以下是一个示例代码，演示如何将CVPixelBuffer旋转一个视频：

import AVFoundation

func rotatePixelBuffer(_ pixelBuffer: CVPixelBuffer, rotationDegrees degrees: CGFloat) -> CVPixelBuffer? {
    let width = CVPixelBufferGetWidth(pixelBuffer)
    let height = CVPixelBufferGetHeight(pixelBuffer)
    let pixelFormat = CVPixelBufferGetPixelFormatType(pixelBuffer)
    
    var outputPixelBuffer: CVPixelBuffer?
    var status = CVPixelBufferCreate(nil, height, width, pixelFormat, nil, &outputPixelBuffer)
    guard status == kCVReturnSuccess, let unwrappedOutputPixelBuffer = outputPixelBuffer else {
        return nil
    }
    
    CVPixelBufferLockBaseAddress(pixelBuffer, .readOnly)
    CVPixelBufferLockBaseAddress(unwrappedOutputPixelBuffer, .writeOnly)
    
    let baseAddress = CVPixelBufferGetBaseAddress(pixelBuffer)
    let outputBaseAddress = CVPixelBufferGetBaseAddress(unwrappedOutputPixelBuffer)
    
    let bytesPerRow = CVPixelBufferGetBytesPerRow(pixelBuffer)
    let outputBytesPerRow = CVPixelBufferGetBytesPerRow(unwrappedOutputPixelBuffer)
    
    let srcBuffer = vImage_Buffer(data: baseAddress, height: vImagePixelCount(height), width: vImagePixelCount(width), rowBytes: bytesPerRow)
    var destBuffer = vImage_Buffer(data: outputBaseAddress, height: vImagePixelCount(width), width: vImagePixelCount(height), rowBytes: outputBytesPerRow)
    
    let rotation = degreesToRadians(degrees)
    let transform = CGAffineTransform(rotationAngle: rotation)
    
    status = vImageRotate90_ARGB8888(&srcBuffer, &destBuffer, UInt8(kRotateFlags), &transform, 0)
    if status != kvImageNoError {
        CVPixelBufferUnlockBaseAddress(pixelBuffer, .readOnly)
        CVPixelBufferUnlockBaseAddress(unwrappedOutputPixelBuffer, .writeOnly)
        return nil
    }
    
    CVPixelBufferUnlockBaseAddress(pixelBuffer, .readOnly)
    CVPixelBufferUnlockBaseAddress(unwrappedOutputPixelBuffer, .writeOnly)
    
    return unwrappedOutputPixelBuffer
}

func degreesToRadians(_ degrees: CGFloat) -> CGFloat {
    return degrees * .pi / 180
}

使用方法：

// 读取视频文件
guard let inputFile = Bundle.main.url(forResource: "inputVideo", withExtension: "mov") else {
    fatalError("Unable to locate input video file.")
}

// 创建AVAssetReader和AVAssetWriter
let asset = AVURLAsset(url: inputFile)
guard let reader = try? AVAssetReader(asset: asset), let writer = try? AVAssetWriter(outputURL: outputFile, fileType: .mov) else {
    fatalError("Unable to create AVAssetReader or AVAssetWriter.")
}

// 设置输入和输出
let videoTrack = asset.tracks(withMediaType: .video).first!
let outputSettings = [
    kCVPixelBufferPixelFormatTypeKey as String: Int(kCVPixelFormatType_32ARGB)
]
let readerOutput = AVAssetReaderTrackOutput(track: videoTrack, outputSettings: nil)
let writerOutput = AVAssetWriterInput(mediaType: .video, outputSettings: nil)
writerOutput.transform = videoTrack.preferredTransform
writerOutput.expectsMediaDataInRealTime = true

// 将CVPixelBuffer旋转
readerOutput.alwaysCopiesSampleData = false
readerOutput.setDelegate(self, queue: DispatchQueue(label: "com.example.video-processing"))

// 开始读取和写入
reader.add(readerOutput)
writer.add(writerOutput)
reader.startReading()
writer.startWriting()
writer.startSession(atSourceTime: CMTime.zero)

// 处理每个样本缓冲区
while let sampleBuffer = readerOutput.copyNextSampleBuffer() {
    if let pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer),
       let rotatedPixelBuffer = rotatePixelBuffer(pixelBuffer, rotationDegrees: 90) {
        writerInput.append(rotatedPixelBuffer, withPresentationTime: CMSampleBufferGetPresentationTimeStamp(sampleBuffer))
    }
    CMSampleBufferInvalidate(sampleBuffer)
}

// 完成读取和写入
reader.cancelReading()
writer.finishWriting {
    // 视频旋转完成
}

上述代码示例使用了vImageRotate90_ARGB8888函数将CVPixelBuffer旋转90度，你可以根据需要调整旋转角度。