Trouble with transitions

Having trouble with transitions, feeding flac files. If written like this:

settings.frame.audio.channels.set(2)
settings.frame.audio.samplerate.set(96000)

music = playlist(reload_mode="watch","/Musik")

live = input.harbor("live", port=18888, password="hackme")

def to_show(a, b) 
  add(normalize=false, [
    fade.out(a),
    sequence([blank(duration=2.), (b.source)]),
  ])
end
radio=fallback(track_sensitive=false, transition_length=5., transitions=[to_show],[live, music])

output.icecast(%mp3(bitrate=256,samplerate=44100), fallible=true, mount="source.mp3", radio)

it crashes with

2021/09/14 22:14:38 [switch_0:3] Switch to playlist_0.
2021/09/14 22:14:54 [input.harbor_0:3] Decoding...
2021/09/14 22:14:54 [input.harbor_0:3] New metadata chunk Mother Earth Radio -- Musikvorstellung.
2021/09/14 22:14:56 [switch_0:3] Switch to input.harbor_0 with transition.
2021/09/14 22:14:56 [clock.main:2] Source source.mp3 failed while streaming: Lang_values.Internal_error at at bug.liq, line 13, char 9-17, at bug.liq, line 11 char 0 - line 16 char 3: invoked method source not found!
2021/09/14 22:14:56 [source.mp3:3] Closing connection...

written like this

def to_show(a, b) 
add(normalize=false, [
sequence([fade.out(a), blank(duration=2.), (b)]),
])
end

it doesn't do any fading. Lastly

def to_show(a, b) 
crossfade(b)
end

gives

2021/09/14 22:20:49 [switch_0:3] Switch to input.harbor_0 with transition.
2021/09/14 22:20:49 [clock.main:2] Source source.mp3 failed while streaming: Clock_conflict: At position: unknown position, a source cannot belong to two clocks (cross_0.child[], main[])!

obviously that is just done wrong, looking at the clocks message. I try to have a transition at the switch to live show that fades out the regular stream inserts blank and starts the source with no fading.

Its a raspbian buster, RPI4, installed via opam, ffmpeg pinned from github

2021/09/14 22:24:13 >>> LOG START
2021/09/14 22:24:11 [main:3] Liquidsoap 2.0.0-rc1
2021/09/14 22:24:11 [main:3] Using: graphics=[distributed with Ocaml] bytes=[distributed with OCaml 4.02 or above] pcre=7.4.6 sedlex=2.4 menhirLib=20210419 curl=0.9.1 dtools=0.4.4 duppy=0.9.2 cry=0.6.5 mm=0.7.1 ogg=0.7.0 ogg.decoder=0.7.0 mad=0.5.0 flac=0.3.0 flac.ogg=0.3.0 flac.decoder=0.3.0 dynlink=[distributed with Ocaml] lame=0.3.4 ffmpeg-avutil=7d8a3b1 ffmpeg-avcodec=7d8a3b1 ffmpeg-avdevice=7d8a3b1 ffmpeg-av=7d8a3b1 ffmpeg-avfilter=7d8a3b1 ffmpeg-swresample=7d8a3b1 ffmpeg-swscale=7d8a3b1 samplerate=0.1.6 taglib=0.3.6 ssl=0.5.9 camomile=1.0.2 tsdl=v0.9.8 camlimages=4.2.6
2021/09/14 22:24:11 [dynamic.loader:3] Could not find dynamic module for fdkaac encoder.
2021/09/14 22:24:11 [clock:3] Using builtin (low-precision) implementation for latency control
2021/09/14 22:24:13 [frame:3] Using 96000Hz audio, 25Hz video, 96000Hz main.
2021/09/14 22:24:13 [frame:3] Video frame size set to: 1280x720
2021/09/14 22:24:13 [frame:3] Frame size must be a multiple of 3840 ticks = 3840 audio samples = 1 video samples.
2021/09/14 22:24:13 [frame:3] Targeting 'frame.duration': 0.04s = 3840 audio samples = 3840 ticks.
2021/09/14 22:24:13 [frame:3] Frames last 0.04s = 3840 audio samples = 1 video samples = 3840 ticks.
2021/09/14 22:24:13 [sandbox:3] Sandboxing disabled
2021/09/14 22:24:13 [video.converter:3] Using preferred video converter: ffmpeg.
2021/09/14 22:24:13 [audio.converter:3] Using samplerate converter: ffmpeg.
2021/09/14 22:24:13 [harbor:3] Adding mountpoint '/live' on port 18888
2021/09/14 22:24:13 [source.mp3:3] Connecting mount source.mp3 for source@localhost...
2021/09/14 22:24:13 [source.mp3:3] Connection setup was successful.
2021/09/14 22:24:13 [clock.main:3] Streaming loop starts in auto-sync mode
2021/09/14 22:24:13 [clock.main:3] Delegating synchronisation to CPU clock
2021/09/14 22:24:13 [source.mp3:3] Source failed (no more tracks) stopping output...
2021/09/14 22:24:13 [source.mp3:3] Closing connection...
2021/09/14 22:24:14 [playlist_0:3] Prepared "/media/pi/Elements 4TB/FTP Mother Earth/Musik/Feist/09 Undiscovered First.flac" (RID 0).
2021/09/14 22:24:14 [source.mp3:3] Connecting mount source.mp3 for source@localhost...
2021/09/14 22:24:14 [source.mp3:3] Connection setup was successful.
2021/09/14 22:24:14 [switch_0:3] Switch to playlist_0.
2021/09/14 22:25:01 [input.harbor_0:3] Decoding...
2021/09/14 22:25:01 [input.harbor_0:3] New metadata chunk Mother Earth Radio -- Musikvorstellung.
2021/09/14 22:25:03 [switch_0:3] Switch to input.harbor_0 with transition.
2021/09/14 22:25:03 [clock.main:2] Source source.mp3 failed while streaming: Lang_values.Internal_error at at bug.liq, line 14, char 31-39, at bug.liq, line 11 char 0 - line 16 char 3: invoked method source not found!
2021/09/14 22:25:03 [source.mp3:3] Closing connection...
2021/09/14 22:25:03 [harbor:3] Removing mountpoint '/live' on port 18888
2021/09/14 22:25:03 [harbor:3] Nothing more on port 18888: closing sockets.
2021/09/14 22:25:03 [clock:2] Error when leaving output source.mp3: File "sources/request_source.ml", line 339, characters 10-16: Assertion failed!
2021/09/14 22:25:03 [clock.main:3] Streaming loop stopped.
2021/09/14 22:25:03 [main:3] Shutdown started!
2021/09/14 22:25:03 [main:3] Waiting for main threads to terminate...
2021/09/14 22:25:04 [input.harbor_0:2] Error while reading from client: Bad file descriptor in select()
Invalid return value 0 for stream protocol
2021/09/14 22:25:04 [input.harbor_0:2] Feeding stopped: Failure("relaying stopped").
2021/09/14 22:25:04 [main:3] Main threads terminated.
2021/09/14 22:25:04 [threads:3] Shutting down scheduler...
2021/09/14 22:25:04 [threads:3] Scheduler shut down.
2021/09/14 22:25:04 [main:3] Cleaning downloaded files...
2021/09/14 22:25:04 [main:3] Freeing memory...

savonet / liquidsoap

Trouble with transitions #1929