diff --git a/duck_preview/__init__.py b/duck_preview/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/duck_preview/__main__.py b/duck_preview/__main__.py
new file mode 100644
index 0000000..35c33ad
--- /dev/null
+++ b/duck_preview/__main__.py
@@ -0,0 +1,3 @@
+from duck_preview.app import main
+
+main()
diff --git a/duck_preview/app.py b/duck_preview/app.py
new file mode 100644
index 0000000..dac8e17
--- /dev/null
+++ b/duck_preview/app.py
@@ -0,0 +1,42 @@
+from __future__ import annotations
+
+import sys
+
+from PySide6.QtCore import QTimer
+from PySide6.QtWidgets import QApplication
+
+from duck_preview.camera.service import CameraService
+from duck_preview.dispatcher.frame_dispatcher import FrameDispatcher
+from duck_preview.main_window import MainWindow
+from duck_preview.rendering.overlay import OverlayWidget
+from duck_preview.rendering.video_widget import VideoWidget
+from duck_preview.telemetry.collector import TelemetryCollector
+
+
+def main() -> None:
+    app = QApplication(sys.argv)
+    app.setApplicationName("Duck Preview")
+
+    camera = CameraService()
+    dispatcher = FrameDispatcher()
+    telemetry = TelemetryCollector()
+    video_widget = VideoWidget()
+    overlay = OverlayWidget()
+
+    camera.sink.videoFrameChanged.connect(dispatcher.on_frame)
+
+    dispatcher.subscribe(telemetry.on_frame)
+    dispatcher.subscribe(video_widget.on_frame)
+
+    window = MainWindow(camera, video_widget, overlay)
+
+    metrics_timer = QTimer()
+    metrics_timer.timeout.connect(lambda: overlay.set_metrics(telemetry.metrics()))
+    metrics_timer.start(200)
+
+    window.show()
+    sys.exit(app.exec())
+
+
+if __name__ == "__main__":
+    main()
diff --git a/duck_preview/camera/__init__.py b/duck_preview/camera/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/duck_preview/camera/service.py b/duck_preview/camera/service.py
new file mode 100644
index 0000000..2b31eb3
--- /dev/null
+++ b/duck_preview/camera/service.py
@@ -0,0 +1,58 @@
+from __future__ import annotations
+
+from PySide6.QtCore import QObject, Signal
+from PySide6.QtMultimedia import (
+    QCamera,
+    QCameraDevice,
+    QCameraFormat,
+    QMediaCaptureSession,
+    QMediaDevices,
+    QVideoSink,
+)
+
+
+class CameraService(QObject):
+    error_occurred = Signal(str)
+
+    def __init__(self, parent: QObject | None = None) -> None:
+        super().__init__(parent)
+        self._session = QMediaCaptureSession()
+        self._sink = QVideoSink()
+        self._session.setVideoOutput(self._sink)
+        self._camera: QCamera | None = None
+
+    @property
+    def sink(self) -> QVideoSink:
+        return self._sink
+
+    @property
+    def session(self) -> QMediaCaptureSession:
+        return self._session
+
+    @staticmethod
+    def available_cameras() -> list[QCameraDevice]:
+        return QMediaDevices.videoInputs()
+
+    def is_active(self) -> bool:
+        return self._camera is not None and self._camera.isActive()
+
+    def start(self, device: QCameraDevice) -> None:
+        self.stop()
+        self._camera = QCamera(device, self)
+        self._camera.errorOccurred.connect(self._on_error)
+        self._session.setCamera(self._camera)
+        self._camera.start()
+
+    def stop(self) -> None:
+        if self._camera is not None:
+            self._camera.stop()
+            self._session.setCamera(None)
+            self._camera.deleteLater()
+            self._camera = None
+
+    def set_camera_format(self, fmt: QCameraFormat) -> None:
+        if self._camera is not None:
+            self._camera.setCameraFormat(fmt)
+
+    def _on_error(self, error: QCamera.Error, error_string: str) -> None:
+        self.error_occurred.emit(error_string)
