# Tweaked custom crossfade to deal with jingles..
def smart_cross(~start_next=5.,~fade_in=3.,~fade_out=3.,
                ~default=(fun (a,b) -> sequence([a, b])),
                ~high=-15., ~medium=-32., ~margin=4.,
                ~width=2.,~conservative=false,s)
    fade.out = fade.out(type="sin", duration=fade_out)
    fade.in  = fade.in(type="sin", duration=fade_in)
    add = fun (a,b) -> add(normalize=false, [b, a])
    log = log(label="smart_cross")

    def transition(a,b,ma,mb,sa,sb)
        list.iter(fun(x)-> log(level=4, "Before: #{x}"), ma)
        list.iter(fun(x)-> log(level=4, "After : #{x}"), mb)

        if ma["type"] == "J" or mb["type"] == "J" then
            log("Old or new file is a jingle: sequenced transition.")
            sequence([sa, sb])
        elsif
            # Do not fade if it's already very low.
            b >= a + margin and a <= medium and b <= high
        then
            log("new >= old + margin, old <= medium and new <= high.")
            log("Do not fade if it's already very low.")
            log("Transition: crossed, no fade.")
            add(sa, sb)

            # What to do with a loud end and a quiet beginning ?
            # A good idea is to use a jingle to separate the two tracks,
            # but that's another story.
        else
            # Otherwise, A and B are just too loud to overlap nicely,
            # or the difference between them is too large and overlapping would
            # completely mask one of them.
            # log("No transition: using default.")
            # default(sa, sb)
            log("Transition: crossed, fade-in, fade-out.")
            add(fade.out(sa), fade.in(sb))
        end
    end

    cross(width=width, duration=start_next,
          conservative=conservative, transition,s)
end