So, if I understand correctly from your code, you are trying to get per frame the time remaining for the sound playing to finish?
I think you just need to grab a reference to the sound instance playing, not to the sound slot:
var TestSoundCurTime = pc.createScript('testSoundCurTime');
// initialize code called once per entity
TestSoundCurTime.prototype.initialize = function() {
this.soundTogetCurrTime = this.entity.sound.slot("test");
console.log("stgs: "+this.soundTogetCurrTime.name);
this.soundInstance = this.playSound();
};
// update code called every frame
TestSoundCurTime.prototype.update = function(dt) {
console.log("getCurTim - duration: ", this.soundInstance.currentTime - this.soundTogetCurrTime.duration);
};
TestSoundCurTime.prototype.playSound = function(){
return this.entity.sound.play("test");
};