The FID is an active-Low pin used as Field ID for AXI4-Stream bus. It is used only for interlaced video. When FID is set to 0, it is an even field and when FID is set to 1, it is an odd field. This bit is sampled coincident with the SOF on the AXI4-Stream bus. If the signal is not used (i.e., the progressive video input stream), the output must be set low.