4363ace07f0bf763a70dad441d66a7ab48134b9b
[vlc.git] / src / control / media_descriptor.c
1 /*****************************************************************************
2  * media_descriptor.c: Libvlc API media descripor management
3  *****************************************************************************
4  * Copyright (C) 2007 the VideoLAN team
5  * $Id$
6  *
7  * Authors: Pierre d'Herbemont <pdherbemont@videolan.org>
8  *
9  * This program is free software; you can redistribute it and/or modify
10  * it under the terms of the GNU General Public License as published by
11  * the Free Software Foundation; either version 2 of the License, or
12  * (at your option) any later version.
13  *
14  * This program is distributed in the hope that it will be useful,
15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
17  * GNU General Public License for more details.
18  *
19  * You should have received a copy of the GNU General Public License
20  * along with this program; if not, write to the Free Software
21  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
22  *****************************************************************************/
23
24 #include "libvlc_internal.h"
25
26 #include <vlc/libvlc.h>
27 #include <vlc_input.h>
28 #include <vlc_meta.h>
29
30 /* For the preparser */
31 #include <vlc_playlist.h>
32
33 static const vlc_meta_type_t libvlc_to_vlc_meta[] =
34 {
35     [libvlc_meta_Title]        = vlc_meta_Title,
36     [libvlc_meta_Artist]       = vlc_meta_Artist,
37     [libvlc_meta_Genre]        = vlc_meta_Genre,
38     [libvlc_meta_Copyright]    = vlc_meta_Copyright,
39     [libvlc_meta_Album]        = vlc_meta_Album,
40     [libvlc_meta_TrackNumber]  = vlc_meta_TrackNumber,
41     [libvlc_meta_Description]  = vlc_meta_Description,
42     [libvlc_meta_Rating]       = vlc_meta_Rating,
43     [libvlc_meta_Date]         = vlc_meta_Date,
44     [libvlc_meta_Setting]      = vlc_meta_Setting,
45     [libvlc_meta_URL]          = vlc_meta_URL,
46     [libvlc_meta_Language]     = vlc_meta_Language,
47     [libvlc_meta_NowPlaying]   = vlc_meta_NowPlaying,
48     [libvlc_meta_Publisher]    = vlc_meta_Publisher,
49     [libvlc_meta_EncodedBy]    = vlc_meta_EncodedBy,
50     [libvlc_meta_ArtworkURL]   = vlc_meta_ArtworkURL,
51     [libvlc_meta_TrackID]      = vlc_meta_TrackID
52 };
53
54 static const libvlc_meta_t vlc_to_libvlc_meta[] =
55 {
56     [vlc_meta_Title]        = libvlc_meta_Title,
57     [vlc_meta_Artist]       = libvlc_meta_Artist,
58     [vlc_meta_Genre]        = libvlc_meta_Genre,
59     [vlc_meta_Copyright]    = libvlc_meta_Copyright,
60     [vlc_meta_Album]        = libvlc_meta_Album,
61     [vlc_meta_TrackNumber]  = libvlc_meta_TrackNumber,
62     [vlc_meta_Description]  = libvlc_meta_Description,
63     [vlc_meta_Rating]       = libvlc_meta_Rating,
64     [vlc_meta_Date]         = libvlc_meta_Date,
65     [vlc_meta_Setting]      = libvlc_meta_Setting,
66     [vlc_meta_URL]          = libvlc_meta_URL,
67     [vlc_meta_Language]     = libvlc_meta_Language,
68     [vlc_meta_NowPlaying]   = libvlc_meta_NowPlaying,
69     [vlc_meta_Publisher]    = libvlc_meta_Publisher,
70     [vlc_meta_EncodedBy]    = libvlc_meta_EncodedBy,
71     [vlc_meta_ArtworkURL]   = libvlc_meta_ArtworkURL,
72     [vlc_meta_TrackID]      = libvlc_meta_TrackID
73 };
74
75 /**************************************************************************
76  * input_item_subitem_added (Private) (vlc event Callback)
77  **************************************************************************/
78 static void input_item_subitem_added( const vlc_event_t *p_event,
79                                        void * user_data )
80 {
81     libvlc_media_descriptor_t * p_md = user_data;
82     libvlc_media_descriptor_t * p_md_child;
83     libvlc_event_t event;
84
85     p_md_child = libvlc_media_descriptor_new_from_input_item(
86                 p_md->p_libvlc_instance,
87                 p_event->u.input_item_subitem_added.p_new_child, NULL );
88
89     /* Add this to our media list */
90     if( !p_md->p_subitems )
91     {
92         p_md->p_subitems = libvlc_media_list_new( p_md->p_libvlc_instance, NULL );
93         libvlc_media_list_set_media_descriptor( p_md->p_subitems, p_md, NULL );
94     }
95     if( p_md->p_subitems )
96     {
97         libvlc_media_list_add_media_descriptor( p_md->p_subitems, p_md_child, NULL );
98     }
99
100     /* Construct the event */
101     event.type = libvlc_MediaDescriptorSubItemAdded;
102     event.u.media_descriptor_subitem_added.new_child = p_md_child;
103
104     /* Send the event */
105     libvlc_event_send( p_md->p_event_manager, &event );
106     libvlc_media_descriptor_release( p_md_child );
107 }
108
109 /**************************************************************************
