List video devices using v4l2 directly, not ffmpeg

Turns out, FFmpeg is annoyingly unreliable when it comes to this. It ignores uvcvideo devices for example

src/platform/camera/v4l2.cpp

@@ -27,6 +27,7 @@
 #include <errno.h>
 #include <sys/ioctl.h>
 #include <linux/videodev2.h>
+#include <dirent.h>
 
 /**
  * Most of this file is adapted from libavdevice's v4l2.c,
@@ -135,3 +136,33 @@ QVector<VideoMode> v4l2::getDeviceModes(QString devName)
 
     return modes;
 }
+
+QVector<QPair<QString, QString>> v4l2::getDeviceList()
+{
+    QVector<QPair<QString, QString>> devices;
+    QVector<QString> deviceFiles;
+
+    DIR *dir = opendir("/dev");
+    if (!dir)
+        return devices;
+
+    dirent* e;
+    while ((e = readdir(dir)))
+        if (!strncmp(e->d_name, "video", 5) || !strncmp(e->d_name, "vbi", 3))
+            deviceFiles += QString("/dev/") + e->d_name;
+    closedir(dir);
+
+    for (QString file : deviceFiles)
+    {
+        int fd = open(file.toStdString().c_str(), O_RDWR);
+        if (fd < 0)
+            continue;
+
+        v4l2_capability caps;
+        ioctl(fd, VIDIOC_QUERYCAP, &caps);
+        close(fd);
+
+        devices += {file, (const char*)caps.card};
+    }
+    return devices;
+}

src/platform/camera/v4l2.h

@@ -31,6 +31,7 @@
 namespace v4l2
 {
     QVector<VideoMode> getDeviceModes(QString devName);
+    QVector<QPair<QString, QString>> getDeviceList();
 }
 
 #endif // V4L2_H

src/video/cameradevice.cpp

@@ -263,6 +263,10 @@ QVector<QPair<QString, QString>> CameraDevice::getDeviceList()
 #ifdef Q_OS_WIN
     else if (iformat->name == QString("dshow"))
         devices += DirectShow::getDeviceList();
+#endif
+#ifdef Q_OS_LINUX
+    else if (iformat->name == QString("video4linux2,v4l2"))
+        devices += v4l2::getDeviceList();
 #endif
     else
         devices += getRawDeviceListGeneric();