# Raw video with alpha channel

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Session hosts who hold a raw streaming token can enable alpha channel mode, which requests that Zoom's Video SDK send both the original video data and an alpha mask marking the edge of a user's body. The Video SDK can then use the alpha mask and raw data to remove the user's background and render session users natively in the host's virtual world.

## Turn on alpha channel mode

Before turning on the alpha channel, call the following:

-   `canEnableAlphaChannelMode` to check whether the alpha channel mode can be enabled in the current session state.
-   `isDeviceSupportAlphaChannelMode` to check whether the device hardware is capable of supporting video alpha mode.

To turn the alpha channel on or off, call `enableAlphaChannelMode`.

```swift
if let videoHelper = ZoomVideoSDK.shareInstance()?.getVideoHelper(), videoHelper.canEnableAlphaChannelMode() {
    videoHelper.isDeviceSupportAlphaChannelMode() // Determines whether the device hardware is capable of supporting video alpha mode.
    videoHelper.enableAlphaChannelMode(true) // true/false to enable/disable alpha channel.
    videoHelper.isAlphaChannelModeEnabled()
}
```

```objectivec
ZoomVideoSDKVideoHelper *videoHelper = [[ZoomVideoSDK shareInstance] getVideoHelper];
if (videoHelper != nil) {
    if (videoHelper.canEnableAlphaChannelMode) {
        videoHelper.isDeviceSupportAlphaChannelMode; // Determines whether the device hardware is capable of supporting video alpha mode.
        [videoHelper enableAlphaChannelMode:TRUE]; // TRUE/FALSE to enable/disable alpha channel.
        videoHelper.isAlphaChannelModeEnabled;
    }
}
```

## Alpha channel callbacks

The `onVideoAlphaChannelStatusChanged` callback is triggered when alpha channel mode is turned on or off. After turning on the alpha channel, the raw video data includes two more values, `alphaBuffer` for the alpha data buffer and `alphaBufferLen` for the alpha data buffer length, in the same `onRawDataFrameReceived` callback.

Rely on `onVideoAlphaChannelStatusChanged` to know when alpha data is available, rather than null-checking `alphaBuffer` on every frame. Once you've received the data, edit the raw data to suit your use case. The alpha plane marks the user's silhouette against the Y, U, and V color planes, so read it alongside them when compositing.

```swift
func onVideoAlphaChannelStatusChanged(_ isAlphaChannelOn: Bool) {

}

func onRawDataFrameReceived(_ rawData: ZoomVideoSDKVideoRawData?) {
    guard let rawData = rawData else { return }
    // The Y, U, and V planes hold the color video.
    rawData.yBuffer
    rawData.uBuffer
    rawData.vBuffer
    // The alpha plane marks the edge of the user's body.
    rawData.alphaBuffer // Contains the buffer address only if alpha data exists. Otherwise null.
    rawData.alphaBufferLen
}
```

```objectivec
- (void)onVideoAlphaChannelStatusChanged:(BOOL)isAlphaChannelOn {

}

- (void)onRawDataFrameReceived:(ZoomVideoSDKVideoRawData *)rawData {
    if (!rawData) {
        return;
    }

    // The Y, U, and V planes hold the color video.
    rawData.yBuffer;
    rawData.uBuffer;
    rawData.vBuffer;
    // The alpha plane marks the edge of the user's body.
    rawData.alphaBuffer; // Contains the buffer address only if alpha data exists. Otherwise null.
    rawData.alphaBufferLen;
}
```