feat: implement core functionality for camera preview application
- Add FrameDispatcher for distributing QVideoFrames to subscribers - Implement TelemetryCollector to measure video pipeline performance metrics - Create MainWindow as the main application interface with video rendering - Develop AppMenuBar for camera selection, resolution, and FPS settings - Establish overlay system for displaying telemetry metrics - Set up project structure and configuration files - Add unit tests for FrameDispatcher and TelemetryCollector
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174
app/camera/camera_service.py
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174
app/camera/camera_service.py
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"""Camera Service — manages QCamera lifecycle and frame acquisition."""
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from __future__ import annotations
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import logging
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from PySide6.QtCore import QObject, Signal
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from PySide6.QtMultimedia import (
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QCamera,
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QMediaCaptureSession,
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QVideoFrame,
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QVideoSink,
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)
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from app.camera.camera_enumerator import CameraInfo
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from app.config import DEFAULT_FPS, DEFAULT_HEIGHT, DEFAULT_WIDTH
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logger = logging.getLogger(__name__)
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class CameraService(QObject):
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"""
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Manages camera initialisation, configuration and frame delivery.
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Emits:
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frame_ready(QVideoFrame) — new frame available from the camera
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camera_started() — camera successfully opened and streaming
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camera_stopped() — camera stopped (clean shutdown)
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camera_error(str) — camera error description
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"""
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frame_ready = Signal(QVideoFrame)
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camera_started = Signal()
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camera_stopped = Signal()
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camera_error = Signal(str)
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def __init__(self, parent: QObject | None = None) -> None:
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super().__init__(parent)
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self._camera: QCamera | None = None
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self._session = QMediaCaptureSession(self)
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self._sink = QVideoSink(self)
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self._current_info: CameraInfo | None = None
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self._session.setVideoSink(self._sink)
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self._sink.videoFrameChanged.connect(self._on_frame)
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# ------------------------------------------------------------------
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# Public API
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# ------------------------------------------------------------------
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def start(self, camera_info: CameraInfo) -> None:
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"""Start streaming from the given camera device."""
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self.stop()
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self._current_info = camera_info
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self._camera = QCamera(camera_info.device, self)
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self._camera.errorOccurred.connect(self._on_error)
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self._camera.activeChanged.connect(self._on_active_changed)
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self._session.setCamera(self._camera)
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self._apply_best_format(camera_info)
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self._camera.start()
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logger.info("Camera start requested: %s", camera_info.name)
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def stop(self) -> None:
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"""Stop the current camera."""
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if self._camera is not None:
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self._camera.stop()
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self._camera.errorOccurred.disconnect()
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self._camera.activeChanged.disconnect()
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self._camera = None
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self._current_info = None
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logger.info("Camera stopped")
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def reconnect(self) -> None:
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"""Restart the current camera after an error or disconnect."""
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if self._current_info is not None:
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logger.info("Reconnecting camera: %s", self._current_info.name)
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self.start(self._current_info)
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else:
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logger.warning("Reconnect requested but no camera was previously started")
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def set_resolution(self, width: int, height: int) -> None:
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"""Request a specific resolution. Effective on next start() if camera is active."""
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if self._camera is None:
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return
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self._set_format(width, height, fps=None)
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def set_fps(self, fps: float) -> None:
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"""Request a specific frame rate."""
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if self._camera is None or self._current_info is None:
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return
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# Get current resolution from active format
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fmt = self._camera.cameraFormat()
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res = fmt.resolution()
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self._set_format(res.width(), res.height(), fps=fps)
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@property
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def is_active(self) -> bool:
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return self._camera is not None and self._camera.isActive()
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@property
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def current_camera(self) -> CameraInfo | None:
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return self._current_info
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# ------------------------------------------------------------------
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# Video output accessor for direct QVideoWidget connection
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# ------------------------------------------------------------------
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def video_sink(self) -> QVideoSink:
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"""Return the internal QVideoSink (used by VideoRenderer)."""
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return self._sink
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def capture_session(self) -> QMediaCaptureSession:
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"""Return the capture session (can be connected to QVideoWidget directly)."""
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return self._session
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# ------------------------------------------------------------------
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# Private helpers
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# ------------------------------------------------------------------
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def _apply_best_format(self, info: CameraInfo) -> None:
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"""Pick the best matching format: prefer DEFAULT_WIDTH x DEFAULT_HEIGHT at DEFAULT_FPS."""
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if not info.formats:
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return
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self._set_format(DEFAULT_WIDTH, DEFAULT_HEIGHT, fps=float(DEFAULT_FPS))
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def _set_format(self, width: int, height: int, fps: float | None) -> None:
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if self._camera is None or self._current_info is None:
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return
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best = None
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best_score = -1
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for fmt in self._current_info.device.videoFormats():
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res = fmt.resolution()
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w, h = res.width(), res.height()
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f = fmt.maxFrameRate()
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res_match = int(w == width and h == height) * 1000
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fps_match = int(fps is not None and abs(f - fps) < 1) * 100
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area_score = -(abs(w * h - width * height))
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score = res_match + fps_match + area_score
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if score > best_score:
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best_score = score
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best = fmt
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if best is not None:
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self._camera.setCameraFormat(best)
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res = best.resolution()
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logger.info(
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"Camera format set: %dx%d @ %.1f fps",
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res.width(),
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res.height(),
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best.maxFrameRate(),
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)
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def _on_frame(self, frame: QVideoFrame) -> None:
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if frame.isValid():
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self.frame_ready.emit(frame)
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def _on_error(self, error: QCamera.Error, error_string: str) -> None:
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logger.error("Camera error %s: %s", error, error_string)
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self.camera_error.emit(error_string)
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def _on_active_changed(self, active: bool) -> None:
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if active:
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logger.info("Camera active: %s", self._current_info.name if self._current_info else "?")
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self.camera_started.emit()
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else:
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logger.info("Camera inactive")
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self.camera_stopped.emit()
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