[AVAssetWriter影片创建后的内存分配飞涨

Question

我的应用程序中有一个例程，可通过AVAssetWriter将MTLTextures捕获为电影。当我在设备上运行该应用程序时，内存管理似乎保持稳定，并且电影被创建并写入磁盘。但是，当我在App Store上发布该应用程序并下载该应用程序时，无论电影大小如何，该应用程序在创建电影后不久就会崩溃。通过工具运行该应用程序将显示在从MTLTextures中提取PixelBuffer的例程中发生了巨大的内存分配。这是崩溃发生的地方。该例程在我要记录的每个MTLTexture的循环中运行：

func AVAssetWriterEncodeFrame(forTexture texture: MTLTexture) {

    while !assetWriterVideoInput!.isReadyForMoreMediaData  {
    } // hang out here until isReadyForMoreMediaData == true

    autoreleasepool(invoking: { () -> () in

      let fps: Int32 = Int32(Constants.movieFPS)

      guard let pixelBufferPool = assetWriterPixelBufferInput!.pixelBufferPool else {
        print("[MovieMakerVC]: Pixel buffer asset writer input did not have a pixel buffer pool available; cannot retrieve frame")
        return
      }

      var maybePixelBuffer: CVPixelBuffer? = nil
      let status  = CVPixelBufferPoolCreatePixelBuffer(nil, pixelBufferPool, &maybePixelBuffer)
      if status != kCVReturnSuccess {
        print("[MovieMakerVC]: Could not get pixel buffer from asset writer input; dropping frame...")
        return
      }
      guard let pixelBuffer = maybePixelBuffer else { return }
      CVPixelBufferLockBaseAddress(pixelBuffer, [])
      let pixelBufferBytes = CVPixelBufferGetBaseAddress(pixelBuffer)!

      // Use the bytes per row value from the pixel buffer since its stride may be rounded up to be 16-byte aligned
      let bytesPerRow = CVPixelBufferGetBytesPerRow(pixelBuffer)
      let region = MTLRegionMake2D(0, 0, texture.width, texture.height)

      texture.getBytes(pixelBufferBytes, bytesPerRow: bytesPerRow, from: region, mipmapLevel: 0)

      let presentationTime = CMTimeMake(value: Int64(frameIndexForPresentationTime), timescale: fps)

      assetWriterPixelBufferInput!.append(pixelBuffer, withPresentationTime: presentationTime)

      CVPixelBufferUnlockBaseAddress(pixelBuffer, [])

      frameIndexForPresentationTime += frameHoldLength  // set up for next frame

    }) // end of autoreleasepool

  } // end of func AVAssetWriterEncodeFrame(forTexture texture: MTLTexture)

图形中看到的尖峰在影片被写入磁盘后会不受控制地增长。分配列表显示了数千个条目，如下所示：

@@ autoreleasepool内容。 ... 4 KiB AVFoundation。 -[AVAssetWriter输入助手]。 （如上图所示）

有人可以指出我在做什么错，希望可以解决该问题吗？

Answer 1

罪魁祸首就是这段代码：

while！assetWriterVideoInput！.isReadyForMoreMediaData {} //在这里闲逛，直到isReadyForMoreMediaData == true

事实证明，在AVAssetWriterInputPixelBufferAdaptor对象中测试这种情况的虚假性确实很糟糕。

相反，将逻辑块的整体包装如下：

var frameIsCaptured: Bool = false

while (assetWriterVideoInput!.isReadyForMoreMediaData && frameIsCaptured == false) {     
    ... // insert all the texture processing logic
    texture.getBytes(pixelBufferBytes, bytesPerRow: bytesPerRow, from: region, mipmapLevel: 0)
    ... // insert pixelBuffer ingestion logic
    frameIsCaptured = true. // needed so we only process this texture once
}

[我之前所做的事情在某种意义上说是例程将不断循环直到isReadyForMoreMediaData变为真（在这一点上，我将完成将pixelBuffer附加到正在进行的电影中所需的所有纹理工作） ，但是由该空循环创建的可笑的开销似乎并不是要解决的设计缺陷。当然，Instruments指出此循环中存在问题，但花了我一段时间才看到光。