OpenCV with Network Cameras

Question

I'm using openCV 1.1pre1 under Windows. I have a network camera and I need to grab frames from openCV. That camera can stream a standard mpeg4 stream over RTSP or mjpeg over http. I've seen many threads talking about using ffmpeg with openCV but I cannot make it work.

How I can grab frames from an IP camera with openCV?

Thanks

Andrea

Answer 1

Use ffmpeglib to connect to the stream.

These functions may be useful. But take a look in the docs

av_open_input_stream(...);
av_find_stream_info(...);
avcodec_find_decoder(...);
avcodec_open(...);
avcodec_alloc_frame(...);

You would need a little algo to get a complete frame, which is available here

http://www.dranger.com/ffmpeg/tutorial01.html

Once you get a frame you could copy the video data (for each plane if needed) into a IplImage which is an OpenCV image object.

You can create an IplImage using something like...

IplImage *p_gray_image = cvCreateImage(size, IPL_DEPTH_8U, 1);

Once you have an IplImage, you could perform all sorts of image operations available in the OpenCV lib

Answer 2

OpenCV can be compiled with FFMPEG support. From ./configure --help:

--with-ffmpeg     use ffmpeg libraries (see LICENSE) [automatic]

You can then use *cvCreateFileCapture_FFMPEG* to create a CvCapture with e.g. the URL of the camera's MJPG stream.

I use this to grab frames from an AXIS camera:

CvCapture *capture = 
    cvCreateFileCapture_FFMPEG("http://axis-cam/mjpg/video.mjpg?resolution=640x480&req_fps=10&.mjpg");

Answer 3

I just do it like this:

CvCapture *capture = cvCreateFileCapture("rtsp://camera-address");

Also make sure this dll is available at runtime else cvCreateFileCapture will return NULL

opencv_ffmpeg200d.dll

The camera needs to allow unauthenticated access too, usually set via its web interface. MJPEG format worked via rtsp but MPEG4 didn't.

hth

Si