FFMPEG - "top coded first" ?

[dave007]

greetings,

while using ffmpeg to encode some files, i noticed that it often provides four interlaced different scan modes (for example with -field_order) instead of just two : top field first ; bottom field first ; top coded first, bottom displayed first ; and bottom coded first, top displayed first. the first two (tff, bff) i'm familiar with. does anyone know definitively what the other two are? i'd assume that they might refer to the way the video is stored within the container ; perhaps the top field is stored first in the stream, but nevertheless the decoder should display it after reading the following field in the stream ? although frankly i'm not sure, and i've found exactly zero information on this. does anyone know ?