Simple AE tempo-to-markers script

// @target aftereffects

(function createUI() {
    var dialog = new Window("palette", "Tempo Marker Generator", undefined);
    dialog.orientation = "column";
    dialog.alignChildren = ["left", "top"];
    dialog.spacing = 10;
    dialog.margins = 16;

    var bpmGroup = dialog.add("group");
    bpmGroup.orientation = "row";
    bpmGroup.spacing = 10;
    bpmGroup.add("statictext", undefined, "BPM:");
    var bpmInput = bpmGroup.add("edittext", undefined, "120");
    bpmInput.characters = 5;

    var durationGroup = dialog.add("group");
    durationGroup.orientation = "row";
    durationGroup.spacing = 10;
    durationGroup.add("statictext", undefined, "Duration (sec):");
    var durationInput = durationGroup.add("edittext", undefined, "10");
    durationInput.characters = 5;

    var buttonGroup = dialog.add("group");
    buttonGroup.orientation = "row";
    buttonGroup.spacing = 10;

    var applyButton = buttonGroup.add("button", undefined, "Apply");
    var cancelButton = buttonGroup.add("button", undefined, "Cancel");

    applyButton.onClick = function() {
        app.beginUndoGroup("Add Tempo Markers");

        try {
            var comp = app.project.activeItem;
            if (!comp || !(comp instanceof CompItem)) {
                alert("Please select a composition.");
                return;
            }

            var selectedLayers = comp.selectedLayers;
            if (selectedLayers.length === 0) {
                alert("Please select a layer.");
                return;
            }

            var bpm = parseFloat(bpmInput.text);
            var duration = parseFloat(durationInput.text);

            if (isNaN(bpm) || isNaN(duration)) {
                alert("Please enter valid numbers.");
                return;
            }

            var secondsPerBeat = 60 / bpm;

            for (var i = 0; i < selectedLayers.length; i++) {
                var layer = selectedLayers[i];
                if (!layer.property("ADBE Marker")) {
                    alert("Cannot add markers to this type of layer.");
                    continue;
                }

                var startTime = layer.inPoint;
                var endTime = startTime + duration;
                var markerProp = layer.property("ADBE Marker");
                var beatCount = 1;

                for (var time = startTime; time <= endTime; time += secondsPerBeat) {
                    var marker = new MarkerValue("Beat " + beatCount);
                    markerProp.setValueAtTime(time, marker);
                    beatCount++;
                }
            }
        } catch (e) {
            alert("Error: " + e.toString());
        }

        app.endUndoGroup();
    };

    cancelButton.onClick = function() {
        dialog.close();
    };

    dialog.show();
})();


// @target aftereffects


(function createUI() {
    var dialog = new Window("palette", "Tempo Marker Generator", undefined);
    dialog.orientation = "column";
    dialog.alignChildren = ["left", "top"];
    dialog.spacing = 10;
    dialog.margins = 16;


    var bpmGroup = dialog.add("group");
    bpmGroup.orientation = "row";
    bpmGroup.spacing = 10;
    bpmGroup.add("statictext", undefined, "BPM:");
    var bpmInput = bpmGroup.add("edittext", undefined, "120");
    bpmInput.characters = 5;


    var durationGroup = dialog.add("group");
    durationGroup.orientation = "row";
    durationGroup.spacing = 10;
    durationGroup.add("statictext", undefined, "Duration (sec):");
    var durationInput = durationGroup.add("edittext", undefined, "10");
    durationInput.characters = 5;


    var buttonGroup = dialog.add("group");
    buttonGroup.orientation = "row";
    buttonGroup.spacing = 10;


    var applyButton = buttonGroup.add("button", undefined, "Apply");
    var cancelButton = buttonGroup.add("button", undefined, "Cancel");


    applyButton.onClick = function() {
        app.beginUndoGroup("Add Tempo Markers");

        try {
            var comp = app.project.activeItem;
            if (!comp || !(comp instanceof CompItem)) {
                alert("Please select a composition.");
                return;
            }


            var selectedLayers = comp.selectedLayers;
            if (selectedLayers.length === 0) {
                alert("Please select a layer.");
                return;
            }


            var bpm = parseFloat(bpmInput.text);
            var duration = parseFloat(durationInput.text);


            if (isNaN(bpm) || isNaN(duration)) {
                alert("Please enter valid numbers.");
                return;
            }


            var secondsPerBeat = 60 / bpm;


            for (var i = 0; i < selectedLayers.length; i++) {
                var layer = selectedLayers[i];
                if (!layer.property("ADBE Marker")) {
                    alert("Cannot add markers to this type of layer.");
                    continue;
                }


                var startTime = layer.inPoint;
                var endTime = startTime + duration;
                var markerProp = layer.property("ADBE Marker");
                var beatCount = 1;

                for (var time = startTime; time <= endTime; time += secondsPerBeat) {
                    var marker = new MarkerValue("Beat " + beatCount);
                    markerProp.setValueAtTime(time, marker);
                    beatCount++;
                }
            }
        } catch (e) {
            alert("Error: " + e.toString());
        }


        app.endUndoGroup();
    };


    cancelButton.onClick = function() {
        dialog.close();
    };


    dialog.show();
})();