如何使用AVAssetReader和AVAssetWriter裁剪视频

import AVFoundation

func trimVideo(inputURL: URL, outputURL: URL, startTime: CMTime, endTime: CMTime, completion: @escaping (Error?) -> Void) {
    let asset = AVAsset(url: inputURL)
    
    guard let reader = try? AVAssetReader(asset: asset) else {
        completion(NSError(domain: "com.example", code: 0, userInfo: [NSLocalizedDescriptionKey: "Failed to create AVAssetReader"]))
        return
    }
    
    guard let videoTrack = asset.tracks(withMediaType: .video).first else {
        completion(NSError(domain: "com.example", code: 0, userInfo: [NSLocalizedDescriptionKey: "Video track not found"]))
        return
    }
    
    let readerOutput = AVAssetReaderTrackOutput(track: videoTrack, outputSettings: nil)
    reader.add(readerOutput)
    
    guard reader.startReading() else {
        completion(NSError(domain: "com.example", code: 0, userInfo: [NSLocalizedDescriptionKey: "Failed to start AVAssetReader"]))
        return
    }
    
    guard let writer = try? AVAssetWriter(outputURL: outputURL, fileType: .mp4) else {
        completion(NSError(domain: "com.example", code: 0, userInfo: [NSLocalizedDescriptionKey: "Failed to create AVAssetWriter"]))
        return
    }
    
    let writerInput = AVAssetWriterInput(mediaType: .video, outputSettings: nil)
    writer.add(writerInput)
    
    writer.startWriting()
    writer.startSession(atSourceTime: startTime)
    
    let mediaInputQueue = DispatchQueue(label: "mediaInputQueue")
    writerInput.requestMediaDataWhenReady(on: mediaInputQueue) {
        while writerInput.isReadyForMoreMediaData {
            guard let sampleBuffer = readerOutput.copyNextSampleBuffer() else {
                writerInput.markAsFinished()
                writer.finishWriting(completionHandler: {
                    completion(writer.error)
                })
                return
            }
            
            let presentationTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer)
            if presentationTime >= endTime {
                writerInput.markAsFinished()
                writer.finishWriting(completionHandler: {
                    completion(writer.error)
                })
                return
            }
            
            writerInput.append(sampleBuffer)
        }
    }
}