Heya o/
So for these custom tracks since you’re using the Customizable Sequencer Tracks I should be able to help a bit.
In the OnInputAdded event you get an object reference to the Section this event is being triggered on (of type UMovieSceneSection).
If you get the Outer object of this, you can get a reference to the Track (UMovieSceneTrack).
The Outer object of the Track is the UMovieScene.
The Outer object of the MovieScene is the ULevelSequence.
Unfortunately there’s no great way I know of to get the actual LevelSequenceActor.
But you could do a Get All Actors of Class and then for each LevelSequenceActor check if the sequence they have assigned is the same as the LevelSequence of your Section.
If it is, you know this is your LevelSequenceActor (as an extra check you may want to see if the LevelSequenceActor is actually playing, otherwise you might get issues if there are multiple LevelSequenceActors in your world that are all set to play the same sequence).
Now that you have a reference to your LevelSequenceActor you can get its LevelSequencePlayer and get the current frame from there.
Bit roundabout but this has worked for me. Let me know if there are better ways to do this!