This is what the function does:
```
switch (_BIS_fadeInOrOut) do
{
case 0:
{
...
_BIS_fadeDuration fadeSound 0;
_BIS_fadeDuration fadeMusic 0;
_BIS_fadeDuration fadeSpeech 0;
...
};
case 1:
{
...
0 fadeSound 0;
0 fadeSpeech 0;
...
_BIS_fadeDuration fadeSound 1;
_BIS_fadeDuration fadeSpeech 1;
...
}
};
```
In other words, if someone uses the function in "fade out" mode (`[0,"BLACK",3,1] spawn BIS_fnc_fadeEffect;`), they can't go back to normal using `[1,"BLACK",3,1] spawn BIS_fnc_fadeEffect`
But at the same time, I don't think it is necessary to use `0 fadeMusic 0;` at the start of case 1. (it changes the behavior of this function)
you only need:
`_BIS_fadeDuration fadeMusic 1;`