# Remove backgrounds with an alpha channel

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> The code on this page works with either the **default UI** or the **custom UI**.

Meeting hosts who hold a raw streaming token can enable alpha channel mode, which requests that Zoom send both
the original video data and a mask demarking the edge of a participant's body. The SDK can then use the alpha
mask and raw data to remove the participant's background and render meeting participants natively in the host's
virtual world.

## Add new methods

Add a new method to the `MobileRTCMeetingDelegate.h` class.

```objectivec
/*!
 @brief Callback event of alpha channel mode changes.
 @param alphaChannelOn YES means it's in alpha channel mode. Otherwise, it's not.
 */
- (void)onVideoAlphaChannelStatusChanged:(BOOL)alphaChannelOn;
```

This callback is triggered when alpha channel mode is turned on.

Add these methods to the `MobileRTCMeetingService+Video.h` class.

```objectivec
/*!
 @brief Determine if alpha channel mode can be enabled.
 @return YES means it can be enabled. Otherwise NO.  Only for host call.
 @warning Only host can enable alpha channel.
 */
- (BOOL)canEnableAlphaChannelMode;

/*!
 @brief Enable or disable alpha channel mode.
 @param enable YES indicates to enable alpha channel mode., Otherwise, disable it.
 @return If the function succeeds, the return value is MobileRTCSDKError_Success. Otherwise failed.
 @warning Only host can enable alpha channel.
 @warning  This function will enable the meeting alpha channel, even if the current iOS device not support alpha channel.
 @warning for iOS device should be iPhone 8/ 8 plus X or above or be iPad Pro 9.7 above, OS should be iOS 11 or above.
 */
- (MobileRTCSDKError)enableAlphaChannelMode:(BOOL)enable;

/*!
 @brief Determine if alpha channel mode is enabled.
 @return YES indicates is in alpha channel mode. Otherwise NO.
 */
- (BOOL)isAlphaChannelModeEnabled;
```

## Enable alpha channel mode

Before enabling the alpha channel, call `canEnableAlphaChannelMode` to check whether the alpha channel mode is enabled.
To enable or disable the alpha channel, call `EnableAlphaChannelMode`.

Add a new method to the class `MobileRTCVideoRawData.h`.

```objectivec
/*!
 @brief The data pointer to a video's alpha data.
 */
@property (nonatomic, assign) char *alphaBuffer;

/*!
 @brief the alpha buffer data length
 */
@property (nonatomic, assign) unsigned int alphaBufferLen;
```

The raw data will have two more values after performing these steps: `GetAlphaBuffer` for the alpha data buffer, and another, `GetAlphaBufferLen`, for the alpha data buffer length.

Now that you've received the data, [edit the raw data](/docs/meeting-sdk/ios/default-ui/advanced-features/raw-data).

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