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docs: Added metadata design doc
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Thibault Saunier
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docs/design/metadata.txt
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263
docs/design/metadata.txt
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Metadata
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~~~~~~~~
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Summary
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~~~~~~~
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1. Basic ideas
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2. Problems
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3. Ways of solving problems
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4. Use-cases
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5. API draft
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1. Basic ideas
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~~~~~~~~~~~~~~
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If we look at entities that are present in GES we can see that almost all of
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them need some sort of metadata:
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* GESTimeline
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* GESTimelineLayer
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* GESTimelineObject
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* GESTrackObject
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* Yet to be implemented GESProject
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For all those classes to be able to contain metadatas and to avoid code
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duplication as much as possible, we should have an interface to handle Metadata.
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Let's call the interface GESMetaContainer for now (name to be defined).
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2. Problems
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~~~~~~~~~~~
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1) We must be able to discover all metadata items that are
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attached to object
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2) We must be able to hold metadata of any type user wants
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3) Some metadatas are read only, others are writable
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4) User should be able to query metadata easily using various criteria
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5) Metadatas should be serializable
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6) User should be able to define read only metadatas with a default value
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7) User should be able to define metadatas that have a specific type which can not
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be changed when setting a new value
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3. Possible solution
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~~~~~~~~~~~~~~~~~~~~~
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1) To implement metadata GstStructure will be used. It allows to get list of
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all available tags in specified list by calling "gst_structure_foreach".
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2) We will have methods to register metas
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4. Use-cases
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~~~~~~~~~~~~
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UC-1. Hold tag information about file source asset.
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- TS: I think some of them are TrackObject specific... so we should be
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able to get them from the 2 types of objects
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UC-2. Hold descriptions of operations
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UC-3. Hold information about projects (title, author, description)
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UC-4. Hold user comments about any of TimelineLayer/Timeline/Project/TimelineObjects
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UC-5. Hold application specific settings (i.e. layer height, folding state
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in PiTiVi)
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UC-6. Serialize a timeline, project and keep metadatas
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5. API
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~~~~~~
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We have a GESMetdata class that controls metadata.
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gboolean
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ges_meta_container_set_boolean (GESMetaContainer *container,
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const gchar* meta_item,
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gboolean value);
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gboolean
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ges_meta_container_set_int (GESMetaContainer *container,
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const gchar* meta_item,
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gint value);
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gboolean
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ges_meta_container_set_uint (GESMetaContainer *container,
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const gchar* meta_item,
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guint value);
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gboolean
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ges_meta_container_set_int64 (GESMetaContainer *container,
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const gchar* meta_item,
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gint64 value);
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gboolean
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ges_meta_container_set_uint64 (GESMetaContainer *container,
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const gchar* meta_item,
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guint64 value);
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gboolean
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ges_meta_container_set_float (GESMetaContainer *container,
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const gchar* meta_item,
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gfloat value);
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gboolean
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ges_meta_container_set_double (GESMetaContainer *container,
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const gchar* meta_item,
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gdouble value);
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gboolean
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ges_meta_container_set_date (GESMetaContainer *container,
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const gchar* meta_item,
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const GDate* value);
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gboolean
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ges_meta_container_set_date_time (GESMetaContainer *container,
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const gchar* meta_item,
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const GstDateTime* value);
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gboolean
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ges_meta_container_set_string (GESMetaContainer *container,
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const gchar* meta_item,
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const gchar* value);
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gboolean
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ges_meta_container_set_meta (GESMetaContainer * container,
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const gchar* meta_item,
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const GValue *value);
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gboolean
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ges_meta_container_register_meta_boolean (GESMetaContainer *container,
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GESMetaFlag flags,
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const gchar* meta_item,
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gboolean value);
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gboolean
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ges_meta_container_register_meta_int (GESMetaContainer *container,
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GESMetaFlag flags,
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const gchar* meta_item,
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gint value);
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gboolean
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ges_meta_container_register_meta_uint (GESMetaContainer *container,
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GESMetaFlag flags,
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const gchar* meta_item,
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guint value);
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gboolean
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ges_meta_container_register_meta_int64 (GESMetaContainer *container,
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GESMetaFlag flags,
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const gchar* meta_item,
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gint64 value);
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gboolean
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ges_meta_container_register_meta_uint64 (GESMetaContainer *container,
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GESMetaFlag flags,
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const gchar* meta_item,
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guint64 value);
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gboolean
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ges_meta_container_register_meta_float (GESMetaContainer *container,
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GESMetaFlag flags,
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const gchar* meta_item,
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gfloat value);
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gboolean
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ges_meta_container_register_meta_double (GESMetaContainer *container,
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GESMetaFlag flags,
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const gchar* meta_item,
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gdouble value);
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gboolean
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ges_meta_container_register_meta_date (GESMetaContainer *container,
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GESMetaFlag flags,
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const gchar* meta_item,
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const GDate* value);
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gboolean
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ges_meta_container_register_meta_date_time (GESMetaContainer *container,
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GESMetaFlag flags,
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const gchar* meta_item,
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const GstDateTime* value);
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gboolean
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ges_meta_container_register_meta_string (GESMetaContainer *container,
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GESMetaFlag flags,
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const gchar* meta_item,
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const gchar* value);
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gboolean
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ges_meta_container_register_meta (GESMetaContainer *container,
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GESMetaFlag flags,
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const gchar* meta_item,
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const GValue * value);
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gboolean
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ges_meta_container_check_meta_registered (GESMetaContainer *container,
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const gchar * meta_item,
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GESMetaFlag * flags,
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GType * type);
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gboolean
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ges_meta_container_get_boolean (GESMetaContainer *container,
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const gchar* meta_item,
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gboolean* dest);
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gboolean
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ges_meta_container_get_int (GESMetaContainer *container,
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const gchar* meta_item,
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gint* dest);
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gboolean
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ges_meta_container_get_uint (GESMetaContainer *container,
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const gchar* meta_item,
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guint* dest);
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gboolean
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ges_meta_container_get_int64 (GESMetaContainer *container,
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const gchar* meta_item,
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gint64* dest);
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gboolean
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ges_meta_container_get_uint64 (GESMetaContainer *container,
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const gchar* meta_item,
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guint64* dest);
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gboolean
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ges_meta_container_get_float (GESMetaContainer *container,
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const gchar* meta_item,
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gfloat* dest);
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gboolean
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ges_meta_container_get_double (GESMetaContainer *container,
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const gchar* meta_item,
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gdouble* dest);
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gboolean
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ges_meta_container_get_date (GESMetaContainer *container,
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const gchar* meta_item,
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GDate** dest);
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gboolean
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ges_meta_container_get_date_time (GESMetaContainer *container,
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const gchar* meta_item,
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GstDateTime** dest);
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const gchar *
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ges_meta_container_get_string (GESMetaContainer * container,
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const gchar * meta_item);
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const GValue *
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ges_meta_container_get_meta (GESMetaContainer * container,
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const gchar * key);
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typedef void
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(*GESMetaForeachFunc) (const GESMetaContainer *container,
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const gchar *key,
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const GValue *value,
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gpointer user_data);
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void
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ges_meta_container_foreach (GESMetaContainer *container,
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GESMetaForeachFunc func,
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gpointer user_data);
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gchar *
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ges_meta_container_metas_to_string (GESMetaContainer *container);
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gboolean
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ges_meta_container_add_metas_from_string (GESMetaContainer *container,
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const gchar *str);
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