How to program videomixer using Gstreamer C API

[Nicolai Hess]

2012/1/6 Dejan Tolj <dejan1 at gmail.com>

> I am trying to simulate the following gstreamer pipeline using the C API:
>
> gst-launch -e videomixer name=mix ! ffmpegcolorspace ! xvimagesink \
>   videotestsrc pattern=1  ! video/x-raw-yuv,width=100,height=100 !
> videobox border-alpha=0 top=0 left=0 ! mix. \
>   videotestsrc pattern=0  ! video/x-raw-yuv,width=100,height=100 !
> videobox border-alpha=0 top=0 left=-100 ! mix.
>
> So far I have:
>
> #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;
>  GstElement *source1,*source2;
>  GstElement *scale,*filter;
>  GstElement *videobox1,*videobox2; //just one.
>  GstElement *mixer,*clrspace,*sink;
>  GstCaps *filtercaps;
>  GstBus *bus;
>
>  /* 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;
>  }*/
>
>  //gst-launch videotestsrc pattern=snow ! ximagesink
>
>  /* Create gstreamer elements */
>  pipeline = gst_pipeline_new ("player");
>  source1   = gst_element_factory_make ("videotestsrc",       "source1");
>  source2   = gst_element_factory_make ("videotestsrc",       "source2");
> //  source2   = gst_element_factory_make ("uridecodebin",
> "file-source2");
>  scale   = gst_element_factory_make ("videoscale",       "scale");
>  filter = gst_element_factory_make("capsfilter","filter");
>  videobox1 = gst_element_factory_make ("videobox",       "videobox1");
>  videobox2 = gst_element_factory_make ("videobox",       "videobox2");
>  mixer = gst_element_factory_make ("videomixer",       "mixer");
>  clrspace  = gst_element_factory_make ("ffmpegcolorspace",
> "clrspace");
>
> //  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 ("xvimagesink", "sink");
>
>  /*if (!pipeline || !source || !demuxer || !decoder || !conv || !sink) {
>    g_printerr ("One element could not be created. Exiting.\n");
>    return -1;
>  }*/
>  if (!pipeline || !source1 || !source2 || !sink) {
>    g_printerr ("One element could not be created. Exiting.\n");
>    return -1;
>  }
>
>  filtercaps = gst_caps_new_simple ("video/x-raw-yuv",
>          "width", G_TYPE_INT, 200,
>          "height", G_TYPE_INT, 100,
>          NULL);
>  g_object_set (G_OBJECT (filter), "caps", filtercaps, NULL);
>  //gst_caps_unref (filtercaps);
>
>  g_object_set(videobox1,"border-alpha",0,"top",0,"left",0,NULL);
>  g_object_set(videobox2,"border-alpha",0,"top",0,"left",-200,NULL);
>
>
>  /* Set up the pipeline */
>
>  /* we set the input filename to the source element */
>    g_object_set (G_OBJECT (source1), "pattern", 0, NULL);
>    g_object_set (G_OBJECT (source2), "pattern", 1, 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),
>                    source1,filter,videobox1,mixer,clrspace, sink,
> source2,videobox2, NULL);
>
>  /* we link the elements together */
>    //gst_element_link_many (source1, scale, filter, videobox1, mixer,
> clrspace, sink);
>    //gst_element_link_many (source2, scale, filter, videobox2, mixer,
> clrspace, sink);
>    gst_element_link_many (source1, filter, videobox1, mixer, clrspace,
> sink);
>    gst_element_link_many (source2, filter, videobox2, mixer, clrspace,
> sink);
>
>
>  /* Set the pipeline to "playing" state*/
>  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;
> }
>
>
> I have also set debugging on: export GST_DEBUG=3
>
> When I run my program I get the following error:
>
> Running...
> 0:00:00.178663884  4797  0x8937020 WARN                 basesrc
> gstbasesrc.c:2582:gst_base_src_loop:<source2> error: Internal data
> flow error.
> 0:00:00.178766444  4797  0x8937020 WARN                 basesrc
> gstbasesrc.c:2582:gst_base_src_loop:<source2> error: streaming task
> paused, reason not-linked (-1)
> Error: Internal data flow error.
> Returned, stopping playback
> 0:00:00.202571746  4797  0x893ae00 WARN           basetransform
> gstbasetransform.c:1627:gst_base_transform_prepare_output_buffer:<clrspace>
> pad-alloc failed: wrong-state
> 0:00:00.202645907  4797  0x893ae00 WARN           basetransform
> gstbasetransform.c:2335:gst_base_transform_handle_buffer:<clrspace>
> could not get buffer from pool: wrong-state
> Deleting pipeline
>
>
> Why is it complaining about source2 not-linked?
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>

// linking source2 with filter doesn't work, because filter is already
linked with source1
  gst_element_link_many (source2, filter, videobox2, mixer, clrspace, sink,
NULL);
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