gstreamer with SDL

Main.cpp

#include <gst/gst.h>
#include <thread>
#include <iostream>
#include <gst/app/gstappsink.h>
#include <SDL.h>


// SDL window dimensions
#define SCREEN_WIDTH 640
#define SCREEN_HEIGHT 480

bool quit = false;

#define VERIFY_GST_NULL(ELEMENT) if (!ELEMENT) {std::cout << ">>>>>>>" << #ELEMENT " is null!" << std::endl; return 0;}

int main(int argc, char *argv[]) {
    // Initialize GStreamer
    gst_init(0, NULL);

    // Create the pipeline
    GstElement *pipeline = gst_pipeline_new("video-player");
    GstElement* videoSrc = gst_element_factory_make("videotestsrc", "video_src");
    GstElement *videoConvert = gst_element_factory_make("videoconvert", "video_decoder");
    GstAppSink *sink = GST_APP_SINK(gst_element_factory_make("appsink", "sink"));

    VERIFY_GST_NULL(pipeline)
    VERIFY_GST_NULL(videoConvert)
    VERIFY_GST_NULL(sink)


    auto videoConvert_src_pad = gst_element_get_static_pad(videoConvert, "src");
    auto videoConvert_src_caps = gst_caps_new_simple("video/x-raw",
                                                    "format", G_TYPE_STRING, "BGRA",
                                                    "width", G_TYPE_INT, SCREEN_WIDTH,
                                                    "height", G_TYPE_INT, SCREEN_HEIGHT,
                                                    NULL);
    gst_pad_set_caps(videoConvert_src_pad, videoConvert_src_caps);


    // Set the sink element to push data to the app
    gst_app_sink_set_emit_signals(sink, true);
    gst_app_sink_set_drop(sink, true);
    gst_app_sink_set_max_buffers(sink, 1);
    gst_app_sink_set_caps(sink, gst_caps_new_simple("video/x-raw",
                                                    "format", G_TYPE_STRING, "BGRA",
                                                    "width", G_TYPE_INT, SCREEN_WIDTH,
                                                    "height", G_TYPE_INT, SCREEN_HEIGHT,
                                                    NULL));

    gst_bin_add_many(GST_BIN (pipeline),
                     videoSrc,
                     videoConvert,
                     sink,
                     NULL);
    gst_element_link_many(videoSrc, videoConvert, sink, NULL);


    // Start the pipeline
    gst_element_set_state(pipeline, GST_STATE_PLAYING);

    // Create the SDL window
    SDL_Init(SDL_INIT_VIDEO);
    SDL_Window *window = SDL_CreateWindow("GStreamer + SDL",  SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN);

    // Create the SDL renderer
    auto renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED);

    // Create the SDL surface
    auto surface = SDL_CreateRGBSurface(0, SCREEN_WIDTH, SCREEN_HEIGHT, 32, 0, 0, 0, 0);

    SDL_Event e;
    while (!quit) {
        // Get the buffer from the appsink
        GstSample *sample = gst_app_sink_pull_sample(sink);
        if (!sample)
        {
            std::cout << ">>>>> No Sample from appsink!\n";
            std::this_thread::sleep_for(std::chrono::milliseconds(100));
            continue;
        }

        GstBuffer *buffer = gst_sample_get_buffer(sample);

        // Get the buffer data
        GstMapInfo info;
        gst_buffer_map(buffer, &info, GST_MAP_READ);

        SDL_LockSurface(surface);
        memcpy(surface->pixels, info.data, surface->pitch * surface->h);
        SDL_UnlockSurface(surface);

        // Unmap the buffer
        gst_buffer_unmap(buffer, &info);
        // Release the sample
        gst_sample_unref(sample);

        auto texture = SDL_CreateTextureFromSurface(renderer, surface);
        SDL_RenderCopy(renderer, texture, NULL, NULL);
        SDL_DestroyTexture(texture);
        SDL_RenderPresent(renderer);


        while (SDL_PollEvent(&e)) {
            if (e.type == SDL_QUIT) {
                quit = 1;
                break;
            }
        }

        std::this_thread::sleep_for(std::chrono::milliseconds(100));
    }


    // Stop the pipeline
    gst_element_set_state(pipeline, GST_STATE_NULL);

    // Release the GStreamer elements 
    //gst_object_unref(sink);
    //gst_object_unref(videoConvert);
    //gst_object_unref(videoSrc);
    //gst_object_unref(pipeline);


    return 0;
}