diff --git a/duck_preview/dispatcher/__init__.py b/duck_preview/dispatcher/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/duck_preview/dispatcher/frame_dispatcher.py b/duck_preview/dispatcher/frame_dispatcher.py
new file mode 100644
index 0000000..02064ea
--- /dev/null
+++ b/duck_preview/dispatcher/frame_dispatcher.py
@@ -0,0 +1,22 @@
+from __future__ import annotations
+
+from collections.abc import Callable
+
+from PySide6.QtCore import QObject
+from PySide6.QtMultimedia import QVideoFrame
+
+
+class FrameDispatcher(QObject):
+    def __init__(self, parent: QObject | None = None) -> None:
+        super().__init__(parent)
+        self._subscribers: list[Callable[[QVideoFrame], None]] = []
+
+    def subscribe(self, callback: Callable[[QVideoFrame], None]) -> None:
+        self._subscribers.append(callback)
+
+    def unsubscribe(self, callback: Callable[[QVideoFrame], None]) -> None:
+        self._subscribers.remove(callback)
+
+    def on_frame(self, frame: QVideoFrame) -> None:
+        for cb in self._subscribers:
+            cb(frame)
diff --git a/duck_preview/main_window.py b/duck_preview/main_window.py
new file mode 100644
index 0000000..2712e9b
--- /dev/null
+++ b/duck_preview/main_window.py
@@ -0,0 +1,118 @@
+from __future__ import annotations
+
+from PySide6.QtGui import QAction, QCloseEvent
+from PySide6.QtMultimedia import QCameraDevice, QMediaDevices
+from PySide6.QtWidgets import QGridLayout, QMainWindow, QWidget
+
+from duck_preview.camera.service import CameraService
+from duck_preview.rendering.overlay import OverlayWidget
+from duck_preview.rendering.video_widget import VideoWidget
+
+
+class MainWindow(QMainWindow):
+    def __init__(
+        self,
+        camera_service: CameraService,
+        video_widget: VideoWidget,
+        overlay_widget: OverlayWidget,
+        parent: QWidget | None = None,
+    ) -> None:
+        super().__init__(parent)
+        self._camera = camera_service
+        self._video_widget = video_widget
+        self._overlay = overlay_widget
+        self._media_devices = QMediaDevices()
+
+        self.setWindowTitle("Duck Preview")
+        self.resize(1280, 720)
+
+        central = QWidget()
+        self.setCentralWidget(central)
+        layout = QGridLayout(central)
+        layout.setContentsMargins(0, 0, 0, 0)
+        layout.setSpacing(0)
+        layout.addWidget(video_widget, 0, 0)
+        layout.addWidget(overlay_widget, 0, 0)
+
+        self._setup_menus()
+
+        self._media_devices.videoInputsChanged.connect(self._rebuild_camera_menu)
+
+    def _setup_menus(self) -> None:
+        menu_bar = self.menuBar()
+
+        self._camera_menu = menu_bar.addMenu("Camera")
+        self._rebuild_camera_menu()
+
+        self._resolution_menu = menu_bar.addMenu("Resolution")
+        self._resolution_menu.setEnabled(False)
+
+        self._fps_menu = menu_bar.addMenu("FPS")
+        self._fps_menu.setEnabled(False)
+
+        debug_menu = menu_bar.addMenu("Debug")
+        toggle_overlay = QAction("Show Metrics", self)
+        toggle_overlay.setCheckable(True)
+        toggle_overlay.setChecked(True)
+        toggle_overlay.triggered.connect(self._overlay.set_visible)
+        debug_menu.addAction(toggle_overlay)
+
+    def _rebuild_camera_menu(self) -> None:
+        self._camera_menu.clear()
+        cameras = CameraService.available_cameras()
+        for device in cameras:
+            action = QAction(device.description(), self)
+            action.triggered.connect(lambda checked, d=device: self._on_camera_selected(d))
+            self._camera_menu.addAction(action)
+        if not cameras:
+            action = QAction("No cameras detected", self)
+            action.setEnabled(False)
+            self._camera_menu.addAction(action)
+
+    def _on_camera_selected(self, device: QCameraDevice) -> None:
