How to convert RTCI420Buffer n Webrtc to CVPixelBuffer for iOS ？

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/// Convert RTCVideoFrame to CVPixelBuffer
func getCVPixelBuffer(frame: RTCVideoFrame?) -> CVPixelBuffer? {
    var buffer : RTCCVPixelBuffer?
    var pixelBuffer: CVPixelBuffer?
    
    if let inputBuffer = frame?.buffer {
        if let iBuffer = inputBuffer as? RTCI420Buffer {
            if let cvPixelBuffer = iBuffer.convertToCVPixelBuffer() {
                // Use the cvPixelBuffer as an RTCCVPixelBuffer
                // ...
                pixelBuffer = cvPixelBuffer
                return pixelBuffer
            }
            return pixelBuffer
        }
    }
    
    buffer = frame?.buffer as? RTCCVPixelBuffer
    pixelBuffer = buffer?.pixelBuffer
    return pixelBuffer
}

It is a question from text but not show about function of convertToCVPixelBuffer

So I don’t know how convertToCVPixelBuffer works ！