On 27 October 2011 10:39, Ralf Van Bogaert <
pooshhmao@gmail.com> wrote:
> Hi list,
> This is my first post here, I've been using Lua for more than five years now
> for various personal and professional projects.
> I would like to incorporate Gstreamer in my project. There are a few
> libraries out there (such as lgob-gst) that support GStreamer, but they're
> either poorly documented, not supported anymore, or restricted in various
> ways.
> Now that I can make use of FFI in LuaJIT 2.0.0.8, I'm very much interested
> in trying to implement GStreamer this way. However I have next to no
> experience with C, and being a dyslexic ADD patient makes it hard for me to
> learn anything efficiently without a working example to dissect and mess
> around wiith.
> I have the following C example of constructing a basic GStreamer pipeline
> (
http://gstreamer.freedesktop.org/data/doc/gstreamer/head/manual/html/chapter-helloworld.html)
> #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;
> /* 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));
> 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);
> /* note that the demuxer will be linked to the decoder dynamically.
> The reason is that Ogg may contain various streams (for example
> audio and video). The source pad(s) will be created at run time,
> by the demuxer when it detects the amount and nature of streams.
> Therefore we connect a callback function which will be executed
> when the "pad-added" is emitted.*/
>
> /* 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));
> return 0;
> }
> What I would like to ask is if someone on this list could help me convert
> this to FFI.
> In practice, I don't think I even need the g_main_loop since I make use of
> the Qt framework instead of GTK.
> Thanks in advance and regards
> Ralf
>
