open v4l2 device with index (#188)

Author: nihui

highgui/src/capture_v4l2.cpp

@@ -61,7 +61,7 @@ class capture_v4l2_impl
     capture_v4l2_impl();
     ~capture_v4l2_impl();
 
-    int open(int width, int height, float fps);
+    int open(int index, int width, int height, float fps);
 
     int start_streaming();
 
@@ -150,18 +150,18 @@ static float fit_score(int cap_width, int cap_height, int width, int height)
     return iou * 20 + ioo * 80;
 }
 
-int capture_v4l2_impl::open(int width, int height, float fps)
+int capture_v4l2_impl::open(int index, int width, int height, float fps)
 {
     int dev_index = -1;
 
-    // enumerate /dev/video%d and find capture + streaming
-    for (int i = 0; i < 64; i++)
+    // try index first
+    while (1)
     {
-        sprintf(devpath, "/dev/video%d", i);
+        sprintf(devpath, "/dev/video%d", index);
 
         fd = ::open(devpath, O_RDWR | O_NONBLOCK, 0);
         if (fd < 0)
-            continue;
+            break;
 
         // query cap
         {
@@ -172,7 +172,7 @@ int capture_v4l2_impl::open(int width, int height, float fps)
             {
                 fprintf(stderr, "%s ioctl VIDIOC_QUERYCAP failed %d %s\n", devpath, errno, strerror(errno));
                 ::close(fd);
-                continue;
+                break;
             }
 
             fprintf(stderr, "   devpath = %s\n", devpath);
@@ -195,21 +195,80 @@ int capture_v4l2_impl::open(int width, int height, float fps)
             {
                 fprintf(stderr, "%s is not V4L2_CAP_VIDEO_CAPTURE or V4L2_CAP_VIDEO_CAPTURE_MPLANE\n", devpath);
                 ::close(fd);
-                continue;
+                break;
             }
 
             if (!(caps.capabilities & V4L2_CAP_STREAMING))
             {
                 fprintf(stderr, "%s is not V4L2_CAP_STREAMING\n", devpath);
                 ::close(fd);
-                continue;
+                break;
             }
         }
 
-        dev_index = i;
+        dev_index = index;
         break;
     }
 
+    if (dev_index == -1)
+    {
+        // enumerate /dev/video%d and find capture + streaming
+        for (int i = 0; i < 64; i++)
+        {
+            sprintf(devpath, "/dev/video%d", i);
+
+            fd = ::open(devpath, O_RDWR | O_NONBLOCK, 0);
+            if (fd < 0)
+                continue;
+
+            // query cap
+            {
+                struct v4l2_capability caps;
+                memset(&caps, 0, sizeof(caps));
+
+                if (ioctl(fd, VIDIOC_QUERYCAP, &caps))
+                {
+                    fprintf(stderr, "%s ioctl VIDIOC_QUERYCAP failed %d %s\n", devpath, errno, strerror(errno));
+                    ::close(fd);
+                    continue;
+                }
+
+                fprintf(stderr, "   devpath = %s\n", devpath);
+                fprintf(stderr, "   driver = %s\n", caps.driver);
+                fprintf(stderr, "   card = %s\n", caps.card);
+                fprintf(stderr, "   bus_info = %s\n", caps.bus_info);
+                fprintf(stderr, "   version = %x\n", caps.version);
+                fprintf(stderr, "   capabilities = %x\n", caps.capabilities);
+                fprintf(stderr, "   device_caps = %x\n", caps.device_caps);
+
+                if (caps.capabilities & V4L2_CAP_VIDEO_CAPTURE)
+                {
+                    buf_type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+                }
+                else if (caps.capabilities & V4L2_CAP_VIDEO_CAPTURE_MPLANE)
+                {
+                    buf_type = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;
+                }
+                else
+                {
+                    fprintf(stderr, "%s is not V4L2_CAP_VIDEO_CAPTURE or V4L2_CAP_VIDEO_CAPTURE_MPLANE\n", devpath);
+                    ::close(fd);
+                    continue;
+                }
+
+                if (!(caps.capabilities & V4L2_CAP_STREAMING))
+                {
+                    fprintf(stderr, "%s is not V4L2_CAP_STREAMING\n", devpath);
+                    ::close(fd);
+                    continue;
+                }
+            }
+
+            dev_index = i;
+            break;
+        }
+    }
+
     if (dev_index == -1)
     {
         fprintf(stderr, "cannot find v4l device with VIDEO_CAPTURE and STREAMING\n");
@@ -916,9 +975,9 @@ capture_v4l2::~capture_v4l2()
     delete d;
 }
 
-int capture_v4l2::open(int width, int height, float fps)
+int capture_v4l2::open(int index, int width, int height, float fps)
 {
-    return d->open(width, height, fps);
+    return d->open(index, width, height, fps);
 }
 
 int capture_v4l2::get_width() const

highgui/src/capture_v4l2.h

@@ -30,7 +30,7 @@ class capture_v4l2
     capture_v4l2();
     ~capture_v4l2();
 
-    int open(int width = 640, int height = 480, float fps = 30);
+    int open(int index, int width = 640, int height = 480, float fps = 30);
 
     int get_width() const;
     int get_height() const;

highgui/src/videocapture.cpp

@@ -158,7 +158,7 @@ bool VideoCapture::open(int index)
 #if defined __linux__
     if (capture_v4l2::supported())
     {
-        int ret = d->cap_v4l2.open(d->width, d->height, d->fps);
+        int ret = d->cap_v4l2.open(index, d->width, d->height, d->fps);
         if (ret == 0)
         {
             d->width = d->cap_v4l2.get_width();