controlled properties

Controlled properties offers a lightweight way to adjust gobject properties over stream-time. It works by using time-stamped value pairs that are queued for element-properties. At run-time the elements continously pull values changes for the current stream-time.

What needs to be changed in a GstElement? Very little - it is just two steps to make a plugin controllable!

What needs to be done in applications? Again its not a lot to change.

struct GstObject

struct GstObject {
  GMutex         lock;        /* object LOCK */
  gchar         *name;        /* object name */
  GstObject     *parent;      /* this object's parent, weak ref */
  guint32        flags;
};

GStreamer base object class.

struct GstObjectClass

struct GstObjectClass {
  GInitiallyUnownedClass parent_class;

  const gchar *path_string_separator;

  /* signals */
  void          (*deep_notify)      (GstObject * object, GstObject * orig, GParamSpec * pspec);

  /* virtual methods for subclasses */
};

GStreamer base object class.

enum GstObjectFlags

typedef enum {
  /* padding */
  GST_OBJECT_FLAG_LAST = (1<<4)
} GstObjectFlags;

The standard flags that an gstobject may have.

GST_OBJECT_FLAGS()

#define GST_OBJECT_FLAGS(obj)                  (GST_OBJECT_CAST (obj)->flags)

This macro returns the entire set of flags for the object.

GST_OBJECT_FLAG_IS_SET()

#define GST_OBJECT_FLAG_IS_SET(obj,flag)       ((GST_OBJECT_FLAGS (obj) & (flag)) == (flag))

This macro checks to see if the given flag is set.

GST_OBJECT_FLAG_SET()

#define GST_OBJECT_FLAG_SET(obj,flag)          (GST_OBJECT_FLAGS (obj) |= (flag))

This macro sets the given bits.

GST_OBJECT_FLAG_UNSET()

#define GST_OBJECT_FLAG_UNSET(obj,flag)        (GST_OBJECT_FLAGS (obj) &= ~(flag))

This macro usets the given bits.

GST_OBJECT_NAME()

#define GST_OBJECT_NAME(obj)            (GST_OBJECT_CAST(obj)->name)

Get the name of this object

GST_OBJECT_PARENT()

#define GST_OBJECT_PARENT(obj)          (GST_OBJECT_CAST(obj)->parent)

Get the parent of this object

GST_OBJECT_REFCOUNT()

#define GST_OBJECT_REFCOUNT(obj)                (((GObject*)(obj))->ref_count)

Get access to the reference count field of the object.

GST_OBJECT_REFCOUNT_VALUE()

#define GST_OBJECT_REFCOUNT_VALUE(obj)          g_atomic_int_get ((gint *) &GST_OBJECT_REFCOUNT(obj))

Get the reference count value of the object.

GST_OBJECT_LOCK()

#define GST_OBJECT_LOCK(obj)                   g_mutex_lock(GST_OBJECT_GET_LOCK(obj))

This macro will obtain a lock on the object, making serialization possible. It blocks until the lock can be obtained.

GST_OBJECT_TRYLOCK()

#define GST_OBJECT_TRYLOCK(obj)                g_mutex_trylock(GST_OBJECT_GET_LOCK(obj))

This macro will try to obtain a lock on the object, but will return with FALSE if it can't get it immediately.

GST_OBJECT_UNLOCK()

#define GST_OBJECT_UNLOCK(obj)                 g_mutex_unlock(GST_OBJECT_GET_LOCK(obj))

This macro releases a lock on the object.

GST_OBJECT_GET_LOCK()

#define GST_OBJECT_GET_LOCK(obj)               (&GST_OBJECT_CAST(obj)->lock)

Acquire a reference to the mutex of this object.

gst_object_set_name ()

gboolean            gst_object_set_name                 (GstObject *object,
                                                         const gchar *name);

Sets the name of object, or gives object a guaranteed unique name (if name is NULL). This function makes a copy of the provided name, so the caller retains ownership of the name it sent.

gst_object_get_name ()

gchar *             gst_object_get_name                 (GstObject *object);

Returns a copy of the name of object. Caller should g_free() the return value after usage. For a nameless object, this returns NULL, which you can safely g_free() as well.

Free-function: g_free

gst_object_set_parent ()

gboolean            gst_object_set_parent               (GstObject *object,
                                                         GstObject *parent);

Sets the parent of object to parent. The object's reference count will be incremented, and any floating reference will be removed (see gst_object_ref_sink()).

gst_object_get_parent ()

GstObject *         gst_object_get_parent               (GstObject *object);

Returns the parent of object. This function increases the refcount of the parent object so you should gst_object_unref() it after usage.

gst_object_unparent ()

void                gst_object_unparent                 (GstObject *object);

Clear the parent of object, removing the associated reference. This function decreases the refcount of object.

