奇场的最后一行，该行只有前一半的数据是有效的视频数据，提示接下来的场是偶场；
偶场的最后一行都是有效视频数据，提示接下来的场是奇场。
At the end of an odd field, there is an extra half line of data that is sent indicating the following field is even. Similarly, the last line of the even field is a full line of active video data, indicating the following field will be odd.
图片摘自National Instrument网站。
http://digital.ni.com/public.nsf/allkb/17A032D78871F03086256B610057C984