Unity Project

reference
https://cardgames.io/yahtzee/

Library/PackageCache/com.unity.timeline@1.2.15/Editor/Manipulators/Sequence/TrackZoom.cs

@@ -0,0 +1,20 @@
+using UnityEngine;
+using UnityEngine.Timeline;
+
+namespace UnityEditor.Timeline
+{
+    class TrackZoom : Manipulator
+    {
+        // only handles 'vertical' zoom. horizontal is handled in timelineGUI
+        protected override bool MouseWheel(Event evt, WindowState state)
+        {
+            if (EditorGUI.actionKey)
+            {
+                state.trackScale = Mathf.Min(Mathf.Max(state.trackScale + (evt.delta.y * 0.1f), 1.0f), 100.0f);
+                return true;
+            }
+
+            return false;
+        }
+    }
+}