main.c

/* We are trying to replicate
    gst-launch-1.0 -e v4l2src device=/dev/video0 ! videoconvert ! queue ! tee name=t t. ! matroskamux ! queue ! filesink location=/tmp/test.mkv t. ! queue ! autovideosink sync=false

Use "gcc -o test main.c `pkg-config --libs --cflags gtk+-3.0 gstreamer-1.0`" to compile.

Sorry but I was too lazy to add error checking for every single possible failure, but I did add error checking for the most
frequent failures. I hope you don't mind. */

#include <gtk/gtk.h>
#include <gst/gst.h>

// Some basic options.
#define CAMERA_PATH "/dev/video0"   // Path to the camera input file.
#define FILE_NAME "/tmp/test.mkv"   // Path of the output.
#define PREVIEW_SYNC FALSE      // Synchronize the screen output?

// State of the pipeline.
static gboolean recording = TRUE;

// Return codes, first one designates success, all others various failure errors.
enum ReturnCodes {
            RETURN_SUCCESS,             // Everything is OK (no error).
            RETURN_CANNOT_CREATE_PIPELINE_ELEMENTS, // At least one pipeline element could not be created.
            RETURN_CANNOT_LINK_PIPELINE_ELEMENTS,   // At least one pipeline element could not be linked.
        };

// Widgets constituting our window.
struct Window
{
    GtkWidget *window;      // Window itself.
    GtkWidget *box;         // Box attached to the window, holds other elements.
    GtkWidget *button_pause;    // Button that pauses recording of the video.
    GtkWidget *button_stop;     // Button that stops recording of the video, closing the application.
};

// Our pipeline for recording and displaying video.
struct Pipeline
{
    GstElement *pipeline;       // Pipeline itself, contains other elements.
    GstElement *source;     // Video source (camera).
    GstElement *converter;      // To convert source data to raw video stream.
    GstElement *queue_source;   // Queue collecting converted video source data.
    GstElement *tee;        // Tee connecting video source to the preview window and file.
    GstPad *tee_src_preview;    // Tee source pad connected to the preview.
    GstPad *tee_src_file;       // Tee source pad connected to the file.
    GstElement *queue_preview;  // Collects data from preview pad of the tee and forwards it toward the preview window.
    GstElement *preview;        // Preview window.
    GstElement *queue_format;   // Collects data from file pad of the tee and forwards it toward formatting sink.
    GstElement *format;     // Encodes the data into a video format (here MKV).
    GstPad *format_sink_video;  // Video sink pad of the formatter.
    GstElement *queue_file;     // Forwards the encoded data toward a file / sink if output is unpaused / paused, respectively.
    GstElement *sink_file;      // File to which we write video source.
    GstElement *sink_fake;      // Fake sink that discards anything that's written to it, we will use it for implementing pause functionality.
};

static void print_error(const int error_code)
{
    g_printerr("Error: ");

    // Print error according to the supplied error code.
    switch (error_code)
    {
        case RETURN_CANNOT_CREATE_PIPELINE_ELEMENTS:
            g_printerr("Not all pipeline elements could be created.");
            break;
        case RETURN_CANNOT_LINK_PIPELINE_ELEMENTS:
            g_printerr("Not all pipeline elements could be linked.");
            break;
        default:
            g_printerr("Unknown error code.");
    }

    g_printerr("\n");
}

static void action_pause(GtkWidget *button, struct Pipeline * const pipeline)
{
    // Get the current recording state.
    recording = !recording;

    // Change button's text accordingly and replace file sink with fake sink
    // to pause the recording or fake sink with file sink to resume it.
    if (recording)  // We're recording, unpause.
    {
        // Replace fake sink with file sink.
        if (gst_element_set_state(pipeline->pipeline, GST_STATE_PAUSED))
        gst_element_set_state(pipeline->sink_fake, GST_STATE_NULL);
        gst_element_unlink(pipeline->queue_file, pipeline->sink_fake);
        gst_bin_remove(GST_BIN(pipeline->pipeline), pipeline->sink_fake);
        gst_bin_add(GST_BIN(pipeline->pipeline), pipeline->sink_file);
        gst_element_link(pipeline->queue_file, pipeline->sink_file);
        gst_element_set_state(pipeline->pipeline, GST_STATE_PLAYING);

        // Change button's text so it says "Pause".
        gtk_button_set_label(GTK_BUTTON(button), "Pause");
    }
    else    // We're not recording, pause.
    {
        // Replace file sink with fake sink.
        gst_element_set_state(pipeline->pipeline, GST_STATE_PAUSED);
        gst_element_set_state(pipeline->sink_file, GST_STATE_NULL);
        gst_element_unlink(pipeline->queue_file, pipeline->sink_file);
        gst_bin_remove(GST_BIN(pipeline->pipeline), pipeline->sink_file);
        gst_bin_add(GST_BIN(pipeline->pipeline), pipeline->sink_fake);
        gst_element_link(pipeline->queue_file, pipeline->sink_fake);
        gst_element_set_state(pipeline->pipeline, GST_STATE_PLAYING);

