Ios Swift-从CMSampleBuffer获取kCMSampleBufferAttachmentKey_DroppedFrameReason

我试图理解为什么我的AVCaptureOutput正在删除帧。在

captureOutput（\uoutput:AVCaptureOutput，didDrop-sampleBuffer:CMSampleBuffer，from-connection:AVCaptureConnection）

delegate方法中，我得到了一个

CMSampleBuffer

，它应该包含一个附件，解释删除帧的原因（）

原因可能是以下原因之一：

kCMSampleBufferDroppedFrameReason_FrameWasLate // "FrameWasLate"
kCMSampleBufferDroppedFrameReason_OutOfBuffers // "OutOfBuffers"
kCMSampleBufferDroppedFrameReason_Discontinuity // "Discontinuity"

从文档中我们真的不清楚如何得到这个值。我尝试使用

CMGetAttachment

，但这会返回

CMAttachmentMode

aka

UInt32

：

func captureOutput(_ output: AVCaptureOutput, didDrop sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {
  var reason: CMAttachmentMode = 0
  CMGetAttachment(sampleBuffer, kCMSampleBufferAttachmentKey_DroppedFrameReason, &reason)
  print("reason \(reason)") // 1
}

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我真的不知道如何将UInt32与CFString常量匹配

我愚蠢地没有看到正确的输出：

var mode: CMAttachmentMode = 0
let reason = CMGetAttachment(sampleBuffer, kCMSampleBufferAttachmentKey_DroppedFrameReason, &mode)
print("reason \(String(describing: reason))") // Optional(OutOfBuffers)