ios - 如何限制 AVAssetWriter 在编码视频时使用过多内存？

Question

我使用 AVAssetWriter 生成带有帧图像的视频(UIImage 数组)。当它进行编码工作时，内存使用量有时会飙升至超过 700MB。在我的 iPhone(配备 3GB MEM)上，这不会导致 OOM 问题，但我担心它会在旧款 iPhone 上造成问题。

我能以某种方式限制 AVAssetWriter 内存使用吗？我猜在内部它可能使用一些队列来缓存帧字节，如果我可以指定缓存的大小，那么我可以设置内存的上限。但是我没有在文档中找到这样的选项/设置。

这是我的代码:

    let settings:[String:Any] = [
        AVVideoCodecKey: AVVideoCodecH264,
        AVVideoWidthKey: FRAME_SIZE,
        AVVideoHeightKey: FRAME_SIZE
    ]
    let assetWriter = AVAssetWriter(url: self.url!, fileType: AVFileType.mov)        
    let assetWriterInput = AVAssetWriterInput(mediaType: AVMediaType.video, outputSettings: settings)
    self.assetWriter?.add(assetWriterInput)

    let bufferAttributes:[String: Any] = [kCVPixelBufferPixelFormatTypeKey as String: Int(kCVPixelFormatType_32ARGB)]
    let bufferAdapter = AVAssetWriterInputPixelBufferAdaptor(assetWriterInput: assetWriterInput, sourcePixelBufferAttributes: bufferAttributes)
    let frameTime = CMTimeMake(1, 30)

    self.assetWriter?.startWriting()
    self.assetWriter?.startSession(atSourceTime: kCMTimeZero)

    let mediaInputQueue = DispatchQueue(label: "mediaInputQueue")

    var i = 0

    assetWriterInput.requestMediaDataWhenReady(on: mediaInputQueue){
        var localframes = frames
        while(true){
            if(localframes.isEmpty){
                break
            }
            if (assetWriterInput.isReadyForMoreMediaData){
                let image = localframes.removeFirst()
                let pixelBuffer = self.newPixelBufferFrom(cgImage: image.cgImage!)

                var time:CMTime
                if i == 0 {
                    time = kCMTimeZero
                } else {
                    time = CMTimeMake(Int64(i), frameTime.timescale)
                }

                bufferAdapter.append(pixelBuffer!, withPresentationTime: time)

                // TODO: how to release memory?
                i += 1
            }
        }
        assetWriterInput.markAsFinished()
        self.assetWriter?.finishWriting(completionHandler: {
                finishedHandler()
        })
    }

Answer 1

不确定它是否有帮助，但我在 while 循环中遇到了类似的问题。您可以查看此答案:Is the ios iPhone simulator causing memory usage analysis to swell?

您可以尝试一下，看看它是否有所改善:

let pixelBuffer = autoreleasepool { return self.newPixelBufferFrom(cgImage: image.cgImage!) }