110  * input_item_meta_changed (Private) (vlc event Callback)
111  **************************************************************************/
112 static void input_item_meta_changed( const vlc_event_t *p_event,
113                                      void * user_data )
114 {
115     libvlc_media_descriptor_t * p_md = user_data;
116     libvlc_event_t event;
117
118     /* Construct the event */
119     event.type = libvlc_MediaDescriptorMetaChanged;
120     event.u.media_descriptor_meta_changed.meta_type =
121         vlc_to_libvlc_meta[p_event->u.input_item_meta_changed.meta_type];
122
123     /* Send the event */
124     libvlc_event_send( p_md->p_event_manager, &event );
125 }
126
127 /**************************************************************************
128  * input_item_duration_changed (Private) (vlc event Callback)
129  **************************************************************************/
130 static void input_item_duration_changed( const vlc_event_t *p_event,
131                                          void * user_data )
132 {
133     libvlc_media_descriptor_t * p_md = user_data;
134     libvlc_event_t event;
135
136     /* Construct the event */
137     event.type = libvlc_MediaDescriptorDurationChanged;
138     event.u.media_descriptor_duration_changed.new_duration = 
139         p_event->u.input_item_duration_changed.new_duration;
140
141     /* Send the event */
142     libvlc_event_send( p_md->p_event_manager, &event );
143 }
144
145 /**************************************************************************
146  * input_item_preparsed_changed (Private) (vlc event Callback)
147  **************************************************************************/
148 static void input_item_preparsed_changed( const vlc_event_t *p_event,
149                                           void * user_data )
150 {
151     libvlc_media_descriptor_t * p_md = user_data;
152     libvlc_event_t event;
153
154     /* Construct the event */
155     event.type = libvlc_MediaDescriptorPreparsedChanged;
156     event.u.media_descriptor_preparsed_changed.new_status = 
157         p_event->u.input_item_preparsed_changed.new_status;
158
159     /* Send the event */
160     libvlc_event_send( p_md->p_event_manager, &event );
161 }
162
163 /**************************************************************************
164  * Install event handler (Private)
165  **************************************************************************/
166 static void install_input_item_observer( libvlc_media_descriptor_t *p_md )
167 {
168     vlc_event_attach( &p_md->p_input_item->event_manager,
169                       vlc_InputItemSubItemAdded,
170                       input_item_subitem_added,
171                       p_md );
172     vlc_event_attach( &p_md->p_input_item->event_manager,
173                       vlc_InputItemMetaChanged,
174                       input_item_meta_changed,
175                       p_md );
176     vlc_event_attach( &p_md->p_input_item->event_manager,
177                       vlc_InputItemDurationChanged,
178                       input_item_duration_changed,
179                       p_md );
180     vlc_event_attach( &p_md->p_input_item->event_manager,
181                       vlc_InputItemPreparsedChanged,
182                       input_item_preparsed_changed,
183                       p_md );
184 }
185
186 /**************************************************************************
187  * Uninstall event handler (Private)
188  **************************************************************************/
189 static void uninstall_input_item_observer( libvlc_media_descriptor_t *p_md )
190 {
191     vlc_event_detach( &p_md->p_input_item->event_manager,
192                       vlc_InputItemSubItemAdded,
193                       input_item_subitem_added,
194                       p_md );
195     vlc_event_detach( &p_md->p_input_item->event_manager,
196                       vlc_InputItemMetaChanged,
197                       input_item_meta_changed,
198                       p_md );
199     vlc_event_detach( &p_md->p_input_item->event_manager,
200                       vlc_InputItemDurationChanged,
201                       input_item_duration_changed,
202                       p_md );
203     vlc_event_detach( &p_md->p_input_item->event_manager,
204                       vlc_InputItemPreparsedChanged,
205                       input_item_preparsed_changed,
206                       p_md );
207 }
208
209 /**************************************************************************
210  * Preparse if not already done (Private)
211  **************************************************************************/
212 static void preparse_if_needed( libvlc_media_descriptor_t *p_md )
