Re: LuaJIT FFI/GStreamer?

[Daurnimator <quae@...>]

You can't do this with the FFI yet; there is no callback support.
I'm using ffmpeg instead; try test.lua in https://github.com/daurnimator/lomp2/

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
>