        // Change button's text so it says "Unpause".
        gtk_button_set_label(GTK_BUTTON(button), "Unpause");
    }
}

static void action_stop(GtkWidget *button, struct Pipeline * const pipeline)
{
    gst_element_send_event(pipeline->pipeline, gst_event_new_eos());

    GstBus *bus = gst_pipeline_get_bus(GST_PIPELINE(pipeline->pipeline));
    GstMessage *msg = gst_bus_timed_pop_filtered(bus, GST_CLOCK_TIME_NONE, GST_MESSAGE_EOS);
    gst_object_unref(bus);

    gst_message_unref(msg);

    // Destroy all internal components of the pipeline.
    gst_element_set_state(pipeline->pipeline, GST_STATE_NULL);

    /* The following is not really necessary.
    // Unlink all elements.
    if (recording)
    {
        gst_element_unlink(pipeline->queue_file, pipeline->sink_file);
        gst_bin_remove(GST_BIN(pipeline->pipeline), pipeline->sink_file);
    }
    else
    {
        gst_element_unlink(pipeline->queue_file, pipeline->sink_fake);
        gst_bin_remove(GST_BIN(pipeline->pipeline), pipeline->sink_fake);
    }
    gst_element_unlink(pipeline->format, pipeline->queue_file);
    gst_pad_unlink(gst_element_get_static_pad(pipeline->queue_format, "src"), pipeline->format_sink_video);
    gst_pad_unlink(pipeline->tee_src_file, gst_element_get_static_pad(pipeline->queue_format, "sink"));
    gst_element_unlink(pipeline->queue_preview, pipeline->preview);
    gst_pad_unlink(pipeline->tee_src_preview, gst_element_get_static_pad(pipeline->queue_preview, "sink"));
    gst_element_unlink_many(pipeline->source, pipeline->queue_source, pipeline->tee, NULL);

    // Remove all remaining elements.
    gst_bin_remove_many(GST_BIN(pipeline->pipeline), pipeline->source, pipeline->queue_source, pipeline->tee, pipeline->queue_preview, pipeline->preview, pipeline->queue_format, pipeline->format, pipeline->queue_file, NULL);
    */

    // Destroy all requested pads.
    gst_object_unref(pipeline->tee_src_preview);
    gst_object_unref(pipeline->tee_src_file);
    gst_object_unref(pipeline->format_sink_video);

    // Destroy the pipeline.
    gst_object_unref(pipeline->pipeline);

    // Terminate the application.
    gtk_main_quit();
}

static void create_window(struct Window * const window)
{
    // Create window and set its properties.
    window->window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    gtk_window_set_default_size(GTK_WINDOW(window->window), 100, 100);
    gtk_window_set_title(GTK_WINDOW(window->window), "Test GStreamer");
    gtk_window_set_resizable(GTK_WINDOW(window->window), FALSE);

    // Create main box and populate it with buttons.
    window->box = gtk_box_new(GTK_ORIENTATION_VERTICAL, 0);
    window->button_pause = gtk_button_new_with_label("Pause");
    window->button_stop = gtk_button_new_with_label("Stop");
    gtk_box_pack_start(GTK_BOX(window->box), window->button_pause, TRUE, TRUE, 0);
    gtk_box_pack_start(GTK_BOX(window->box), window->button_stop, TRUE, TRUE, 0);

    // Attach everything to the window.
    gtk_container_add(GTK_CONTAINER(window->window), window->box);
}

static void connect_signals(struct Window * const window, struct Pipeline * const pipeline)
{
    // Connect widgets signals to event handlers.
    g_signal_connect(window->window, "delete-event", G_CALLBACK(action_stop), pipeline);
    g_signal_connect(window->button_pause, "clicked", G_CALLBACK(action_pause), pipeline);
    g_signal_connect(window->button_stop, "clicked", G_CALLBACK(action_stop), pipeline);
}

static int create_pipeline(struct Pipeline * const pipeline)
{
    // Create pipeline to hold all GStreamer elements.
    pipeline->pipeline = gst_pipeline_new(NULL);

    // Create all needed gstreamer elements.
    pipeline->source = gst_element_factory_make("v4l2src", NULL);
    pipeline->converter = gst_element_factory_make("videoconvert", NULL);
    pipeline->queue_source = gst_element_factory_make("queue", NULL);
    pipeline->tee = gst_element_factory_make("tee", NULL);
    pipeline->tee_src_preview = gst_element_get_request_pad(pipeline->tee, "src_%u");
    pipeline->tee_src_file = gst_element_get_request_pad(pipeline->tee, "src_%u");
    pipeline->queue_preview = gst_element_factory_make("queue", NULL);
    pipeline->preview = gst_element_factory_make("autovideosink", NULL);
    pipeline->queue_format = gst_element_factory_make("queue", NULL);
    pipeline->format = gst_element_factory_make("matroskamux", NULL);
    pipeline->format_sink_video = gst_element_get_request_pad(pipeline->format, "video_%u");
    pipeline->queue_file = gst_element_factory_make("queue", NULL);
    pipeline->sink_file = gst_element_factory_make("filesink", NULL);
    pipeline->sink_fake = gst_element_factory_make("fakesink", NULL);

