private void setUserData(EffectTrack effectTrack) {
        //fetching the UserData TrackInfo.
        TrackInfo data = (TrackInfo) effectTrack.emitter.getUserData("TrackInfo");

        //if it does not exist, we create it and attach it to the emitter.
        if (data == null) {
            data = new TrackInfo();
            effectTrack.emitter.setUserData("TrackInfo", data);
        }

        //adding the given Track to the TrackInfo.
        data.addTrack(effectTrack);
    }
set the start offset of the track

@param startOffset the start offset (in seconds)
jme3-core/src/main/java/com/jme3/animation/EffectTrack.java