为liquidsoap回退创建处理程序

Question

我想知道liquidsoap何时回退到emergency_playlist，以便我可以启动系统脚本。也许有一个处理程序可以执行类似on_blank（处理程序，无线电），

这是我的代码，

#!/home/ubuntu/.opam/system/bin/liquidsoap
myplaylist = playlist("~/backup_playlist/playlist/Emergency-list.m3u",mode="normal")
backup_playlist = audio_to_stereo(myplaylist) 
liveset = input.http("http://listen.qkradio.com.au:8382/main_test.mp3")
radio = fallback(track_sensitive=false,
         [strip_blank(max_blank=120.,liveset), backup_playlist])
radio = on_blank(handler,radio)

 # Stream it out
output.icecast(
%mp3(bitrate=64),
host="localhost", port=8382, password="xxxxxxxx", 
mount="test.mp3",  radio)

更新

以下代码执行系统脚本但是只有在脚本启动时才会执行，但我希望每次启动回退时执行此操作

def fall()
   system("./scripts/pushover.py")
   backup_playlist
end

radio = fallback(track_sensitive=false,
         [strip_blank(max_blank=10.,liveset), fall() , security])