updated cap_libv4l.cpp to support CV_CAP_PROP_POS_MSEC, CV_CAP_PROP_POS_FRAMES and CV_CAP_PROP_FPS

modules/videoio/src/cap_libv4l.cpp

@@ -190,6 +190,10 @@ make & enjoy!
     - PlayStation 3 Eye
     - Logitech C920
     - Odroid USB-CAM 720P
+
+17th patch: May 9, 2015, Matt Sandler
+ added supported for CV_CAP_PROP_POS_MSEC, CV_CAP_PROP_POS_FRAMES, CV_CAP_PROP_FPS
+
 */
 
 /*M///////////////////////////////////////////////////////////////////////////////////////
@@ -333,6 +337,11 @@ typedef struct CvCaptureCAM_V4L
    enum v4l2_buf_type type;
    struct v4l2_queryctrl queryctrl;
 
+   struct timeval timestamp;
+
+   /** value set the buffer of V4L*/
+   int sequence;
+
    /* V4L2 control variables */
    v4l2_ctrl_range** v4l2_ctrl_ranges;
    int v4l2_ctrl_count;
@@ -1124,6 +1133,11 @@ static int read_frame_v4l2(CvCaptureCAM_V4L* capture) {
    if (-1 == xioctl (capture->deviceHandle, VIDIOC_QBUF, &buf))
        perror ("VIDIOC_QBUF");
 
+   //set timestamp in capture struct to be timestamp of most recent frame
+   /** where timestamps refer to the instant the field or frame was received by the driver, not the capture time*/
+   capture->timestamp = buf.timestamp;   //printf( "timestamp update done \n");
+   capture->sequence = buf.sequence;
+
    return 1;
 }
 
@@ -1237,16 +1251,16 @@ static int icvGrabFrameCAM_V4L(CvCaptureCAM_V4L* capture) {
    } else
    {
 
-     capture->mmaps[capture->bufferIndex].frame  = capture->bufferIndex;
-     capture->mmaps[capture->bufferIndex].width  = capture->captureWindow.width;
-     capture->mmaps[capture->bufferIndex].height = capture->captureWindow.height;
-     capture->mmaps[capture->bufferIndex].format = capture->imageProperties.palette;
+   capture->mmaps[capture->bufferIndex].frame  = capture->bufferIndex;
+   capture->mmaps[capture->bufferIndex].width  = capture->captureWindow.width;
+   capture->mmaps[capture->bufferIndex].height = capture->captureWindow.height;
+   capture->mmaps[capture->bufferIndex].format = capture->imageProperties.palette;
 
-     if (v4l1_ioctl (capture->deviceHandle, VIDIOCMCAPTURE,
-    &capture->mmaps[capture->bufferIndex]) == -1) {
-   /* capture is on the way, so just exit */
-   return 1;
-     }
+   if (v4l1_ioctl (capture->deviceHandle, VIDIOCMCAPTURE,
+           &capture->mmaps[capture->bufferIndex]) == -1) {
+      /* capture is on the way, so just exit */
+      return 1;
+   }
 
      ++capture->bufferIndex;
      if (capture->bufferIndex == capture->memoryBuffer.frames) {
@@ -1362,6 +1376,36 @@ static double icvGetPropertyCAM_V4L (CvCaptureCAM_V4L* capture,
         }
       }
       return (property_id == CV_CAP_PROP_FRAME_WIDTH)?capture->form.fmt.pix.width:capture->form.fmt.pix.height;
+
+    case CV_CAP_PROP_POS_MSEC:
+        if (capture->FirstCapture) {
+            return 0;
+        } else {
+            //would be maximally numerically stable to cast to convert as bits, but would also be counterintuitive to decode
+            return 1000 * capture->timestamp.tv_sec + ((double) capture->timestamp.tv_usec) / 1000;
+        }
+        break;
+
+    case CV_CAP_PROP_POS_FRAMES:
+        return capture->sequence;
+        break;
+
+    case CV_CAP_PROP_FPS: {
+        struct v4l2_streamparm sp;
+        memset (&sp, 0, sizeof(struct v4l2_streamparm));
+        sp.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+        if (xioctl (capture->deviceHandle, VIDIOC_G_PARM, &sp) < 0){
+            fprintf(stderr, "VIDEOIO ERROR: V4L: Unable to get camera FPS\n");
+            return (double) -1;
+        }
+
+        // this is the captureable, not per say what you'll get..
+        double framesPerSec = sp.parm.capture.timeperframe.denominator / (double)  sp.parm.capture.timeperframe.numerator ;
+        return framesPerSec;
+    }
+    break;
+
+
     case CV_CAP_PROP_MODE:
       return capture->mode;
       break;
@@ -1507,13 +1551,17 @@ static int icvSetVideoSize( CvCaptureCAM_V4L* capture, int w, int h) {
     xioctl (capture->deviceHandle, VIDIOC_S_FMT, &capture->form);
 
     /* try to set framerate to 30 fps */
+
     struct v4l2_streamparm setfps;
     memset (&setfps, 0, sizeof(struct v4l2_streamparm));
+
     setfps.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
     setfps.parm.capture.timeperframe.numerator = 1;
     setfps.parm.capture.timeperframe.denominator = 30;
+
     xioctl (capture->deviceHandle, VIDIOC_S_PARM, &setfps);
 
+
     /* we need to re-initialize some things, like buffers, because the size has
      * changed */
     capture->FirstCapture = 1;