Revert "Revert "Implement libvlc_video_get_size(), close #3679""

This reverts commit 47cf242f.

lib/video.c

@@ -161,18 +161,22 @@ libvlc_video_take_snapshot( libvlc_media_player_t *p_mi, unsigned num,
 int libvlc_video_get_size( libvlc_media_player_t *p_mi, unsigned num,
                            unsigned *restrict px, unsigned *restrict py )
 {
-#if 0
-    vout_thread_t *p_vout = GetVout (p_mi, num);
-    if (p_vout == NULL)
-        return -1;
+    libvlc_media_track_info_t *info;
+    int ret = -1;
+    int infos = libvlc_media_get_tracks_info(p_mi->p_md, &info);
+    if (infos <= 0)
+        return ret;
+
+    for (int i = 0; i < infos; i++)
+        if (info[i].i_type == libvlc_track_video && num-- == 0) {
+            *px = info[i].u.video.i_width;
+            *py = info[i].u.video.i_height;
+            ret = 0;
+            break;
+        }
 
-    *px = p_vout->i_window_height;
-    *py = p_vout->i_window_width;
-    vlc_object_release (p_vout);
-    return 0;
-#else
-    return -1;
-#endif
+    free(info);
+    return ret;
 }
 
 int libvlc_video_get_height( libvlc_media_player_t *p_mi )