GStreamer Basic tutorial 13 Playback Speed

   #include <string.h>
   #include <stdio.h>
   #include <gst/gst.h>
   
   typedef struct _CustomData
   {
     GstElement *pipeline;
     GstElement *video_sink;
     GMainLoop *loop;
   
     gboolean playing;             /* Playing or Paused */
     gdouble rate;                 /* Current playback rate (can be negative) */
   } CustomData;
   
   /* Send seek event to change rate */
   static void
   send_seek_event (CustomData * data)
   {
     gint64 position;
     GstEvent *seek_event;
   
     /* Obtain the current position, needed for the seek event */
     if (!gst_element_query_position (data->pipeline, GST_FORMAT_TIME, &position)) {
       g_printerr ("Unable to retrieve current position.\n");
       return;
     }
   
     /* Create the seek event */
     if (data->rate > 0) {
       seek_event =
           gst_event_new_seek (data->rate, GST_FORMAT_TIME,
           GST_SEEK_FLAG_FLUSH | GST_SEEK_FLAG_ACCURATE, GST_SEEK_TYPE_SET,
           position, GST_SEEK_TYPE_END, 0);
     } else {
       seek_event =
           gst_event_new_seek (data->rate, GST_FORMAT_TIME,
           GST_SEEK_FLAG_FLUSH | GST_SEEK_FLAG_ACCURATE, GST_SEEK_TYPE_SET, 0,
           GST_SEEK_TYPE_SET, position);
     }
   
     if (data->video_sink == NULL) {
       /* If we have not done so, obtain the sink through which we will send the seek events */
       g_object_get (data->pipeline, "video-sink", &data->video_sink, NULL);
     }
   
     /* Send the event */
     gst_element_send_event (data->video_sink, seek_event);
   
     g_print ("Current rate: %g\n", data->rate);
   }
   
   /* Process keyboard input */
   static gboolean
   handle_keyboard (GIOChannel * source, GIOCondition cond, CustomData * data)
   {
     gchar *str = NULL;
   
     if (g_io_channel_read_line (source, &str, NULL, NULL,
             NULL) != G_IO_STATUS_NORMAL) {
       return TRUE;
     }
   
     switch (g_ascii_tolower (str[0])) {
       case 'p':
         data->playing = !data->playing;
         gst_element_set_state (data->pipeline,
             data->playing ? GST_STATE_PLAYING : GST_STATE_PAUSED);
         g_print ("Setting state to %s\n", data->playing ? "PLAYING" : "PAUSE");
         break;
       case 's':
         if (g_ascii_isupper (str[0])) {
           data->rate *= 2.0;
         } else {
           data->rate /= 2.0;
         }
         send_seek_event (data);
         break;
       case 'd':
         data->rate *= -1.0;
         send_seek_event (data);
         break;
       case 'n':
         if (data->video_sink == NULL) {
           /* If we have not done so, obtain the sink through which we will send the step events */
           g_object_get (data->pipeline, "video-sink", &data->video_sink, NULL);
         }
   
         gst_element_send_event (data->video_sink,
             gst_event_new_step (GST_FORMAT_BUFFERS, 1, ABS (data->rate), TRUE,
                 FALSE));
         g_print ("Stepping one frame\n");
         break;
       case 'q':
         g_main_loop_quit (data->loop);
         break;
       default:
         break;
     }
   
     g_free (str);
   
     return TRUE;
   }
   
   int
   main (int argc, char *argv[])
   {
     CustomData data;
     GstStateChangeReturn ret;
     GIOChannel *io_stdin;
   
     /* Initialize GStreamer */
     gst_init (&argc, &argv);
   
     /* Initialize our data structure */
     memset (&data, 0, sizeof (data));
   
     /* Print usage map */
     g_print ("USAGE: Choose one of the following options, then press enter:\n"
         " 'P' to toggle between PAUSE and PLAY\n"
         " 'S' to increase playback speed, 's' to decrease playback speed\n"
         " 'D' to toggle playback direction\n"
         " 'N' to move to next frame (in the current direction, better in PAUSE)\n"
         " 'Q' to quit\n");
   
     /* Build the pipeline */
     data.pipeline =
         gst_parse_launch
         ("playbin uri=https://www.freedesktop.org/software/gstreamer-sdk/data/media/sintel_trailer-480p.webm",
         NULL);
   
     /* Add a keyboard watch so we get notified of keystrokes */
   #ifdef G_OS_WIN32
     io_stdin = g_io_channel_win32_new_fd (fileno (stdin));
   #else
     io_stdin = g_io_channel_unix_new (fileno (stdin));
   #endif
     g_io_add_watch (io_stdin, G_IO_IN, (GIOFunc) handle_keyboard, &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;
     }
     data.playing = TRUE;
     data.rate = 1.0;
   
     /* Create a GLib Main Loop and set it to run */
     data.loop = g_main_loop_new (NULL, FALSE);
     g_main_loop_run (data.loop);
   
     /* Free resources */
     g_main_loop_unref (data.loop);
     g_io_channel_unref (io_stdin);
     gst_element_set_state (data.pipeline, GST_STATE_NULL);
     if (data.video_sink != NULL)
       gst_object_unref (data.video_sink);
     gst_object_unref (data.pipeline);
     return 0;
   }