ios - Swift - 从 CMSampleBuffer 获取 kCMSampleBufferAttachmentKey_DroppedFrameReason

Question

我想了解为什么我的 AVCaptureOutput 丢帧。在 captureOutput(_ output: AVCaptureOutput, didDrop sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) 委托(delegate)方法中，我得到一个 CMSampleBuffer 应该包含一个解释框架原因的附件已删除 ( doc )

原因预计是这些 CFString 之一:

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

从文档中确实不清楚如何获取此值。我试过使用 CMGetAttachment 但这会返回一个 CMAttachmentMode 又名 UInt32:

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

而且我真的不知道如何将这个 UInt32 与 CFString 常量相匹配

Answer 1

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)