Camera app: Add --video-device arg instead of hardcoding /dev/video0 (project-chip#39552)

* Add app option to get video device path

* Propagate the video device path to camera app

* Apply gemini suggestions for error return & string reuse

* Remove `AppOptions`, add arg to linux options

Author: samadDotDev

examples/camera-app/linux/include/camera-device.h

@@ -66,6 +66,8 @@ static constexpr uint16_t kMaxImageRotation          = 359; // Spec constraint
 
 namespace Camera {
 
+constexpr const char * kDefaultVideoDevicePath = "/dev/video0";
+
 // Camera defined constants for Pan, Tilt, Zoom bounding values
 constexpr int16_t kMinPanValue  = -90;
 constexpr int16_t kMaxPanValue  = 90;
@@ -89,6 +91,8 @@ class CameraDevice : public CameraDeviceInterface, public CameraDeviceInterface:
 
     CameraDeviceInterface::CameraHALInterface & GetCameraHALInterface() override { return *this; }
 
+    void Init();
+
     // HAL interface impl
     CameraError InitializeCameraDevice() override;
 
@@ -267,8 +271,11 @@ class CameraDevice : public CameraDeviceInterface, public CameraDeviceInterface:
 
     std::vector<SnapshotStream> & GetAvailableSnapshotStreams() override { return mSnapshotStreams; }
 
+    void SetVideoDevicePath(const std::string & path) { mVideoDevicePath = path; }
+
 private:
-    int videoDeviceFd = -1;
+    int videoDeviceFd            = -1;
+    std::string mVideoDevicePath = kDefaultVideoDevicePath;
     std::vector<VideoStream> mVideoStreams;       // Vector to hold available video streams
     std::vector<AudioStream> mAudioStreams;       // Vector to hold available audio streams
     std::vector<SnapshotStream> mSnapshotStreams; // Vector to hold available snapshot streams

examples/camera-app/linux/main.cpp

@@ -17,6 +17,7 @@
 
 #include "camera-app.h"
 #include "camera-device.h"
+
 #include <AppMain.h>
 #include <platform/CHIPDeviceConfig.h>
 
@@ -30,6 +31,17 @@ CameraDevice gCameraDevice;
 void ApplicationInit()
 {
     ChipLogProgress(Camera, "Matter Camera Linux App: ApplicationInit()");
+    if (LinuxDeviceOptions::GetInstance().cameraVideoDevice.HasValue())
+    {
+        std::string videoDevicePath = LinuxDeviceOptions::GetInstance().cameraVideoDevice.Value();
+        ChipLogDetail(Camera, "Using video device path from options: %s", videoDevicePath.c_str());
+        gCameraDevice.SetVideoDevicePath(videoDevicePath);
+    }
+    else
+    {
+        ChipLogDetail(Camera, "Using default video device path: %s", Camera::kDefaultVideoDevicePath);
+    }
+    gCameraDevice.Init();
     CameraAppInit(&gCameraDevice);
 }
 

examples/camera-app/linux/src/camera-device.cpp

@@ -315,13 +315,6 @@ GstElement * CreateSnapshotPipelineLibcamerasrc(const SnapshotPipelineConfig & c
 
 CameraDevice::CameraDevice()
 {
-    InitializeCameraDevice();
-
-    InitializeStreams();
-
-    // Initialize WebRTC connnection
-    mWebRTCProviderManager.Init();
-
     // Set the CameraHALInterface in CameraAVStreamManager and CameraAVsettingsUserLevelManager.
     mCameraAVStreamManager.SetCameraDeviceHAL(this);
     mCameraAVSettingsUserLevelManager.SetCameraDeviceHAL(this);
@@ -341,6 +334,13 @@ CameraDevice::~CameraDevice()
     }
 }
 
+void CameraDevice::Init()
+{
+    InitializeCameraDevice();
+    InitializeStreams();
+    mWebRTCProviderManager.Init();
+}
+
 CameraError CameraDevice::InitializeCameraDevice()
 {
     static bool gstreamerInitialized = false;
@@ -351,12 +351,10 @@ CameraError CameraDevice::InitializeCameraDevice()
         gstreamerInitialized = true;
     }
 
