stream udp video

video_stream.cpp

// File: video_stream.cpp
// sudo apt-get install libgstreamer1.0-dev libgstreamer-plugins-base1.0-dev
// g++ video_stream.cpp -o video_stream $(pkg-config --cflags --libs opencv4 gstreamer-1.0 gstreamer-app-1.0)

#include <iostream>
#include <gst/gst.h>
#include <gst/app/gstappsink.h>
#include <opencv2/opencv.hpp>

int main(int argc, char* argv[]) {
    // Build the GStreamer pipeline string.
    // NOTE: We removed "h264parse" from the pipeline.
    std::string pipelineStr =
        "udpsrc port=5600 ! application/x-rtp, payload=96 "
        "! rtph264depay ! avdec_h264 "
        "! videoconvert ! video/x-raw,format=(string)BGR "
        "! appsink name=mysink emit-signals=true sync=false max-buffers=2 drop=true";

    // Initialize GStreamer.
    gst_init(&argc, &argv);

    GError *error = nullptr;
    // Create the pipeline.
    GstElement *pipeline = gst_parse_launch(pipelineStr.c_str(), &error);
    if (!pipeline) {
        std::cerr << "Failed to create pipeline: " << (error ? error->message : "unknown error") << std::endl;
        if (error) g_error_free(error);
        return -1;
    }

    // Set the pipeline to PLAYING state.
    GstStateChangeReturn ret = gst_element_set_state(pipeline, GST_STATE_PLAYING);
    if (ret == GST_STATE_CHANGE_FAILURE) {
        std::cerr << "Unable to set the pipeline to the playing state." << std::endl;
        gst_object_unref(pipeline);
        return -1;
    }

    // Retrieve the appsink element from the pipeline.
    GstElement *appsinkElem = gst_bin_get_by_name(GST_BIN(pipeline), "mysink");
    if (!appsinkElem) {
        std::cerr << "Failed to get appsink element from pipeline." << std::endl;
        gst_object_unref(pipeline);
        return -1;
    }

    GstAppSink *appsink = GST_APP_SINK(appsinkElem);

    std::cout << "Streaming... Press 'q' in the video window to quit." << std::endl;

    // Main loop: Pull samples from the appsink and convert to OpenCV Mat.
    while (true) {
        // Pull a sample (blocking call).
        GstSample *sample = gst_app_sink_pull_sample(appsink);
        if (!sample) {
            std::cerr << "Failed to pull sample from appsink." << std::endl;
            break;
        }

        // Retrieve buffer and capabilities.
        GstBuffer *buffer = gst_sample_get_buffer(sample);
        GstCaps *caps = gst_sample_get_caps(sample);
        if (!caps) {
            std::cerr << "Failed to get caps from sample." << std::endl;
            gst_sample_unref(sample);
            continue;
        }

        // Get video frame dimensions from the caps structure.
        GstStructure *s = gst_caps_get_structure(caps, 0);
        int width = 0, height = 0;
        if (!gst_structure_get_int(s, "width", &width) ||
            !gst_structure_get_int(s, "height", &height)) {
            std::cerr << "Failed to retrieve width/height from caps." << std::endl;
            gst_sample_unref(sample);
            continue;
        }

        // Map the buffer to access the image data.
        GstMapInfo map;
        if (!gst_buffer_map(buffer, &map, GST_MAP_READ)) {
            std::cerr << "Failed to map buffer data." << std::endl;
            gst_sample_unref(sample);
            continue;
        }

        // Create an OpenCV Mat from the mapped data.
        // Note: Cloning is necessary because the buffer memory will be unmapped.
        cv::Mat frame(height, width, CV_8UC3, (char*)map.data);
        cv::Mat frameCopy = frame.clone();

        // Unmap the buffer and release the sample.
        gst_buffer_unmap(buffer, &map);
        gst_sample_unref(sample);

        // Display the frame using OpenCV.
        cv::imshow("UDP Video Stream", frameCopy);
        if (cv::waitKey(1) == 'q') {
            break;
        }
    }

    // Clean up: set pipeline state to NULL and unref objects.
    gst_element_set_state(pipeline, GST_STATE_NULL);
    gst_object_unref(appsinkElem);
    gst_object_unref(pipeline);
    cv::destroyAllWindows();

    return 0;
}