c - 用gstreamer编写ogg播放器

Question

我是 gstreamer 新手，我想从头开始编写一个 ogg 播放器。
到目前为止，我可以编写音频部分，该部分从 ogg 视频文件中播放音频。我的具体问题是如何处理来自解复用器的视频和音频。简而言之，我想在管道下面实现。但我不知道如何分割解复用器的音频和视频接收器并将它们连接到适当的解码器。 处理音频部分的代码在这里(存在于互联网上):

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


static gboolean
bus_call (GstBus     *bus,
          GstMessage *msg,
          gpointer    data)
{
  GMainLoop *loop = (GMainLoop *) data;

  switch (GST_MESSAGE_TYPE (msg)) {

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

      g_main_loop_quit (loop);
      break;
    }
    default:
      break;
  }

  return TRUE;
}


static void
on_pad_added (GstElement *element,
              GstPad     *pad,
              gpointer    data)
{
  GstPad *sinkpad;
  GstElement *decoder = (GstElement *) data;

  /* We can now link this pad with the vorbis-decoder sink pad */
  g_print ("Dynamic pad created, linking demuxer/decoder\n");

  sinkpad = gst_element_get_static_pad (decoder, "sink");

  gst_pad_link (pad, sinkpad);

  gst_object_unref (sinkpad);
}



int
main (int   argc,
      char *argv[])
{
  GMainLoop *loop;

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

  /* Initialisation */
  gst_init (&argc, &argv);

  loop = g_main_loop_new (NULL, FALSE);


  /* Check input arguments */
  if (argc != 2) {
    g_printerr ("Usage: %s <Ogg/Vorbis filename>\n", argv[0]);
    return -1;
  }


  /* Create gstreamer elements */
  pipeline = gst_pipeline_new ("audio-player");
  source   = gst_element_factory_make ("filesrc",       "file-source");
  demuxer  = gst_element_factory_make ("oggdemux",      "ogg-demuxer");
  decoder  = gst_element_factory_make ("vorbisdec",     "vorbis-decoder");
  conv     = gst_element_factory_make ("audioconvert",  "converter");
  sink     = gst_element_factory_make ("autoaudiosink", "audio-output");

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

  /* Set up the pipeline */

  /* we set the input filename to the source element */
  g_object_set (G_OBJECT (source), "location", argv[1], NULL);

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

  /* we add all elements into the pipeline */
  /* file-source | ogg-demuxer | vorbis-decoder | converter | alsa-output */
  gst_bin_add_many (GST_BIN (pipeline),
                    source, demuxer, decoder, conv, sink, NULL);

  /* we link the elements together */
  /* file-source -> ogg-demuxer ~> vorbis-decoder -> converter -> alsa-output */
  gst_element_link (source, demuxer);
  gst_element_link_many (decoder, conv, sink, NULL);
  g_signal_connect (demuxer, "pad-added", G_CALLBACK (on_pad_added), decoder);

  /* Set the pipeline to "playing" state*/
  g_print ("Now playing: %s\n", argv[1]);
  gst_element_set_state (pipeline, GST_STATE_PLAYING);


  /* Iterate */
  g_print ("Running...\n");
  g_main_loop_run (loop);


  /* Out of the main loop, clean up nicely */
  g_print ("Returned, stopping playback\n");
  gst_element_set_state (pipeline, GST_STATE_NULL);

  g_print ("Deleting pipeline\n");
  gst_object_unref (GST_OBJECT (pipeline));
  g_source_remove (bus_watch_id);
  g_main_loop_unref (loop);

  return 0;
}

Answer 1

这是一个通过 gst-launch 运行 Vorbis 和 Theora 解码器的管道:

gst-launch-1.0 filesrc location=video.ogg ! oggdemux name=demuxer ! vorbisdec ! audioconvert ! audioresample ! autoaudiosink demuxer. ! queue ! theoradec ! autovideosink

要在 C 中执行此操作，只需创建更多视频元素，然后通过将它们添加到 gst_bin_add_many() 来将它们全部添加到 pipeline bin 中。然后根据您想要的拓扑，使用 gst_element_link() 或 gst_element_link_many() 将它们相互链接。