    // Check if all elements could be created.
    if (!pipeline->source || !pipeline->converter || !pipeline->queue_source || !pipeline->tee || !pipeline->tee_src_preview || !pipeline->tee_src_file || !pipeline->queue_preview || !pipeline->preview || !pipeline->queue_format || !pipeline->format || !pipeline->format_sink_video || !pipeline->queue_file || !pipeline->sink_file || !pipeline->sink_fake)
    {
        print_error(RETURN_CANNOT_CREATE_PIPELINE_ELEMENTS);
        return RETURN_CANNOT_CREATE_PIPELINE_ELEMENTS;
    }

    // Set some element properties.
    g_object_set(pipeline->source, "device", CAMERA_PATH, NULL);
    g_object_set(pipeline->sink_file, "location", FILE_NAME, "async", 0, NULL);
    g_object_set(pipeline->preview, "sync", PREVIEW_SYNC, NULL);

    // Add all elements to the pipeline (except for fake sink, since the default state is recording).
    gst_bin_add_many(GST_BIN(pipeline->pipeline), pipeline->source, pipeline->converter, pipeline->queue_source, pipeline->tee, pipeline->queue_preview, pipeline->preview, pipeline->queue_format, pipeline->format, pipeline->queue_file, pipeline->sink_file, NULL);

    // Link all elements together appropriately.
    if (!gst_element_link_many(pipeline->source, pipeline->converter, pipeline->queue_source, pipeline->tee, NULL))
    {
        print_error(RETURN_CANNOT_LINK_PIPELINE_ELEMENTS);
        return RETURN_CANNOT_LINK_PIPELINE_ELEMENTS;
    }
    if (gst_pad_link(pipeline->tee_src_preview, gst_element_get_static_pad(pipeline->queue_preview, "sink")) != GST_PAD_LINK_OK)
    {
        print_error(RETURN_CANNOT_LINK_PIPELINE_ELEMENTS);
        return RETURN_CANNOT_LINK_PIPELINE_ELEMENTS;
    }
    if (!gst_element_link(pipeline->queue_preview, pipeline->preview))
    {
        print_error(RETURN_CANNOT_LINK_PIPELINE_ELEMENTS);
        return RETURN_CANNOT_LINK_PIPELINE_ELEMENTS;
    }
    if (gst_pad_link(pipeline->tee_src_file, gst_element_get_static_pad(pipeline->queue_format, "sink")) != GST_PAD_LINK_OK)
    {
        print_error(RETURN_CANNOT_LINK_PIPELINE_ELEMENTS);
        return RETURN_CANNOT_LINK_PIPELINE_ELEMENTS;
    }
    if (gst_pad_link(gst_element_get_static_pad(pipeline->queue_format, "src"), pipeline->format_sink_video) != GST_PAD_LINK_OK)
    {
        print_error(RETURN_CANNOT_LINK_PIPELINE_ELEMENTS);
        return RETURN_CANNOT_LINK_PIPELINE_ELEMENTS;
    }
    if (!gst_element_link_many(pipeline->format, pipeline->queue_file, pipeline->sink_file, NULL))
    {
        print_error(RETURN_CANNOT_LINK_PIPELINE_ELEMENTS);
        return RETURN_CANNOT_LINK_PIPELINE_ELEMENTS;
    }

    return RETURN_SUCCESS;
}

int main()
{
    // Initialize our librarires.
    gst_init(NULL, NULL);
    gtk_init(NULL, NULL);

    // Create window and pipeline data structures.
    struct Window window;
    struct Pipeline pipeline;

    // Create window and populate it.
    create_window(&window);

    // Create pipeline.
    switch (create_pipeline(&pipeline))
    {
        case RETURN_CANNOT_CREATE_PIPELINE_ELEMENTS:
            return RETURN_CANNOT_CREATE_PIPELINE_ELEMENTS;
        case RETURN_CANNOT_LINK_PIPELINE_ELEMENTS:
            return RETURN_CANNOT_LINK_PIPELINE_ELEMENTS;
    }

    // To connect button events to function handlers.
    connect_signals(&window, &pipeline);

    // Start the program!
    gst_element_set_state(pipeline.pipeline, GST_STATE_PLAYING);
    gtk_widget_show_all(window.window);
    gtk_main();

    return RETURN_SUCCESS;
}