Fix --video producing black frames without --viz kit (issue #5052)

source/isaaclab/config/extension.toml

@@ -1,7 +1,7 @@
 [package]
 
 # Note: Semantic Versioning is used: https://semver.org/
-version = "4.5.16"
+version = "4.5.17"
 
 # Description
 title = "Isaac Lab framework for Robot Learning"

source/isaaclab/docs/CHANGELOG.rst

@@ -1,6 +1,17 @@
 Changelog
 ---------
 
+4.5.17 (2026-03-18)
+~~~~~~~~~~~~~~~~~~~
+
+Fixed
+^^^^^
+
+* Fixed :meth:`~isaaclab.sim.SimulationContext.render` not calling ``app.update()`` when
+  running with Isaac Sim (Kit) and no active visualizer pumps the Kit app loop. This caused
+  ``--video`` recording to produce black frames when not using ``--viz kit``.
+
+
 4.5.16 (2026-03-10)
 ~~~~~~~~~~~~~~~~~~~
 

source/isaaclab/isaaclab/sim/simulation_context.py

@@ -604,6 +604,21 @@ def render(self, mode: int | None = None) -> None:
             for callback in self._render_callbacks.values():
                 callback(None)  # Pass None as event data
 
+        # When running with Isaac Sim (Kit) and no active visualizer already pumps the Kit
+        # app loop, call app.update() so the viewport and replicator render products
+        # (used e.g. by gym.wrappers.RecordVideo with render_mode="rgb_array") are refreshed.
+        # KitVisualizer.pumps_app_update() returns True and calls app.update() in its own
+        # step(), so we skip this call to avoid double-rendering in that case.
+        if has_kit() and not any(v.pumps_app_update() for v in self._visualizers):
+            try:
+                import omni.kit.app
+
+                app = omni.kit.app.get_app()
+                if app is not None and app.is_running():
+                    app.update()
+            except (ImportError, AttributeError):
+                pass
+
     def update_visualizers(self, dt: float) -> None:
         """Update visualizers without triggering renderer/GUI."""
         if not self._visualizers:

source/isaaclab/test/sim/test_simulation_context.py

@@ -290,6 +290,67 @@ def test_render():
     assert sim.is_playing()
 
 
+@pytest.mark.isaacsim_ci
+def test_render_pumps_app_update_without_visualizer():
+    """Regression test for issue #5052: render() must call app.update() when no visualizer pumps the Kit loop.
+
+    Without this call, replicator render products (used by gym.wrappers.RecordVideo for
+    rgb_array rendering) are never updated, producing black video frames.
+    """
+    from unittest.mock import MagicMock, patch
+
+    cfg = SimulationCfg(dt=0.01)
+    sim = SimulationContext(cfg)
+    sim.reset()
+
+    mock_app = MagicMock()
+    mock_app.is_running.return_value = True
+
+    with patch("omni.kit.app.get_app", return_value=mock_app):
+        sim.render()
+
+    # app.update() must be called when no visualizer pumps the Kit app loop
+    mock_app.update.assert_called_once()
+
+
+@pytest.mark.isaacsim_ci
+def test_render_skips_app_update_when_visualizer_pumps_it():
+    """Regression test: render() must NOT call app.update() when a visualizer already does.
+
+    A visualizer that returns ``pumps_app_update() == True`` (e.g. KitVisualizer) calls
+    ``app.update()`` in its own ``step()``, so ``SimulationContext.render()`` must not
+    call it again to avoid double-rendering.
+    """
+    from unittest.mock import MagicMock, patch
+
+    from isaaclab.visualizers.base_visualizer import BaseVisualizer
+
+    cfg = SimulationCfg(dt=0.01)
+    sim = SimulationContext(cfg)
+    sim.reset()
+
+    # Inject a mock visualizer that pumps the app update
+    mock_viz = MagicMock(spec=BaseVisualizer)
+    mock_viz.pumps_app_update.return_value = True
+    mock_viz.is_closed = False
+    mock_viz.is_running.return_value = True
+    mock_viz.is_rendering_paused.return_value = False
+    mock_viz.is_training_paused.return_value = False
+    mock_viz.get_rendering_dt.return_value = None
+    sim._visualizers = [mock_viz]
+
+    mock_app = MagicMock()
+    mock_app.is_running.return_value = True
+
+    with patch("omni.kit.app.get_app", return_value=mock_app):
+        sim.render()
+
+    # app.update() must NOT be called since the visualizer already pumps it
+    mock_app.update.assert_not_called()
+
+    sim._visualizers = []
+
+
 """
 Stage Operations Tests
 """