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;
 
class VideoEditingPlan : public Plan {
    cv::UMat frame_;
    const string hv_ = "Hello Video!";
    cv::Size fbSz_;
public:
    void setup(Ptr<V4D> win) override {
        fbSz_ = win->fbSize();
    }
 
    void infer(Ptr<V4D> win) override {
        //Capture video from the source
        win->capture();
 
        //Render on top of the video
        win->nvg([](const Size& sz, const string& str) {
            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, str.c_str(), str.c_str() + str.size());
        }, fbSz_, hv_);
 
        //Write video to the sink (do nothing in case of WebAssembly)
        win->write();
    }
};
 
int main(int argc, char** argv) {
    //In case of WebAssembly
    CV_UNUSED(argc);
    CV_UNUSED(argv);
 
    Ptr<V4D> window = V4D::make(960, 960, "Video Editing");
 
#ifndef __EMSCRIPTEN__
    //Make the video source
    auto src = makeCaptureSource(window, argv[1]);
 
    //Make the video sink
    auto sink = makeWriterSink(window, argv[2], src->fps(), cv::Size(960, 960));
    //Attach source and sink
    window->setSource(src);
    window->setSink(sink);
#else
    //Make a webcam Source
    auto src = makeCaptureSource(window);
    //Attach webcam source
    window->setSource(src);
#endif
 
    window->run<VideoEditingPlan>(0);
}