I want to decode the MPEG motion vectors using OpenCV in C++.
Is there any function in OpenCV through which we can get this?
Brightness may not be constant through out the video in my case.
I am referring paper Efficient camera motion characterization for MPEG video indexing
It says use partial decoding to get motion vectors from MPEG-compressed video sequence.
But I am unable to determine how to do this using OpenCV.
How to proceed?
OpenCV uses ffmpeg, v4linux or QuickTime as backend video encoder/decoder. It cannot access internal data or partial decoding results, because it is just a wrapper over other libraries. All it does is to handle frames from the backend and convert them to IplImage or cv::Mat.
If you want to access internal data, you should play with the ffmpeg code.
Related
I am looking for a stabilization technique/algorithm that works with a set of sequential images, but not a video (each image arrives every 1.2s aprox). OpenCV seems to have this stabilization but over video (stabilizer), are there any other classes that I can use to stabilize this set of images? Or, is there a way to make it work with this class?
Cheers and thanks!
I would like to know how OpenCV does to find devices that it can read from?
Can OpenCV only read from usb devices?
I have a video acquisition card (BlackMagic Intensity) and I until now used the blackMagic's SDK to retrieve the stream coming from the input port on the card, and converted it to a cv::Mat that I then use in my code.
But can't I not develop some kind of C++ plugin for OpenCV so that I can use VideoCapture to access my blackMagic stream? wouldn't it be a cleaner way of doing this?
Hope you can help
I am using the Bumblebee2 camera and I am having trouble with acquiring stereo images from it. When I attempt to access the camera using MATLAB, the program crashes.
Does anyone know how I can acquire the stereo images using FlyCapture?
Matlab cannot read the BumbleBee 2 output directly. To do that you'll have to record the stream and process it offline. I wrote a proprietary recorder based on the code samples in the SDK. You can split the left/right images and record each one in a separate video container (e.g. using OpenCV to write a compressed avi file). Later, you can load these images into memory, and use Triclops to compute disparity maps (or alternatively, use OpenCV to run other algorithms, like semi-global block matching).
Flycapture can capture image series or video clips, but you have less control over what you get. I suggest you use the code samples to write a simple recorder, and then load your output into Matlab in standard ways. Consult the Point Grey tech support.
I'm trying to save a video to analyse later with OpenCV algorithms.
I'm using a C++ library of the camera to obtain the frames.
IplImage *iplImageInput = QueryFrame(); //runs every 30 ms
std::vector <cv::Mat> splittedVector;
cv::split(cv::Mat(iplImageInput), splittedVector); //stereo vision camera
// splittedVector buffer is used by the algorithms
So I would like to replace the function "QueryFrame()" with data saved before.
I have already tried some things with cv::videowriter/cv::videocapture but with no luck.
Do you have any hints to eliminate the need for the camera while testing algorithms?
How should I implement a writer and reader to save like 150 frames?
Thanks a lot.
The steps I follow for writing a video file in openCV are as follows:
CvVideoWriter *writer =cvCreateVideoWriter(fileName, Codec ID, frameRate, frameSize); // Create Video Writer
cvWriteFrame(writer, frame); // Write frame
cvReleaseVideoWriter(&writer); // Release video writer
The above code snippet writes at a fixed frame rate. I need to write out variable frame rate videos. The approach I had used earlier with libx264 involved writing individual timestamps to each frame.
So, the question is how do I write timestamps to a frame in openCV - what is the specific API ? More generally, how do I create variable frame rate videos ?
I don't think it is possible to do this with OpenCV directly without modifying the code to give access under the hood. You would need to use a different library like libvlc to do so using the imem to get your raw RGB frames in OpenCV into a file. This link provides an example using imem with raw images loaded from OpenCV. You would just need to change the :sout options to save to the file you want using your preferred codec.