mono mode

[bbd666]

How to play a file in mono mode ?
I've tried
player.audio_output_set('Mono')
But changed nothing, i.e still in stereo mode.

Here is my code :

import time
import vlc

url='test.mp3' 
player = vlc.MediaPlayer()
media=vlc.Media(url)
player.set_media(media)
#player.set_mrl(url)
s=player.audio_output_device_enum()
print(s)
s=player.audio_output_set('Mono')
print(s)
player.play()
time.sleep(60)

returns :

<vlc.LP_AudioOutputDevice object at 0x7fba66a5550>
-1

PS : when I run the VLC multimedia player and I select Audio/stereo mode/Mono, it works fine (i.e downmix a stereo file into mono mode). I'm using a Rpi Pi3, OS Trixie (no PulseAudio) with a headset plugged on the jack.