+        self._camera.start(device)
+        self._rebuild_resolution_menu(device)
+
+    def _rebuild_resolution_menu(self, device: QCameraDevice) -> None:
+        self._resolution_menu.clear()
+        self._resolution_menu.setEnabled(True)
+        formats = device.videoFormats()
+        seen: set[tuple[int, int]] = set()
+        for fmt in formats:
+            res = fmt.resolution()
+            key = (res.width(), res.height())
+            if key not in seen:
+                seen.add(key)
+                action = QAction(f"{res.width()}x{res.height()}", self)
+                action.triggered.connect(
+                    lambda checked, d=device, w=res.width(), h=res.height(): (
+                        self._on_resolution_selected(d, w, h)
+                    )
+                )
+                self._resolution_menu.addAction(action)
+
+    def _on_resolution_selected(self, device: QCameraDevice, width: int, height: int) -> None:
+        self._rebuild_fps_menu(device, width, height)
+
+    def _rebuild_fps_menu(self, device: QCameraDevice, width: int, height: int) -> None:
+        self._fps_menu.clear()
+        self._fps_menu.setEnabled(True)
+        formats = device.videoFormats()
+        seen_labels: set[str] = set()
+        for fmt in formats:
+            res = fmt.resolution()
+            if res.width() == width and res.height() == height:
+                min_fps = round(fmt.minFrameRate())
+                max_fps = round(fmt.maxFrameRate())
+                label = f"{max_fps} FPS" if min_fps == max_fps else f"{min_fps}-{max_fps} FPS"
+                if label not in seen_labels:
+                    seen_labels.add(label)
+                    action = QAction(label, self)
+                    action.triggered.connect(
+                        lambda checked, f=fmt: self._camera.set_camera_format(f)
+                    )
+                    self._fps_menu.addAction(action)
+
+    def closeEvent(self, event: QCloseEvent) -> None:  # noqa: N802
+        self._camera.stop()
+        super().closeEvent(event)
diff --git a/duck_preview/rendering/__init__.py b/duck_preview/rendering/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/duck_preview/rendering/overlay.py b/duck_preview/rendering/overlay.py
new file mode 100644
index 0000000..96fff05
--- /dev/null
+++ b/duck_preview/rendering/overlay.py
@@ -0,0 +1,49 @@
+from __future__ import annotations
+
+from PySide6.QtCore import Qt
+from PySide6.QtGui import QColor, QFont, QFontMetrics, QPainter
+from PySide6.QtWidgets import QWidget
+
+
+class OverlayWidget(QWidget):
+    def __init__(self, parent: QWidget | None = None) -> None:
+        super().__init__(parent)
+        self.setAttribute(Qt.WA_TransparentForMouseEvents)
+        self.setAttribute(Qt.WA_NoSystemBackground)
+        self._visible = True
+        self._metrics: dict[str, float | int] = {}
+
+    def set_visible(self, visible: bool) -> None:
+        self._visible = visible
+        self.update()
+
+    def set_metrics(self, metrics: dict[str, float | int]) -> None:
+        self._metrics = metrics
+        self.update()
+
+    def paintEvent(self, event) -> None:  # noqa: N802
+        if not self._visible or not self._metrics:
+            return
+
+        lines = [
+            f"FPS:     {self._metrics.get('fps', 0):>7}",
+            f"Frame:   {self._metrics.get('frame_time_ms', 0):>7.1f} ms",
+            f"Frames:  {self._metrics.get('frame_count', 0):>7}",
+        ]
+
+        painter = QPainter(self)
+        painter.setRenderHint(QPainter.TextAntialiasing)
+
+        font = QFont("Consolas", 11)
+        painter.setFont(font)
+        fm = QFontMetrics(font)
+
+        text_width = max(fm.horizontalAdvance(line) for line in lines) + 24
