I wrote a small demo of a VLC mediaplayer with 2 buttons : play and stop
and 1 slider for the volume.
The slider works when the player is playing, i.e. the volume is changing depending on the slider setting.
when it is stopped and the slider position is changed I need to click on play 2 times to make the volume changing according to the new setting of the slider. clicking 1 time only keeps the previous setting of the volume.
Here is the code :