gstreamer播放mp4 c代码

以下是Linux平台C语言利用GStreamer实现mp4格式视频播放的代码，包括管道配置，连接，以及动态连接element的pad。其中难点在于demux控件通过回调方式进行音视频的分流，连接解码器、sink输出。

#include <gst/gst.h>

typedef struct _CustomData {
  GstElement *pipeline;
  GstElement *source;
  GstElement *demuxer;
  GstElement *audio_decoder;
  GstElement *video_decoder;
  GstElement *audio_sink;
  GstElement *video_sink;
  GstElement *convert;
  GstElement *resample;
  GstElement *audio_queue;
  GstElement *video_queue;
  GstElement *video_convert;
  GstElement *video_scale;
  GstElement *video_filter;
  GstElement *audio_filter;
  GstElement *audio_convert;
  GstElement *audio_resample;
  GstElement *audio_sink2;
  GstElement *video_sink2;
  GstBus *bus;
  guint bus_watch_id;
  gboolean is_live;
} CustomData;

static void pad_added_handler (GstElement *src, GstPad *new_pad, CustomData *data);

int main(int argc, char *argv[]) {
  CustomData data;
  GstStateChangeReturn ret;
  GstPad *audio_sink_pad = NULL;
  GstPad *video_sink_pad = NULL;
  GstPad *audio_src_pad = NULL;
  GstPad *video_src_pad = NULL;
  GstCaps *audio_caps = NULL;
  GstCaps *video_caps = NULL;
  GstCaps *filter_caps = NULL;
  GstCaps *convert_caps = NULL;
  GstCaps *scale_caps = NULL;
  GstCaps *resample_caps = NULL;
  GstCaps *audio_convert_caps = NULL;
  GstCaps *audio_resample_caps = NULL;
  GstCaps *audio_filter_caps = NULL;
  GstCaps *video_filter_caps = NULL;
  GstCaps *video_convert_caps = NULL;
  GstCaps *video_scale_caps = NULL;

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

  /* Initialize our data structure */
  memset (&data, 0, sizeof (data));
  data.is_live = FALSE;

  /* Create the elements */
  data.source = gst_element_factory_make ("filesrc", "source");
  data.demuxer = gst_element_factory_make ("qtdemux", "demuxer");
  data.audio_decoder = gst_element_factory_make ("decodebin", "audio_decoder");
  data.video_decoder = gst_element_factory_make ("decodebin", "video_decoder");
  data.convert = gst_element_factory_make ("videoconvert", "convert");
  data.resample = gst_element_factory_make ("audioresample", "resample");
  data.audio_queue = gst_element_factory_make ("queue", "audio_queue");
  data.video_queue = gst_element_factory_make ("queue", "video_queue");
  data.audio_sink = gst_element_factory_make ("autoaudiosink", "audio_sink");
  data.video_sink = gst_element_factory_make ("autovideosink", "video_sink");
  data.video_convert = gst_element_factory_make ("videoconvert", "video_convert");
  data.video_scale = gst_element_factory_make ("videoscale", "video_scale");
  data.video_filter = gst_element_factory_make ("capsfilter", "video_filter");
  data.audio_filter = gst_element_factory_make ("capsfilter", "audio_filter");
  data.audio_convert = gst_element_factory_make ("audioconvert", "audio_convert");
  data.audio_resample = gst_element_factory_make ("audioresample", "audio_resample");
  data.audio_sink2 = gst_element_factory_make ("alsasink", "audio_sink2");
  data.video_sink2 = gst_element_factory_make ("xvimagesink", "video_sink2");

  /* Create the empty pipeline */
  data.pipeline = gst_pipeline_new ("test-pipeline");

  if (!data.pipeline || !data.source || !data.demuxer || !data.audio_decoder || !data.video_decoder || !data.convert || !data.resample || !data.audio_queue || !data.video_queue || !data.audio_sink || !data.video_sink || !data.video_convert || !data.video_scale || !data.video_filter || !data.audio_filter || !data.audio_convert || !data.audio_resample || !data.audio_sink2 || !data.video_sink2) {
    g_printerr ("Not all elements could be created.\n");
    return -1;
  }

