
go fwd 
 
    previous_header = current header    ; in case we need to back up
    if play_next = EOF then 
            read current header 
            update play_next

    if play_next != EOF
        current header = play_next
    read current header
    if new fldsiz = zero & special effects
        current header = previous header
        read current header
    update words2go, & play next  from read_header
    ret

read current header:
    read_header
    if lost in vram
        current header = last capture
        read header
rts


2. field_fwd returns success, vram_read_ptr and words-2-go
& field_rev