update State Snapshots canApply when snapshots are added

src/extensions/mp4-export/controls.ts

@@ -125,17 +125,20 @@ export class Mp4Controls extends PluginComponent {
         this.subscribe(this.plugin.canvas3d?.resized!, () => this.syncInfo());
         this.subscribe(this.plugin.helpers.viewportScreenshot?.events.previewed!, () => this.syncInfo());
 
-        this.subscribe(this.plugin.behaviors.state.isBusy, b => {
-            const anim = this.current;
-            if (!b && anim) {
-                this.behaviors.canApply.next(anim.anim.canApply?.(this.plugin) ?? { canApply: true });
-            }
-        });
+        this.subscribe(this.plugin.behaviors.state.isBusy, b => this.updateCanApply(b));
+        this.subscribe(this.plugin.managers.snapshot.events.changed, b => this.updateCanApply(b));
 
         this.sync();
         this.syncInfo();
     }
 
+    private updateCanApply(b?: any) {
+        const anim = this.current;
+        if (!b && anim) {
+            this.behaviors.canApply.next(anim.anim.canApply?.(this.plugin) ?? { canApply: true });
+        }
+    }
+
     constructor(private plugin: PluginContext) {
         super();