Recently been working on a TV Commercial and they asked for it as upper field first rather than progressive can any one explain the difference between the two and why upper field first is requested for TV?
Upper field first is a form of interlacing. Interlacing divides each frame of video into two fields, with each field containing half of the scan lines of the frame. One field contains the first, third, fifth, and so on lines while the other frame contains the second, fourth, sixth, etc. lines. That alternation of lines is what makes it interlaced.
Different coding methodologies define whether the field that contains the first line of video is described first or second. Upper field first means that the field that contains the first line of video is sent first in a frame. Lower field first sends the field with the first line of video second in the frame.
Progressive video does not divide a frame into fields. Every line of video is described every time a frame changes.
The region and the specifications of the individual broadcaster will determine whether they want a progressive, top-first interlaced, or bottom-first interlaced vide. In general, HD video is always upper field first. SD video is usually lower field first, but it depends on the exact standard being used. These settings are true whether you are delivering to an over the air broadcaster, a cable service provider, or just playing your video on a TV.