsefl_remote.addView(textureView, FrameLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT))val remote = VideoCanvas(textureView, VideoCanvas.RENDER_MODE_FIT, uid)remote.enableAlphaMask = truertcEngine.setupRemoteVideo(remote)

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

Alpha transparency SDK capture use-case

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.

     Java

     VirtualBackgroundSource virtualBackgroundSource = new VirtualBackgroundSource(...);virtualBackgroundSource.backgroundSourceType = VirtualBackgroundSource.BACKGROUND_NONE; // Only generate alpha data, no background replacementSegmentationProperty segmentationProperty = new SegmentationProperty(...);rtcEngine.enableVirtualBackground(true, virtualBackgroundSource, segmentationProperty, sourceType);

     Kotlin

     val virtualBackgroundSource = VirtualBackgroundSource(...)virtualBackgroundSource.backgroundSourceType = VirtualBackgroundSource.BACKGROUND_NONE // Only generate alpha data, no background replacementval segmentationProperty = SegmentationProperty(...)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.

   Java

   VideoEncoderConfiguration videoEncoderConfiguration = new VideoEncoderConfiguration(...);videoEncoderConfiguration.advanceOptions = new VideoEncoderConfiguration.AdvanceOptions(...);videoEncoderConfiguration.advanceOptions.encodeAlpha = true;rtcEngine.setVideoEncoderConfiguration(videoEncoderConfiguration);

   Kotlin

   val videoEncoderConfiguration = VideoEncoderConfiguration(...)videoEncoderConfiguration.advanceOptions = VideoEncoderConfiguration.AdvanceOptions(...)videoEncoderConfiguration.advanceOptions.encodeAlpha = truertcEngine.setVideoEncoderConfiguration(videoEncoderConfiguration)

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

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

Alpha transparency raw video data use-case

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.

   Java

   // Register IVideoFrameObserverpublic 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);

   Kotlin

   // Register IVideoFrameObserverclass 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)

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.

   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;}

   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}

3. Use the onPreEncodeVideoFrame callback to obtain the local video data before encoding, and modify or directly add Alpha data as needed.

   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;}

   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}

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.

   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;}

   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}

• 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