+        text_height = len(lines) * (fm.height() + 6) + 12
+
+        painter.fillRect(8, 8, text_width, text_height, QColor(0, 0, 0, 160))
+
+        painter.setPen(QColor(0, 255, 0))
+        for i, line in enumerate(lines):
+            y = 22 + i * (fm.height() + 6)
+            painter.drawText(16, y, line)
diff --git a/duck_preview/rendering/video_widget.py b/duck_preview/rendering/video_widget.py
new file mode 100644
index 0000000..f659c7c
--- /dev/null
+++ b/duck_preview/rendering/video_widget.py
@@ -0,0 +1,39 @@
+from __future__ import annotations
+
+from PySide6.QtCore import Qt
+from PySide6.QtGui import QColor, QImage, QPainter
+from PySide6.QtMultimedia import QVideoFrame
+from PySide6.QtWidgets import QWidget
+
+
+class VideoWidget(QWidget):
+    def __init__(self, parent: QWidget | None = None) -> None:
+        super().__init__(parent)
+        self._frame: QImage | None = None
+        self.setAttribute(Qt.WA_OpaquePaintEvent)
+        self.setMinimumSize(320, 240)
+
+    def on_frame(self, frame: QVideoFrame) -> None:
+        image = frame.toImage()
+        if not image.isNull():
+            self._frame = image
+            self.update()
+
+    def paintEvent(self, event) -> None:  # noqa: N802
+        painter = QPainter(self)
+        painter.setRenderHint(QPainter.SmoothPixmapTransform)
+
+        if self._frame is not None:
+            painter.fillRect(self.rect(), QColor(0, 0, 0))
+            scaled = self._frame.scaled(
+                self.size(),
+                Qt.KeepAspectRatio,
+                Qt.SmoothTransformation,
+            )
+            x = (self.width() - scaled.width()) // 2
+            y = (self.height() - scaled.height()) // 2
+            painter.drawImage(x, y, scaled)
+        else:
+            painter.fillRect(self.rect(), QColor(20, 20, 20))
+            painter.setPen(QColor(100, 100, 100))
+            painter.drawText(self.rect(), Qt.AlignCenter, "No camera feed")
diff --git a/duck_preview/telemetry/__init__.py b/duck_preview/telemetry/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/duck_preview/telemetry/collector.py b/duck_preview/telemetry/collector.py
new file mode 100644
index 0000000..fd698aa
--- /dev/null
+++ b/duck_preview/telemetry/collector.py
@@ -0,0 +1,39 @@
+from __future__ import annotations
+
+import time
+from collections import deque
+
+from PySide6.QtCore import QObject
+from PySide6.QtMultimedia import QVideoFrame
+
+
+class TelemetryCollector(QObject):
+    def __init__(self, parent: QObject | None = None) -> None:
+        super().__init__(parent)
+        self._timestamps: deque[float] = deque(maxlen=500)
+
+    def on_frame(self, frame: QVideoFrame) -> None:
+        self._timestamps.append(time.perf_counter())
+
+    def metrics(self) -> dict[str, float | int]:
+        if not self._timestamps:
+            return {"fps": 0, "frame_time_ms": 0.0, "frame_count": 0}
+
+        now = time.perf_counter()
+        cutoff = now - 1.0
+        recent = [t for t in self._timestamps if t >= cutoff]
+        fps = len(recent)
+
+        frame_time_ms = 0.0
+        if len(self._timestamps) >= 2:
+            diffs = [
+                self._timestamps[i] - self._timestamps[i - 1]
+                for i in range(1, len(self._timestamps))
+            ]
+            frame_time_ms = (sum(diffs) / len(diffs)) * 1000 if diffs else 0.0
+
+        return {
+            "fps": fps,
+            "frame_time_ms": round(frame_time_ms, 2),
+            "frame_count": len(self._timestamps),
+        }
diff --git a/notes/01-mvp-plan.md b/notes/01-mvp-plan.md
new file mode 100644
index 0000000..2f5a6de
--- /dev/null
+++ b/notes/01-mvp-plan.md
@@ -0,0 +1,150 @@
+# MVP Implementation Plan — Duck Preview
+
+## Stack
+
