Question

How can I retrieve the current frame number of a video using OpenCV? Does OpenCV have any built-in function for getting the current frame or I have to do it manually?

Answer 1

You can use the "get" method of your capture object like below :

capture.get(CV_CAP_PROP_POS_FRAMES); // retrieves the current frame number

and also :

capture.get(CV_CAP_PROP_FRAME_COUNT); // returns the number of total frames 

Btw, these methods return a double value.

You can also use cvGetCaptureProperty method (if you use old C interface).

cvGetCaptureProperty(CvCapture* capture,int property_id);

property_id options are below with definitions:

CV_CAP_PROP_POS_MSEC 0

CV_CAP_PROP_POS_FRAME 1

CV_CAP_PROP_POS_AVI_RATIO 2

CV_CAP_PROP_FRAME_WIDTH 3

CV_CAP_PROP_FRAME_HEIGHT 4

CV_CAP_PROP_FPS 5

CV_CAP_PROP_FOURCC 6

CV_CAP_PROP_FRAME_COUNT 7

• POS_MSEC is the current position in a video file, measured in
  milliseconds.
• POS_FRAME is the position of current frame in video (like 55th frame of video).
• POS_AVI_RATIO is the current position given as a number between 0 and 1
  (this is actually quite useful when you want to position a trackbar
  to allow folks to navigate around your video).
• FRAME_WIDTH and FRAME_HEIGHT are the dimensions of the individual
  frames of the video to be read (or to be captured at the camera’s
  current settings).
• FPS is specific to video files and indicates the number of frames
  per second at which the video was captured. You will need to know
  this if you want to play back your video and have it come out at the
  right speed.
• FOURCC is the four-character code for the compression codec to be
  used for the video you are currently reading.
• FRAME_COUNT should be the total number of frames in video, but
  this figure is not entirely reliable.

(from Learning OpenCV book )