Object category's labeling confidence of this track.
Different representation of tracking info in non-streaming
batch and streaming modes.
Streaming mode ONLY. In streaming mode, we do not know the end
time of a tracked object before it is completed. Hence, there
is no VideoSegment info returned. Instead, we provide a unique
identifiable integer track_id so that the customers can
correlate the results of the ongoing ObjectTrackAnnotation of
the same track_id over time.