-    // TODO: Replace hardcoded device file with device passed in from
-    // camera-app.
-    videoDeviceFd = open("/dev/video0", O_RDWR);
+    videoDeviceFd = open(mVideoDevicePath.c_str(), O_RDWR);
     if (videoDeviceFd == -1)
     {
-        ChipLogError(Camera, "Error opening video device: %s", strerror(errno));
+        ChipLogError(Camera, "Error opening video device: %s at %s", strerror(errno), mVideoDevicePath.c_str());
         return CameraError::ERROR_INIT_FAILED;
     }
 
@@ -629,7 +627,7 @@ CameraError CameraDevice::StartVideoStream(uint16_t streamID)
     // Create Gstreamer video pipeline
     CameraError error = CameraError::SUCCESS;
     GstElement * videoPipeline =
-        CreateVideoPipeline("/dev/video0", it->videoStreamParams.minResolution.width, it->videoStreamParams.minResolution.height,
+        CreateVideoPipeline(mVideoDevicePath, it->videoStreamParams.minResolution.width, it->videoStreamParams.minResolution.height,
                             it->videoStreamParams.minFrameRate, error);
     if (videoPipeline == nullptr)
     {
@@ -804,7 +802,7 @@ CameraError CameraDevice::StartSnapshotStream(uint16_t streamID)
     // Create the GStreamer pipeline
     CameraError error             = CameraError::SUCCESS;
     GstElement * snapshotPipeline = CreateSnapshotPipeline(
-        "/dev/video0", it->snapshotStreamParams.minResolution.width, it->snapshotStreamParams.minResolution.height,
+        mVideoDevicePath, it->snapshotStreamParams.minResolution.width, it->snapshotStreamParams.minResolution.height,
         it->snapshotStreamParams.quality, it->snapshotStreamParams.frameRate, "capture_snapshot.jpg", error);
     if (snapshotPipeline == nullptr)
     {

examples/platform/linux/Options.cpp

@@ -140,6 +140,7 @@ enum
 #endif
 #if ENABLE_CAMERA_SERVER
     kDeviceOption_Camera_DeferredOffer,
+    kDeviceOption_Camera_VideoDevice,
 #endif
     kDeviceOption_VendorName,
     kDeviceOption_ProductName,
@@ -238,6 +239,7 @@ OptionDef sDeviceOptionDefs[] = {
 #endif
 #if ENABLE_CAMERA_SERVER
     { "camera-deferred-offer", kNoArgument, kDeviceOption_Camera_DeferredOffer },
+    { "camera-video-device", kArgumentRequired, kDeviceOption_Camera_VideoDevice },
 #endif
     {}
 };
@@ -443,6 +445,9 @@ const char * sDeviceOptionHelp =
     "\n"
     "  --camera-deferred-offer\n"
     "       Indicates the delayed processing hint of the WebRTC Provider.\n"
+    "\n"
+    "  --camera-video-device <path>\n"
+    "       Path to a V4L2 video capture device (default: /dev/video0).\n"
 #endif
     "\n";
 
@@ -892,6 +897,10 @@ bool HandleOption(const char * aProgram, OptionSet * aOptions, int aIdentifier,
         LinuxDeviceOptions::GetInstance().cameraDeferredOffer = true;
         break;
     }
+    case kDeviceOption_Camera_VideoDevice: {
+        LinuxDeviceOptions::GetInstance().cameraVideoDevice.SetValue(aValue);
+        break;
+    }
 #endif
     default:
         PrintArgError("%s: INTERNAL ERROR: Unhandled option: %s\n", aProgram, aName);

examples/platform/linux/Options.h

@@ -58,6 +58,7 @@ struct LinuxDeviceOptions
     bool mWiFi                 = false;
     bool mThread               = false;
     bool cameraDeferredOffer   = false;
+    chip::Optional<std::string> cameraVideoDevice;
 #if CHIP_DEVICE_CONFIG_ENABLE_WIFIPAF
     bool mWiFiPAF                = false;
     const char * mWiFiPAFExtCmds = nullptr;