[MPlayer-users] how to set mpi->fields?

[boku]

Dear all,
     I'm writing the wrapper, vd_xxx.c. And have some questions about
mpi->fields. It can have 4 kinds of different
#define MP_IMGFIELD_ORDERED 0x01
#define MP_IMGFIELD_TOP_FIRST 0x02
#define MP_IMGFIELD_REPEAT_FIRST 0x04
#define MP_IMGFIELD_TOP 0x08
#define MP_IMGFIELD_BOTTOM 0x10
#define MP_IMGFIELD_INTERLACED 0x20

I don't know which one I should set if the decoder only decodes frame (no
interlaced).
And in interlace mode, one mpi has only one interlaced picture, right?
The mplayer uses this field to check the picture is top or bottom?