Swift - 從CMSampleBuffer獲取kCMSampleBufferAttachmentKey_DroppedFrameReason

Question

我想了解爲什麼我的AVCaptureOutput丟幀。在captureOutput(_ output: AVCaptureOutput, didDrop sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection)委託方法，我得到的是應該包含一個附件解釋框架被丟棄的原因（doc）一CMSampleBuffer

原因是預計這些CFString字符串之一：

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

從文檔真的不清楚如何獲得這個價值。我已經使用CMGetAttachment嘗試，但這種返回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 
} 

，我真的不知道如何將這種UInt32的匹配到CFString字符串常量

Answer 1

我愣神不看右輸出：

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