Dictionary Literal<_,_> 类型的值在强制转换中不符合 'Any'

Question

我正在尝试根据使用 Obj-C 的 SO post 在 swift 中设置自定义视频压缩 (How can I reduce the file size of a video created with UIImagePickerController?)。但是，我在转换语法时遇到了一些问题，特别是上面的错误在字典中突出显示。压缩函数如下：

func convertVideoToLowQuailty(withInputURL inputURL: URL, outputURL: URL) {
    //setup video writer
    var videoAsset = AVURLAsset(url: inputURL, options: nil)
    var videoTrack = videoAsset.tracks(withMediaType: AVMediaTypeVideo)[0]
    var videoSize = videoTrack.naturalSize
    var videoWriterCompressionSettings = [
        AVVideoAverageBitRateKey : Int(1250000)
    ]

    var videoWriterSettings : NSDictionary = [
        DictionaryLiteral : (Key: AVVideoCodecKey, Object: AVVideoCodecH264),
        AVVideoCompressionPropertiesKey : videoWriterCompressionSettings,
        AVVideoWidthKey : Int(videoSize.width),
        AVVideoHeightKey : Int(videoSize.height)
    ]

    var videoWriterInput = AVAssetWriterInput(mediaType: AVMediaTypeVideo, outputSettings: videoWriterSettings as! [String : Any?])
    videoWriterInput.expectsMediaDataInRealTime = true
    videoWriterInput.transform = videoTrack.preferredTransform
    var videoWriter = try! AVAssetWriter(outputURL: outputURL, fileType: AVFileTypeMPEG4)
    videoWriter.add(videoWriterInput)
    //setup video reader
    var videoReaderSettings = [ (kCVPixelBufferPixelFormatTypeKey as String) : Int(kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange) ]
    var videoReaderOutput = AVAssetReaderTrackOutput(track: videoTrack, outputSettings: videoReaderSettings)
    var videoReader = try! AVAssetReader(asset: videoAsset)
    videoReader.add(videoReaderOutput)
    //setup audio writer
    var audioWriterInput = AVAssetWriterInput(mediaType: AVMediaTypeAudio, outputSettings: nil)
    audioWriterInput.expectsMediaDataInRealTime = false
    videoWriter.add(audioWriterInput)
    //setup audio reader
    var audioTrack = videoAsset.tracks(withMediaType: AVMediaTypeAudio)[0]
    var audioReaderOutput = AVAssetReaderTrackOutput(track: audioTrack, outputSettings: nil)
    var audioReader = try! AVAssetReader(asset: videoAsset)
    audioReader.add(audioReaderOutput)
    videoWriter.startWriting()
    //start writing from video reader
    videoReader.startReading()
    videoWriter.startSession(atSourceTime: kCMTimeZero)
    var processingQueue = DispatchQueue(label: "processingQueue1")
    videoWriterInput.requestMediaDataWhenReady(on: processingQueue, using: {() -> Void in
        while videoWriterInput.isReadyForMoreMediaData {
            var sampleBuffer: CMSampleBuffer
            if videoReader.status == .reading && (sampleBuffer == videoReaderOutput.copyNextSampleBuffer()!) {
                videoWriterInput.append(sampleBuffer)

            }
            else {
                videoWriterInput.markAsFinished()
                if videoReader.status == .completed {
                    //start writing from audio reader
                    audioReader.startReading()
                    videoWriter.startSession(atSourceTime: kCMTimeZero)
                    var processingQueue = DispatchQueue(label: "processingQueue2")
                    audioWriterInput.requestMediaDataWhenReady(on: processingQueue, using: {() -> Void in
                        while audioWriterInput.isReadyForMoreMediaData {
                            var sampleBuffer: CMSampleBuffer
                            if audioReader.status == .reading && (sampleBuffer == (audioReaderOutput.copyNextSampleBuffer()!)) {
                                audioWriterInput.append(sampleBuffer)
                            }
                            else {
                                audioWriterInput.markAsFinished()
                                if audioReader.status == .completed {
                                    videoWriter.finishWriting(completionHandler: {() -> Void in
                                        self.sendMovieFile(at: outputURL)
                                    })
                                }
                            }
                        }
                    })
                }
            }

        }
    })
}

Answer 1

我不明白你为什么需要这一行：

    DictionaryLiteral : (Key: AVVideoCodecKey, Object: AVVideoCodecH264),

看到链接的线程，你可以这样写：

    var videoWriterCompressionSettings: [String: AnyObject] = [
        AVVideoAverageBitRateKey : 1250000 as NSNumber
    ]

    var videoWriterSettings : [String: AnyObject] = [
        AVVideoCodecKey: AVVideoCodecH264 as NSString,
        AVVideoCompressionPropertiesKey : videoWriterCompressionSettings as NSDictionary,
        AVVideoWidthKey : videoSize.width as NSNumber,
        AVVideoHeightKey : videoSize.height as NSNumber
    ]

    var videoWriterInput = AVAssetWriterInput(mediaType: AVMediaTypeVideo, outputSettings: videoWriterSettings)

(有人更喜欢 [String: Any] 而不是 [String: AnyObject]，说 Swifty 在 Swift 3. 使用 Any，你可以删除一些铸件，但可能会错误地包含一些只有在运行时才会显示的坏东西。）

您的代码中另一个非常糟糕的部分是 as! [String : Any?]。您需要将 [String: Any]? 传递给 AVAssetWriterInput.init(mediaType:outputSettings:)，而不是 [String: Any?]。

（可能还有其他不好的地方，我没查到。。。）

Dictionary Literal<_,_> 类型的值在强制转换中不符合 'Any'

Value of type DictionaryLiteral<_,_> does not conform to 'Any' in coersion

objective-c

avfoundation

ios

avassetwriter

swift