+- **Language:** Python 3.12
+- **GUI/Framework:** PySide6 6.11 (QtMultimedia + QtWidgets)
+- **Camera backend:** QCamera + QMediaCaptureSession + QVideoSink (native GPU)
+- **Rendering:** QWidget (paintEvent) z QPainter — manual render z QVideoFrame → QImage
+- **Testing:** pytest
+- **Linting/Formatting:** ruff
+
+## Architecture
+
+```
+CameraService
+  └─ QVideoSink.videoFrame ──→ FrameDispatcher.on_frame
+                                   ├─ VideoWidget.on_frame  (render klatki)
+                                   ├─ TelemetryCollector.on_frame  (timestamp)
+                                   └─ [Future AI subscribers]
+
+TelemetryCollector.metrics() ──→ OverlayWidget.set_metrics()
+                                  (polled co 200ms przez QTimer w app.py)
+```
+
+## Kolejność implementacji
+
+### 0. Project scaffolding
+`pyproject.toml` — projekt, zależność PySide6, entry point, ruff config, pytest
+`duck_preview/__init__.py`, `__main__.py` — entry point `python -m duck_preview`
+Podkatalogi: `camera/`, `dispatcher/`, `rendering/`, `telemetry/`
+
+### 1. CameraService (`camera/service.py`)
+- Wrapper na `QCamera` + `QMediaCaptureSession` + `QVideoSink`
+- `available_cameras()` — static, zwraca listę `QCameraDevice` z `QMediaDevices`
+- `start(device)` / `stop()` — zarządzanie cyklem życia kamery
+- `set_camera_format(fmt)` — zmiana rozdzielczości/FPS
+- `sink` property — QVideoSink do podpięcia dispatchera
+- `error_occurred` Signal — propagacja błędów kamery
+
+### 2. FrameDispatcher (`dispatcher/frame_dispatcher.py`)
+- Prosty pub/sub: `subscribe(cb)` / `unsubscribe(cb)`
+- `on_frame(frame)` — wołany z sygnału QVideoSink, iteruje wszystkich subskrybentów
+- Frame dropping: na razie brak (wszystkie callbacki szybkie)
+
+### 3. TelemetryCollector (`telemetry/collector.py`)
+- Subskrybent dispatchera
+- Zbiera timestampy (`deque`, maxlen=500)
+- `metrics()` → dict: fps (klatki z ostatniej sekundy), frame_time_ms (średnia delta między klatkami), frame_count
+- Brak CPU usage (out of scope na MVP)
+
+### 4. VideoWidget (`rendering/video_widget.py`)
+- `QWidget` z `WA_OpaquePaintEvent`
+- `on_frame(frame)` — `frame.toImage()` → zapis QImage → `update()`
+- `paintEvent` — skalowanie z zachowaniem proporcji, centrowanie, letterboxing
+- Brak klatek → wyświetla "No camera feed"
+
+### 5. OverlayWidget (`rendering/overlay.py`)
+- Przezroczysty QWidget (`WA_TransparentForMouseEvents`)
+- Nakładka na video, rysuje tekst metryk (FPS, frame time, frame count)
+- Semi-transparentne tło, zielona czcionka Consolas
+- Toggle widoczności przez menu Debug
+
+### 6. MainWindow (`main_window.py`)
+- `QMainWindow` z menu barem:
+  - **Camera** — lista dostępnych kamer (dynamiczna, reaguje na `videoInputsChanged`)
+  - **Resolution** — dostępne rozdzielczości dla wybranej kamery
+  - **FPS** — dostępne FPS dla wybranej rozdzielczości
+  - **Debug** — toggle nakładki
+- Central widget: GridLayout z VideoWidget + OverlayWidget (stacked)
+
+### 7. App (`app.py`)
+- `main()` — tworzy QApplication, instancjonuje i łączy zależności (ręczne DI)
+- Wire: camera.sink → dispatcher.on_frame
+- Wire: dispatcher → telemetry.on_frame, video_widget.on_frame
+- QTimer 200ms: telemetry.metrics() → overlay.set_metrics()
+- `__main__.py` → `from duck_preview.app import main; main()`
+
+---
+
+## DI Wiring (ręczne, w app.py)
+
+```
+app = QApplication(sys.argv)
+
+camera = CameraService()
+dispatcher = FrameDispatcher()
+telemetry = TelemetryCollector()
+video_widget = VideoWidget()
+overlay = OverlayWidget()
+
+camera.sink.videoFrame.connect(dispatcher.on_frame)
+
+dispatcher.subscribe(telemetry.on_frame)
+dispatcher.subscribe(video_widget.on_frame)
+
+window = MainWindow(camera, video_widget, overlay)
+
+# Poll telemetry co 200ms → overlay
