crossfade sample code

[Nicolas-Imago]

Hi guys, for a web radio project we implemented a very simple radio with liquidsoap :

playlist = playlist("/var/www/html/mp3")
live = input.http("http://localhost:8000/live.mp3")
radio = fallback(track_sensitive=false, [live, playlist])
output.icecast(%mp3, host = "localhost", port = 8000, password = "PWD", mount = "webradio.mp3", mksafe(radio))

The idea is to have a playlist (all day long) that we can interrupt at any time by a live.
And it works perfectly !

But now we would like to improve adding a fading transition from playlist to live and from live to playlist.

We tried to find help here and had a look to the documentation.
But we could not found.

We tried (advised by Chat GPT) to add :
radio_fading = crossfade(start_next=true, fade_in=2.0, fade_out=2.0, [live, playlist])
and changed last line as :
output.icecast(%mp3, host = "localhost", port = 8000, password = "PWD", mount = "webradio.mp3", mksafe(radio_fading))

but it doesn't work.
I guess solution is very simple ?

Nicolas

[Moonbase59]

Never trust an "AI" to generate working code! There is no start_next in crossfade. Docs here → https://www.liquidsoap.info/doc-dev/reference.html#crossfade, Cookbook here → https://www.liquidsoap.info/doc-dev/cookbook.html.

Then there’s also "The Book"—really worth reading. → https://www.liquidsoap.info/doc-dev/book.html

[Nicolas-Imago]

Thanks Moonbase59 for your help.

You right, with Chat GPT implementation, I had an error about "start_next", so I removed it yesterday but I had another error message

_At mux.liq, line 38, char 55-71:
radio_fading = crossfade(fade_in=2.0, fade_out=2.0, [live, playlist])

Error 5: this value has type
[]
but it should be a subtype of the type of the value at /usr/share/liquidsoap/2.1.3/libs/fades.liq, line 369, char 58
source()_

I also read the 2 links you suggest (before to post my message yesterday) and I could not understand how to implement.
Unfortunately, there is no sample :(

Do you know the line I should implement to replace :
radio_fading = crossfade(fade_in=2.0, fade_out=2.0, [live, playlist])

Thanks a lot in advance
Nicolas

[Nicolas-Imago]

Hi ! Moonbase59, any other helper to help us ? ;)

[Moonbase59]

Well, you already have a fallback in your original code, which supports specifying transition functions, so you could easily add one each for the transitions playlist → live and live → playlist, as shown in the Cookbok:

# Transition to live
def to_live(playlist, live) =
  #sequence([playlist,live])
  add([fade.in(duration=2.0, live), fade.out(duration=2.0, playlist)])
end

# Transition back to playlist
def to_playlist(live, playlist) =
  #sequence([live, playlist])
  add([fade.in(duration=2.0, playlist), fade.out(duration=2.0, live)])
end

radio = fallback(
  track_sensitive=false,
  transitions=[to_live, to_playlist],
  [live, playlist]
)

Out of my head, not tested. I just replaced the suggested sequence from the Cookbook with an add that allows the fades to be specified.

— or —

If you really wanted to use a crossfade instead, which would also crossfade the playlist tracks, just use the source instead of a list of sources (your Error 5: []):

radio = crossfade(fade_in=2.0, fade_out=2.0, radio)

Notice the subtle differences:

• fade.in in the add is a function, while
• fade_in in the crossfade is just a parameter given to the crossfade function.

Learn Liquidsoap, it’s not so easy but eventually pays, and you can do anything!

[Nicolas-Imago]

Thanks for your help.
I couldn't make work crossfade with your suggested code, I still have the same error 5.

But I managed to test your suggested code with "add" function. I works, but it seems not to work as it should.

I also found the book here : https://www.liquidsoap.info/book/book.pdf
I started to read it to understand better how crossfade works.

Thanks.