nanokvm: ignore stale frames

Author: mangelajo

packages/jumpstarter-driver-nanokvm/jumpstarter_driver_nanokvm/client.py

@@ -19,14 +19,14 @@ class NanoKVMVideoClient(DriverClient):
     from the NanoKVM device.
     """
 
-    def snapshot(self) -> Image.Image:
+    def snapshot(self, skip_frames: int = 3) -> Image.Image:
         """
         Get a snapshot image from the video stream
 
         Returns:
             PIL Image object of the snapshot
         """
-        input_jpg_data = b64decode(self.call("snapshot"))
+        input_jpg_data = b64decode(self.call("snapshot", skip_frames))
         return Image.open(io.BytesIO(input_jpg_data))
 
     def cli(self):

packages/jumpstarter-driver-nanokvm/jumpstarter_driver_nanokvm/driver.py

@@ -92,16 +92,21 @@ def close(self):
 
     @export
     @with_reauth
-    async def snapshot(self) -> str:
+    async def snapshot(self, skip_frames: int = 3) -> str:
         """
         Take a snapshot from the video stream
 
         Returns:
             Base64 encoded JPEG image data
         """
         client = await self._get_client()
+        frame_count = 0
         async for frame in client.mjpeg_stream():
-            # Get the first frame and return it
+            frame_count += 1
+            # Skip the first frames as it's normally stale
+            if frame_count < skip_frames:
+                continue
+            # Return the second (fresh) frame
             buffer = BytesIO()
             frame.save(buffer, format="JPEG")
             data = buffer.getvalue()

packages/jumpstarter-driver-nanokvm/jumpstarter_driver_nanokvm/driver_test.py

@@ -32,6 +32,10 @@ def mock_nanokvm_client():
         test_image = Image.new("RGB", (640, 480), color="red")
 
         async def mock_stream():
+            # Yield several frames - first ones are buffered/old, later ones are fresh
+            yield test_image
+            yield test_image
+            yield test_image
             yield test_image
 
         mock_client.mjpeg_stream = mock_stream