Video editing

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Original author	Amir Hassan (kallaballa) amir@.nosp@m.viel.nosp@m.-zu.o.nosp@m.rg
Compatibility	OpenCV >= 4.7

Render text on top of a video

Through adding a source and a sink v4d becomes capable of video editing. Reads a video, renders text on top and writes the result. Note: Reading and writing of video-data is multi-threaded in the background for performance reasons.

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#include <opencv2/v4d/v4d.hpp>
 
using namespace cv;
using namespace cv::v4d;
 
int main(int argc, char** argv) {
    Ptr<V4D> window = V4D::make(960, 960, "Video Editing", false, false, 0);
 
    //In case of WebAssembly
    CV_UNUSED(argc);
    CV_UNUSED(argv);
 
    string hv = "Hello Video!";
 
#ifndef __EMSCRIPTEN__
    //Make the video source
    Source src = makeCaptureSource(argv[1]);
 
    //Make the video sink
    Sink sink = makeWriterSink(argv[2], src.fps(), cv::Size(960, 960));
    //Attach source and sink
    window->setSource(src);
    window->setSink(sink);
#else
    //Make a webcam Source
    Source src = makeCaptureSource(960, 960, window);
    //Attach webcam source
    window->setSource(src);
#endif
 
    window->run([hv](Ptr<V4D> win) {
        //Capture video from the source
        if(!win->capture())
            return false; //end of input video
 
        //Render on top of the video
        win->nvg([hv](const Size& sz) {
            using namespace cv::v4d::nvg;
 
            fontSize(40.0f);
            fontFace("sans-bold");
            fillColor(Scalar(255, 0, 0, 255));
            textAlign(NVG_ALIGN_CENTER | NVG_ALIGN_TOP);
            text(sz.width / 2.0, sz.height / 2.0, hv.c_str(), hv.c_str() + hv.size());
        });
 
        //Write video to the sink (do nothing in case of WebAssembly)
        win->write();
 
        return win->display();
    });
}