213 {
214     /* XXX: need some locking here */
215     if (!p_md->b_preparsed)
216     {
217         playlist_PreparseEnqueue(
218                 p_md->p_libvlc_instance->p_libvlc_int->p_playlist,
219                 p_md->p_input_item );
220         p_md->b_preparsed = VLC_TRUE;
221     }
222 }
223
224 /**************************************************************************
225  * Create a new media descriptor object from an input_item
226  * (libvlc internal)
227  * That's the generic constructor
228  **************************************************************************/
229 libvlc_media_descriptor_t * libvlc_media_descriptor_new_from_input_item(
230                                    libvlc_instance_t *p_instance,
231                                    input_item_t *p_input_item,
232                                    libvlc_exception_t *p_e )
233 {
234     libvlc_media_descriptor_t * p_md;
235
236     if (!p_input_item)
237     {
238         libvlc_exception_raise( p_e, "No input item given" );
239         return NULL;
240     }
241
242     p_md = malloc( sizeof(libvlc_media_descriptor_t) );
243     p_md->p_libvlc_instance = p_instance;
244     p_md->p_input_item      = p_input_item;
245     p_md->b_preparsed       = VLC_FALSE;
246     p_md->i_refcount        = 1;
247     p_md->p_user_data       = NULL;
248
249     p_md->state = libvlc_NothingSpecial;
250
251     /* A media descriptor can be a playlist. When you open a playlist
252      * It can give a bunch of item to read. */
253     p_md->p_subitems        = NULL;
254
255     vlc_dictionary_init( &p_md->tags, 1 );
256
257     p_md->p_event_manager = libvlc_event_manager_new( p_md, p_instance, p_e );
258     libvlc_event_manager_register_event_type( p_md->p_event_manager,
259         libvlc_MediaDescriptorMetaChanged, p_e );
260     libvlc_event_manager_register_event_type( p_md->p_event_manager,
261         libvlc_MediaDescriptorSubItemAdded, p_e );
262     libvlc_event_manager_register_event_type( p_md->p_event_manager,
263         libvlc_MediaDescriptorFreed, p_e );
264     libvlc_event_manager_register_event_type( p_md->p_event_manager,
265         libvlc_MediaDescriptorDurationChanged, p_e );
266     libvlc_event_manager_register_event_type( p_md->p_event_manager,
267         libvlc_MediaDescriptorStateChanged, p_e );
268
269     vlc_gc_incref( p_md->p_input_item );
270
271     install_input_item_observer( p_md );
272
273     return p_md;
274 }
275
276 /**************************************************************************
277  * Create a new media descriptor object
278  **************************************************************************/
279 libvlc_media_descriptor_t * libvlc_media_descriptor_new(
280                                    libvlc_instance_t *p_instance,
281                                    const char * psz_mrl,
282                                    libvlc_exception_t *p_e )
283 {
284     input_item_t * p_input_item;
285     libvlc_media_descriptor_t * p_md;
286
287     p_input_item = input_ItemNew( p_instance->p_libvlc_int, psz_mrl, NULL );
288
289     if (!p_input_item)
290     {
291         libvlc_exception_raise( p_e, "Can't create md's input_item" );
292         return NULL;
293     }
294
295     p_md = libvlc_media_descriptor_new_from_input_item( p_instance,
296                 p_input_item, p_e );
297
298     /* The p_input_item is retained in libvlc_media_descriptor_new_from_input_item */
299     vlc_gc_decref( p_input_item );
300     
301     return p_md;
302 }
303
304 /**************************************************************************
305  * Create a new media descriptor object
306  **************************************************************************/
307 libvlc_media_descriptor_t * libvlc_media_descriptor_new_as_node(
308                                    libvlc_instance_t *p_instance,
309                                    const char * psz_name,
310                                    libvlc_exception_t *p_e )
311 {
312     input_item_t * p_input_item;
313     libvlc_media_descriptor_t * p_md;
314
315     p_input_item = input_ItemNew( p_instance->p_libvlc_int, "vlc:nop", psz_name );
316
317     if (!p_input_item)
318     {
319         libvlc_exception_raise( p_e, "Can't create md's input_item" );
320         return NULL;
321     }
322
323     p_md = libvlc_media_descriptor_new_from_input_item( p_instance,
324                 p_input_item, p_e );
325
326     p_md->p_subitems = libvlc_media_list_new( p_md->p_libvlc_instance, NULL );
327
328     return p_md;
329 }
330
331 /**************************************************************************
332  * Add an option to the media descriptor,
333  * that will be used to determine how the media_instance will read the
