Qt와 GStreamer 로 작성한 flac 오디오 재생 예제

라즈베리파이 4 미디어 플레이어를 개발하기 위해 Qt와 GStreamer 로 아주 단간하게 테스트용도로 작성한 flac 오디오 재생 프로그램. (Qt Multimedia 가 아님) GStreamer의 Hello world 소스코드 일부를 수정하였고 flac 오디오 파일을 재생 시킨다.. 

#include <gst/gst.h>

class MediaPlayer::MediaPlayerImpl
{
public:
    MediaPlayerImpl()
        : pipeline(nullptr), source(nullptr), demuxer(nullptr), decoder(nullptr), conv(nullptr), sink(nullptr)
        , bus(nullptr), bus_watch_id(0)
    {

    }

    static gboolean bus_call (GstBus *bus, GstMessage *msg, gpointer data)
    {
      switch (GST_MESSAGE_TYPE (msg)) {

        case GST_MESSAGE_EOS:
          g_print ("End of stream\n");

          break;

        case GST_MESSAGE_ERROR: {
          gchar  *debug;
          GError *error;

          gst_message_parse_error (msg, &error, &debug);
          g_free (debug);

          g_printerr ("Error: %s\n", error->message);
          g_error_free (error);

          break;
        }
        default:
          break;
      }

      return TRUE;
    }

    GstElement *pipeline, *source, *demuxer, *decoder, *conv, *sink;
    GstBus *bus;
    guint bus_watch_id;
};


MediaPlayer::MediaPlayer()
    :pImpl(std::make_shared<MediaPlayerImpl>())
{

}

MediaPlayer::~MediaPlayer()
{
    /* Out of the main loop, clean up nicely */
     g_print ("Returned, stopping playback\n");
     gst_element_set_state (pImpl->pipeline, GST_STATE_NULL);

     g_print ("Deleting pipeline\n");
     gst_object_unref (GST_OBJECT (pImpl->pipeline));
     g_source_remove (pImpl->bus_watch_id);
}

int MediaPlayer::init(int *argc, char **argv[])
{
    /* Initialisation */
    gst_init (argc, argv);

    /* Create gstreamer elements */
    pImpl->pipeline = gst_pipeline_new ("audio-player");
    pImpl->source   = gst_element_factory_make ("filesrc",       "file-source");
    pImpl->demuxer  = gst_element_factory_make ("flacparse",      "flacparse-demuxer");
    pImpl->decoder  = gst_element_factory_make ("flacdec",     "flacdec-decoder");
    pImpl->sink     = gst_element_factory_make ("autoaudiosink", "audio-output");

    if (!pImpl->pipeline || !pImpl->source || !pImpl->demuxer || !pImpl->decoder || !pImpl->sink) {
        g_printerr ("One element could not be created. Exiting.\n");
        return -1;
    }

    /* we add a message handler */
    pImpl->bus = gst_pipeline_get_bus (GST_PIPELINE (pImpl->pipeline));
    pImpl->bus_watch_id = gst_bus_add_watch (pImpl->bus, pImpl->bus_call, nullptr);
    gst_object_unref (pImpl->bus);

    /* we add all elements into the pipeline */
    /* file-source | flacparse | flacdec-decoder | alsa-output */
    gst_bin_add_many (GST_BIN (pImpl->pipeline),
                      pImpl->source, pImpl->demuxer, pImpl->decoder, pImpl->sink, NULL);

    /* we link the elements together */
    /* file-source -> flacparse ~> flacdec-decoder -> alsa-output */

    gst_element_link_many (pImpl->source, pImpl->demuxer, pImpl->decoder, pImpl->sink, NULL);

    return 0;
}

void MediaPlayer::setSourcePath(const QString &path)
{
    /* we set the input filename to the source element */
    g_object_set (G_OBJECT (pImpl->source), "location", path.toStdString().c_str(), NULL);
}

void MediaPlayer::play()
{
    /* Set the pipeline to "playing" state*/
    gst_element_set_state (pImpl->pipeline, GST_STATE_PLAYING);
}

void MediaPlayer::pause()
{
    /* Set the pipeline to "pause" state*/
    gst_element_set_state (pImpl->pipeline, GST_STATE_PAUSED);
}

void MediaPlayer::stop()
{
    /* Set the pipeline to "stop" state*/
    gst_element_set_state (pImpl->pipeline, GST_STATE_NULL);
}

예제의 GStreamer 파이프라인

FLAC Audio Playback

mediaplayer.tar.gz

https://gstreamer.freedesktop.org/documentation/application-development/basics/helloworld.html