Can't get any video crossfade to work

[evaninf]

I'm using liquidsoap 2.2.5 and trying the example in the book:

s = playlist("videos.playlist")
s = video.fade.out(duration=1., s)
s = video.fade.in (duration=1., s)
s = cross(duration=1.5, fun (a,b) -> add([a.source, b.source]), s)

But in doesn't work as it suggests, all video tracks start as usual without any fade.

A different variant:

vid = single("video.mp4")
vid = video.fade.in(vid, duration=5., transition="slide_right")

I have tried several combinations, playlists, transitions, durations, fade.in instead of video.fade.in, etc... I can't get any fading or sliding on any video, they always result in normally attached videos without any transition.

Is this actually supported?