assetWrite.status AVAssetWriterStatusUnknown

[niuguoning]

• (void)finishWritingWithCompletionHandler:(void (^)(void))handler
  {
  if (_assetWriter.status == AVAssetWriterStatusUnknown ||
  _assetWriter.status == AVAssetWriterStatusCompleted) {
  DLog(@"asset writer was in an unexpected state (%@)", @(_assetWriter.status));
  return;
  }
  [_assetWriterVideoInput markAsFinished];
  [_assetWriterAudioInput markAsFinished];
  [_assetWriter finishWritingWithCompletionHandler:handler];
  }

It seems like when I'm running this code, the assetWriter.status is AVAssetWriterStatusUnknown, so that vision(vision: PBJVision, capturedVideo videoDict: [NSObject : AnyObject]?, error: NSError?) never gets called.