Question

我正在尝试根据使用Obj-C（How can I reduce the file size of a video created with UIImagePickerController?）的SO帖子在swift中设置自定义视频压缩。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上突出显示。压缩功能如下：

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

我不明白为什么你需要这一行：

看到链接的线程，你可以这样写：

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

（有人比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)更喜欢[String: Any]，说它在Swift 3中更加Swifty。使用[String: AnyObject]，你可以移除一些石头，但可能会错误地包含一些错误只会在运行时显示的东西。）

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

（可能还有其他一些不好的部分，我没有检查过......）

DictionaryLiteral＆lt; _，_＆gt;类型的值在coersion中不符合'Any'

1 个答案: