This question is very similar to Re: FX3 SD video encoder
In case you would like to use Interace, you need to set "Interlace Flags" in "Class specific Uncompressed VS format descriptor" appropriately.
By default of AN75779, "Interlace Flags" is 0x00 that stands for Progressing scan. Change this field what the customer wants.
The meaning of this Field can confirm by reading "USB_Video_Payload_Frame_Based_1.1 or 1.5.pdf" and please check the offset 25 'bmInterlaceFlags' that is Specifies interlace information.