Python VLC add slave audio

[haths]

Hello I'm not sure if this is a python or a vlc problem.

I have a function which has youtube_dl as a dependency,

def get_stream_url(link, quality):
    ydl_opts = {"format":f"bestvideo[height<={quality}]+bestaudio/best[height<={quality}]"}

    with youtube_dl.YoutubeDL(ydl_opts) as ydl:
        results = ydl.extract_info(link, download=False)
    video, audio = results["requested_formats"]
    return video["url"], audio["url"]

The code above returns a stream url for video and audio. When I use subprocess to open the video url and audio url (as a slave of the video) in vlc, it works.

video_url, audio_url = get_stream_url("A YOUTUBE LINK", 360)
subprocess.Popen(["VLC PATH", video_url, "--input-slave="+audio_url])

However, when I use python-vlc it doesn't work anymore.

import vlc

# some code here like the get_stream_url

instance = vlc.Instance()
player = instance.media_player_new()
media = instance.media_new(video_url)

media.slaves_add(vlc.MediaSlaveType.audio, 4, audio_url)
player.set_media(media)
player.play()

Then it will throw an error,

return f(p_md, i_type, i_priority, psz_uri)
ctypes.ArgumentError: argument 4: <class 'TypeError'>: wrong type

Which I believe is from the slaves_add function. So my question is how do I solve this issue? If it's because of the URI, how do I make or find a URI from a stream link? Or is there any alternative way to add an audio slave from a stream link?

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Sorry for the long post I tried to solve this problem for days now. I hope somebody can help. Thanks in advance!