334  * media_descriptor. This allow to use VLC advanced reading/streaming
335  * options in a per-media basis
336  *
337  * The options are detailled in vlc --long-help, for instance "--sout-all"
338  **************************************************************************/
339 void libvlc_media_descriptor_add_option(
340                                    libvlc_media_descriptor_t * p_md,
341                                    const char * ppsz_option,
342                                    libvlc_exception_t *p_e )
343 {
344     (void)p_e;
345     input_ItemAddOptionNoDup( p_md->p_input_item, ppsz_option );
346 }
347
348 /**************************************************************************
349  * Delete a media descriptor object
350  **************************************************************************/
351 void libvlc_media_descriptor_release( libvlc_media_descriptor_t *p_md )
352 {
353     int i;
354     if (!p_md)
355         return;
356
357     p_md->i_refcount--;
358
359     if( p_md->i_refcount > 0 )
360         return;
361
362     if( p_md->p_subitems )
363         libvlc_media_list_release( p_md->p_subitems );
364
365     uninstall_input_item_observer( p_md );
366     vlc_gc_decref( p_md->p_input_item );
367
368     /* Construct the event */
369     libvlc_event_t event;
370     event.type = libvlc_MediaDescriptorFreed;
371     event.u.media_descriptor_freed.md = p_md;
372
373     /* Send the event */
374     libvlc_event_send( p_md->p_event_manager, &event );
375
376     libvlc_event_manager_release( p_md->p_event_manager );
377
378     char ** all_keys = vlc_dictionary_all_keys( &p_md->tags );
379     for( i = 0; all_keys[i]; i++ )
380     {
381         int j;
382         struct libvlc_tags_storage_t * p_ts = vlc_dictionary_value_for_key( &p_md->tags, all_keys[i] );
383         for( j = 0; j < p_ts->i_count; j++ )
384         {
385             free( p_ts->ppsz_tags[j] );
386             free( p_ts->ppsz_tags );
387         }
388         free( p_ts );
389     }
390     vlc_dictionary_clear( &p_md->tags );
391     free( p_md );
392 }
393
394 /**************************************************************************
395  * Retain a media descriptor object
396  **************************************************************************/
397 void libvlc_media_descriptor_retain( libvlc_media_descriptor_t *p_md )
398 {
399     if (!p_md)
400         return;
401
402     p_md->i_refcount++;
403 }
404
405 /**************************************************************************
406  * Duplicate a media descriptor object
407  **************************************************************************/
408 libvlc_media_descriptor_t *
409 libvlc_media_descriptor_duplicate( libvlc_media_descriptor_t *p_md_orig )
410 {
411     return libvlc_media_descriptor_new_from_input_item(
412         p_md_orig->p_libvlc_instance, p_md_orig->p_input_item, NULL );
413 }
414
415 /**************************************************************************
416  * Retain a media descriptor object
417  **************************************************************************/
418 char *
419 libvlc_media_descriptor_get_mrl( libvlc_media_descriptor_t * p_md,
420                                  libvlc_exception_t * p_e )
421 {
422     (void)p_e;
423     return input_item_GetURI( p_md->p_input_item );
424 }
425
426 /**************************************************************************
427  * Getter for meta information
428  **************************************************************************/
429
430 char * libvlc_media_descriptor_get_meta( libvlc_media_descriptor_t *p_md,
431                                          libvlc_meta_t e_meta,
432                                          libvlc_exception_t *p_e )
433 {
434     VLC_UNUSED(p_e);
435
436     char * psz_meta;
437
438     /* XXX: locking */
439
440     preparse_if_needed( p_md );
441
442     psz_meta = input_item_GetMeta( p_md->p_input_item,
443                                    libvlc_to_vlc_meta[e_meta] );
444     
445     if( e_meta == libvlc_meta_ArtworkURL && !psz_meta )
446     {
447         playlist_AskForArtEnqueue(
448                 p_md->p_libvlc_instance->p_libvlc_int->p_playlist,
449                 p_md->p_input_item );
450     }
451
452     /* Should be integrated in core */
453     if( !psz_meta && e_meta == libvlc_meta_Title && p_md->p_input_item->psz_name )
454     {
455         free( psz_meta );
456         return strdup( p_md->p_input_item->psz_name );
457     }
458
459     return psz_meta;
460 }
461
462 /**************************************************************************
463  * Getter for state information
464  * Can be error, playing, buffering, NothingSpecial.
