The After Effects scripting guide makes it clear how to set layer markers but I have yet to find a way to set timeline markers.
The code for setting a layer marker is as follows:
var myMarker = new MarkerValue("Fade Up");
myLayer.property("Marker").setValueAtTime(2, myMarker);
I would like to add a marker to the timeline but calling the same function on an item returns undefined.
app.project.item[i].property("Marker").setValueAtTime(2, myMarker);
How can I access timeline markers?
Well, it's not officially supported to grab timeline comp markers via AE's Scripting API, but it is possible via scripting. Check out Paul Tuersley's solution on this thread at the Adobe forums. I implemented it and it's working fine.