无法使用 c 中的简单示例使用 GStreamer 启动视频

Question

我正在尝试使用 C 代码启动 .mp4 视频，我找到了这个简单的示例，但是元素 videoenc 始终为 null，并且我总是收到无法创建 videoenc 的错误。这是完整的代码：

#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;
}

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

  GstElement *pipeline, *videosrc, *colorspace, *videoenc,
    *videoq, *audiosrc, *conv, *audioenc, *audioq, *muxer, *sink;

  GstBus *bus;

  /* Initialisation */
  gst_init (NULL, NULL);

  loop = g_main_loop_new (NULL, FALSE);

  /* Create gstreamer elements */
  pipeline = gst_pipeline_new ("audio-player");
  videosrc = gst_element_factory_make ("filesrc", "videosrc");
  muxer = gst_element_factory_make ("qtdemux", "mux");
  videoenc = gst_element_factory_make ("ffdec_mpeg4", "videoenc");
  sink = gst_element_factory_make ("autovideosink", "sink");

  if(!videoenc)
  {
      printf("could not create videoenc \n");
  }
  if (!pipeline || !videosrc || !muxer || !videoenc
       || !sink) {
    g_printerr ("One element could not be created. Exiting.\n");
    return -1;
  }

  /* Set up the pipeline */
  g_print ("Elements are created\n");

  /* set the properties of other elements */
  g_object_set (G_OBJECT (videosrc), "location", "/home/user/somevideo.mp4", NULL);

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

  /* we add all elements into the pipeline */
  gst_bin_add_many (GST_BIN (pipeline),
    videosrc, muxer, videoenc,
    sink, NULL);

  g_print ("Added all the Elements into the pipeline\n");

  /* we link the elements together */
  gst_element_link_many (videosrc, muxer, videoenc, sink,
      NULL);

  g_print ("Linked all the Elements together\n");
  /* Set the pipeline to "playing" state*/
  g_print ("Playing the video\n");
  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));

  return 0;
}

我也试过使用这个命令

gst-launch-1.0 -v filesrc location=/home/user/somevideo.mp4 ! qtdemux ! ffdec_mpeg4 ! autovideosink

我在终端错误中看到的错误：ffdec_mpeg4 未找到

请帮助我在 Ubuntu 16.04 中使用 c 代码启动视频。

Answer 1

您确定 MP4 文件包含 MPEG4 视频吗？也许是 H.264？无论如何，名称方案似乎来自旧版本的 GStreamer。较新的名称是 avdec_mpeg4。但请确保您安装了 libav Gstreamer 插件。

无法使用 c 中的简单示例使用 GStreamer 启动视频

Can not launch video with GStreamer using simple example in c

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