465  **************************************************************************/
466
467 libvlc_state_t
468 libvlc_media_descriptor_get_state( libvlc_media_descriptor_t *p_md,
469                                    libvlc_exception_t *p_e )
470 {
471     (void)p_e;
472     return p_md->state;
473 }
474
475 /**************************************************************************
476  * Setter for state information (LibVLC Internal)
477  **************************************************************************/
478
479 void
480 libvlc_media_descriptor_set_state( libvlc_media_descriptor_t *p_md,
481                                    libvlc_state_t state,
482                                    libvlc_exception_t *p_e )
483 {
484     (void)p_e;
485     libvlc_event_t event;
486
487     p_md->state = state;
488
489     /* Construct the event */
490     event.type = libvlc_MediaDescriptorStateChanged;
491     event.u.media_descriptor_state_changed.new_state = state;
492
493     /* Send the event */
494     libvlc_event_send( p_md->p_event_manager, &event );
495 }
496
497 /**************************************************************************
498  * Add a tag
499  **************************************************************************/
500 void libvlc_media_descriptor_add_tag( libvlc_media_descriptor_t *p_md,
501                                       const char * key,
502                                       const libvlc_tag_t tag,
503                                       libvlc_exception_t *p_e )
504 {
505     VLC_UNUSED(p_e);
506
507     struct libvlc_tags_storage_t * p_ts;
508
509     if( !tag || !key )
510         return;
511  
512     p_ts = vlc_dictionary_value_for_key( &p_md->tags, key );
513
514     if( !p_ts )
515     {
516         p_ts = malloc(sizeof(struct libvlc_tags_storage_t));
517         memset( p_ts, 0, sizeof(struct libvlc_tags_storage_t) );
518     }
519     p_ts->i_count++;
520
521     if( !p_ts->ppsz_tags )
522         p_ts->ppsz_tags = malloc(sizeof(char*)*(p_ts->i_count));
523     else
524         p_ts->ppsz_tags = realloc(p_ts->ppsz_tags, sizeof(char*)*(p_ts->i_count));
525  
526     p_ts->ppsz_tags[p_ts->i_count-1] = strdup( tag );
527 }
528
529
530 /**************************************************************************
531  * Remove a tag
532  **************************************************************************/
533 void libvlc_media_descriptor_remove_tag( libvlc_media_descriptor_t *p_md,
534                                          const char * key,
535                                          const libvlc_tag_t tag,
536                                          libvlc_exception_t *p_e )
537 {
538     VLC_UNUSED(p_e);
539
540     struct libvlc_tags_storage_t * p_ts;
541     int i;
542
543     if( !tag || !key )
544         return;
545  
546     p_ts = vlc_dictionary_value_for_key( &p_md->tags, key );
547
548     if( !p_ts )
549         return;
550
551     for( i = 0; i < p_ts->i_count; i++ )
552     {
553         if( !strcmp( p_ts->ppsz_tags[i], tag ) )
554         {
555             free( p_ts->ppsz_tags[i] );
556             memcpy( p_ts->ppsz_tags + i + 1, p_ts->ppsz_tags + i, (p_ts->i_count - i - 2)*sizeof(char*) );
557             /* Don't dealloc, the memory will be regain if we add a new tag */
558             p_ts->i_count--;
559             return;
560         }
561     }
562 }
563
564 /**************************************************************************
565  * Get tags count
566  **************************************************************************/
567 int libvlc_media_descriptor_tags_count_for_key( libvlc_media_descriptor_t *p_md,
568                                                  const char * key,
569                                                  libvlc_exception_t *p_e )
570 {
571     VLC_UNUSED(p_e);
572
573     struct libvlc_tags_storage_t * p_ts;
574
575     if( !key )
576         return 0;
577  
578     p_ts = vlc_dictionary_value_for_key( &p_md->tags, key );
579
580     if( !p_ts )
581         return 0;
582     return p_ts->i_count;
583 }
584
585 /**************************************************************************
586  * Get a tag
587  **************************************************************************/