+metrics_timer = QTimer()
+metrics_timer.timeout.connect(lambda: overlay.set_metrics(telemetry.metrics()))
+metrics_timer.start(200)
+
+window.show()
+app.exec()
+```
+
+---
+
+## Struktura plików
+
+```
+duck-preview/
+├── pyproject.toml
+├── notes/
+│   ├── 01-mvp-preview.md
+│   └── 01-mvp-plan.md
+├── duck_preview/
+│   ├── __init__.py
+│   ├── __main__.py
+│   ├── app.py
+│   ├── main_window.py
+│   ├── camera/
+│   │   ├── __init__.py
+│   │   └── service.py
+│   ├── dispatcher/
+│   │   ├── __init__.py
+│   │   └── frame_dispatcher.py
+│   ├── rendering/
+│   │   ├── __init__.py
+│   │   ├── video_widget.py
+│   │   └── overlay.py
+│   └── telemetry/
+│       ├── __init__.py
+│       └── collector.py
+└── tests/
+    ├── __init__.py
+    ├── test_dispatcher.py
+    └── test_collector.py
+```
+
+---
+
+## Edge cases / uwagi
+
+- Brak kamer → menu Camera pokazuje "No cameras detected"
+- Brak klatek → VideoWidget pokazuje ciemne tło + napis
+- Błąd kamery → CameraService emituje `error_occurred` (na razie tylko log)
+- Zamknięcie okna → `closeEvent` → `camera.stop()`
+- QVideoFrame.toImage() kopiuje dane — akceptowalne dla MVP
+- Wszystkie obiekty żyją w main thread — brak problemów z threadingiem
diff --git a/pyproject.toml b/pyproject.toml
new file mode 100644
index 0000000..9080be0
--- /dev/null
+++ b/pyproject.toml
@@ -0,0 +1,21 @@
+[project]
+name = "duck-preview"
+version = "0.1.0"
+description = "Realtime camera preview application with performance monitoring"
+requires-python = ">=3.12"
+dependencies = [
+    "PySide6>=6.11",
+]
+
+[project.scripts]
+duck-preview = "duck_preview.app:main"
+
+[tool.ruff]
+target-version = "py312"
+line-length = 100
+
+[tool.ruff.lint]
+select = ["E", "F", "I", "N", "W"]
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]
diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/test_collector.py b/tests/test_collector.py
new file mode 100644
index 0000000..c42e760
--- /dev/null
+++ b/tests/test_collector.py
@@ -0,0 +1,22 @@
+import time
+from unittest.mock import MagicMock
+
+from duck_preview.telemetry.collector import TelemetryCollector
+
+
+def test_metrics_empty():
+    collector = TelemetryCollector()
+    metrics = collector.metrics()
+    assert metrics == {"fps": 0, "frame_time_ms": 0.0, "frame_count": 0}
+
+
+def test_metrics_after_frames():
+    collector = TelemetryCollector()
+    mock = MagicMock()
+    for _ in range(30):
+        collector.on_frame(mock)
+        time.sleep(0.002)
+
+    metrics = collector.metrics()
+    assert metrics["frame_count"] >= 30
+    assert metrics["frame_time_ms"] > 0
diff --git a/tests/test_dispatcher.py b/tests/test_dispatcher.py
new file mode 100644
index 0000000..ef5288c
--- /dev/null
+++ b/tests/test_dispatcher.py
@@ -0,0 +1,47 @@
+from duck_preview.dispatcher.frame_dispatcher import FrameDispatcher
+
+
+def test_subscribe_notified():
+    dispatcher = FrameDispatcher()
+    received = []
+
+    def cb(frame):
+        received.append(frame)
+
+    dispatcher.subscribe(cb)
+    dispatcher.on_frame("test")
+
+    assert received == ["test"]
+
+
+def test_unsubscribe_not_notified():
+    dispatcher = FrameDispatcher()
+    received = []
+
+    def cb(frame):
+        received.append(frame)
+
+    dispatcher.subscribe(cb)
+    dispatcher.unsubscribe(cb)
+    dispatcher.on_frame("test")
+
+    assert received == []
+
+
+def test_multiple_subscribers():
+    dispatcher = FrameDispatcher()
+    received_1 = []
+    received_2 = []
+
+    def cb1(frame):
+        received_1.append(frame)
+
+    def cb2(frame):
+        received_2.append(frame)
+
+    dispatcher.subscribe(cb1)
+    dispatcher.subscribe(cb2)
+    dispatcher.on_frame("test")
+
+    assert received_1 == ["test"]
+    assert received_2 == ["test"]