  /* Build the pipeline */
  gst_bin_add_many (GST_BIN (data.pipeline), data.source, data.demuxer, data.audio_decoder, data.video_decoder, data.convert, data.resample, data.audio_queue, data.video_queue, data.audio_sink, data.video_sink, data.video_convert, data.video_scale, data.video_filter, data.audio_filter, data.audio_convert, data.audio_resample, data.audio_sink2, data.video_sink2, NULL);
  if (gst_element_link (data.source, data.demuxer) != TRUE ||
      gst_element_link_many (data.audio_queue, data.audio_convert, data.audio_resample, data.audio_filter, data.audio_sink2, NULL) != TRUE ||
      gst_element_link_many (data.video_queue, data.video_convert, data.video_scale, data.video_filter, data.video_sink2, NULL) != TRUE) {
    g_printerr ("Elements could not be linked.\n");
    gst_object_unref (data.pipeline);
    return -1;
  }

  /* Set the URI to play */
  g_object_set (data.source, "location", argv[1], NULL);

  /* Connect to the pad-added signal */
  g_signal_connect (data.demuxer, "pad-added", G_CALLBACK (pad_added_handler), &data);

  /* Start playing */
  ret = gst_element_set_state (data.pipeline, GST_STATE_PLAYING);
  if (ret == GST_STATE_CHANGE_FAILURE) {
    g_printerr ("Unable to set the pipeline to the playing state.\n");
    gst_object_unref (data.pipeline);
    return -1;
  }

  /* Wait until error or EOS */
  data.bus = gst_element_get_bus (data.pipeline);
  data.bus_watch_id = gst_bus_add_watch (data.bus, bus_call, loop);
  gst_object_unref (data.bus);
  g_main_loop_run (loop);

  /* Free resources */
  gst_element_set_state (data.pipeline, GST_STATE_NULL);
  gst_object_unref (data.pipeline);
  return 0;
}

static void pad_added_handler (GstElement *src, GstPad *new_pad, CustomData *data) {
  GstPad *sink_pad = NULL;
  GstPadLinkReturn ret;
  GstCaps *new_pad_caps = NULL;
  GstStructure *new_pad_struct = NULL;
  const gchar *new_pad_type = NULL;

  g_print ("Received new pad '%s' from '%s':\n", GST_PAD_NAME (new_pad), GST_ELEMENT_NAME (src));

  /* Check the new pad's type */
  new_pad_caps = gst_pad_get_current_caps (new_pad);
  new_pad_struct = gst_caps_get_structure (new_pad_caps, 0);
  new_pad_type = gst_structure_get_name (new_pad_struct);
  if (g_str_has_prefix (new_pad_type, "audio/x-raw")) {
    sink_pad = gst_element_get_static_pad (data->audio_queue, "sink");
    g_print ("Linking audio demuxer to audio queue.\n");
  } else if (g_str_has_prefix (new_pad_type, "video/x-raw")) {
    sink_pad = gst_element_get_static_pad (data->video_queue, "sink");
    g_print ("Linking video demuxer to video queue.\n");
  } else {
    g_print ("It has type '%s' which is not raw audio. Ignoring.\n", new_pad_type);
    goto exit;
  }

  /* If we have an unlinked sink pad, link it now */
  if (gst_pad_is_linked (sink_pad)) {
    g_print ("We are already linked. Ignoring.\n");
    goto exit;
  }

  /* Attempt the link */
  ret = gst_pad_link (new_pad, sink_pad);
  if (GST_PAD_LINK_FAILED (ret)) {
    g_print ("Type is '%s' but link failed.\n", new_pad_type);
  } else {
    g_print ("Link succeeded (type '%s').\n", new_pad_type);
  }

exit:
  /* Unreference the new pad's caps, if we got them */
  if (new_pad_caps != NULL)
    gst_caps_unref (new_pad_caps);

  /* Unreference the sink pad */
  if (sink_pad != NULL)
    gst_object_unref (sink_pad);
}