588 libvlc_tag_t
589 libvlc_media_descriptor_tag_at_index_for_key( libvlc_media_descriptor_t *p_md,
590                                               int i,
591                                               const char * key,
592                                               libvlc_exception_t *p_e )
593 {
594     VLC_UNUSED(p_e);
595
596     struct libvlc_tags_storage_t * p_ts;
597
598     if( !key )
599         return NULL;
600  
601     p_ts = vlc_dictionary_value_for_key( &p_md->tags, key );
602
603     if( !p_ts )
604         return NULL;
605  
606     return strdup( p_ts->ppsz_tags[i] );
607 }
608
609 /**************************************************************************
610  * subitems
611  **************************************************************************/
612 libvlc_media_list_t *
613 libvlc_media_descriptor_subitems( libvlc_media_descriptor_t * p_md,
614                                   libvlc_exception_t * p_e )
615 {
616     VLC_UNUSED(p_e);
617
618     if( p_md->p_subitems )
619         libvlc_media_list_retain( p_md->p_subitems );
620     return p_md->p_subitems;
621 }
622
623 /**************************************************************************
624  * event_manager
625  **************************************************************************/
626 libvlc_event_manager_t *
627 libvlc_media_descriptor_event_manager( libvlc_media_descriptor_t * p_md,
628                                        libvlc_exception_t * p_e )
629 {
630     VLC_UNUSED(p_e);
631
632     return p_md->p_event_manager;
633 }
634
635 /**************************************************************************
636  * Get duration of media_descriptor object.
637  **************************************************************************/
638 vlc_int64_t
639 libvlc_media_descriptor_get_duration( libvlc_media_descriptor_t * p_md,
640                                       libvlc_exception_t * p_e )
641 {
642     VLC_UNUSED(p_e);
643
644     if( p_md && p_md->p_input_item)
645     {
646         return input_item_GetDuration( p_md->p_input_item );
647     }
648     else
649     {
650         return -1;
651     }
652 }
653
654 /**************************************************************************
655  * Get preparsed status for media_descriptor object.
656  **************************************************************************/
657 vlc_bool_t
658 libvlc_media_descriptor_is_preparsed( libvlc_media_descriptor_t * p_md,
659                                        libvlc_exception_t * p_e )
660 {
661     VLC_UNUSED(p_e);
662
663     if( p_md && p_md->p_input_item)
664     {
665         return input_item_IsPreparsed( p_md->p_input_item );
666     }
667     else
668     {
669         return VLC_FALSE;
670     }
671 }
672
673 /**************************************************************************
674  * Sets media descriptor's user_data. user_data is specialized data 
675  * accessed by the host application, VLC.framework uses it as a pointer to 
676  * an native object that references a libvlc_media_descriptor_t pointer
677  **************************************************************************/
678 void 
679 libvlc_media_descriptor_set_user_data( libvlc_media_descriptor_t * p_md,
680                                        void * p_new_user_data,
681                                        libvlc_exception_t * p_e )
682 {
683     VLC_UNUSED(p_e);
684
685     if( p_md )
686     {
687         p_md->p_user_data = p_new_user_data;
688     }
689 }
690
691 /**************************************************************************
692  * Get media descriptor's user_data. user_data is specialized data 
693  * accessed by the host application, VLC.framework uses it as a pointer to 
694  * an native object that references a libvlc_media_descriptor_t pointer
695  **************************************************************************/
696 void *
697 libvlc_media_descriptor_get_user_data( libvlc_media_descriptor_t * p_md,
698                                        libvlc_exception_t * p_e )
699 {
700     VLC_UNUSED(p_e);
701
702     if( p_md )
703     {
704         return p_md->p_user_data;
705     }
706     else
707     {
708         return NULL;
709     }
710 }
711