MT safe. Grabs and releases object's lock.

gst_object_default_deep_notify ()

void                gst_object_default_deep_notify      (GObject *object,
                                                         GstObject *orig,
                                                         GParamSpec *pspec,
                                                         gchar **excluded_props);

A default deep_notify signal callback for an object. The user data should contain a pointer to an array of strings that should be excluded from the notify. The default handler will print the new value of the property using g_print.

MT safe. This function grabs and releases object's LOCK for getting its path string.

gst_object_default_error ()

void                gst_object_default_error            (GstObject *source,
                                                         const GError *error,
                                                         const gchar *debug);

A default error function that uses g_printerr() to display the error message and the optional debug sting..

The default handler will simply print the error string using g_print.

gst_object_check_uniqueness ()

gboolean            gst_object_check_uniqueness         (GList *list,
                                                         const gchar *name);

Checks to see if there is any object named name in list. This function does not do any locking of any kind. You might want to protect the provided list with the lock of the owner of the list. This function will lock each GstObject in the list to compare the name, so be carefull when passing a list with a locked object.

gst_object_has_ancestor ()

gboolean            gst_object_has_ancestor             (GstObject *object,
                                                         GstObject *ancestor);

Check if object has an ancestor ancestor somewhere up in the hierarchy. One can e.g. check if a GstElement is inside a GstPipeline.

gst_object_ref ()

gpointer            gst_object_ref                      (gpointer object);

Increments the reference count on object. This function does not take the lock on object because it relies on atomic refcounting.

This object returns the input parameter to ease writing constructs like : result = gst_object_ref (object->parent);

gst_object_unref ()

void                gst_object_unref                    (gpointer object);

Decrements the reference count on object. If reference count hits zero, destroy object. This function does not take the lock on object as it relies on atomic refcounting.

The unref method should never be called with the LOCK held since this might deadlock the dispose function.

gst_object_ref_sink ()

gpointer            gst_object_ref_sink                 (gpointer object);

Increase the reference count of object, and possibly remove the floating reference, if object has a floating reference.

In other words, if the object is floating, then this call "assumes ownership" of the floating reference, converting it to a normal reference by clearing the floating flag while leaving the reference count unchanged. If the object is not floating, then this call adds a new normal reference increasing the reference count by one.

gst_object_replace ()

gboolean            gst_object_replace                  (GstObject **oldobj,
                                                         GstObject *newobj);

Atomically modifies a pointer to point to a new object. The reference count of oldobj is decreased and the reference count of newobj is increased.

Either newobj and the value pointed to by oldobj may be NULL.

gst_object_get_path_string ()

gchar *             gst_object_get_path_string          (GstObject *object);

Generates a string describing the path of object in the object hierarchy. Only useful (or used) for debugging.

Free-function: g_free

gst_object_suggest_next_sync ()

GstClockTime        gst_object_suggest_next_sync        (GstObject *object);

Returns a suggestion for timestamps where buffers should be split to get best controller results.

gst_object_sync_values ()

gboolean            gst_object_sync_values              (GstObject *object,
                                                         GstClockTime timestamp);

Sets the properties of the object, according to the GstControlSources that (maybe) handle them and for the given timestamp.

If this function fails, it is most likely the application developers fault. Most probably the control sources are not setup correctly.

gst_object_has_active_control_bindings ()

gboolean            gst_object_has_active_control_bindings
                                                        (GstObject *object);

Check if the object has an active controlled properties.

gst_object_set_control_bindings_disabled ()

void                gst_object_set_control_bindings_disabled
                                                        (GstObject *object,
                                                         gboolean disabled);

This function is used to disable all controlled properties of the object for some time, i.e. gst_object_sync_values() will do nothing.

gst_object_set_control_binding_disabled ()

void                gst_object_set_control_binding_disabled
                                                        (GstObject *object,
                                                         const gchar *property_name,
                                                         gboolean disabled);

This function is used to disable the GstController on a property for some time, i.e. gst_controller_sync_values() will do nothing for the property.

gst_object_add_control_binding ()

gboolean            gst_object_add_control_binding      (GstObject *object,
                                                         GstControlBinding *binding);

Sets the GstControlBinding. If there already was a GstControlBinding for this property it will be replaced. The object will take ownership of the binding.

gst_object_get_control_binding ()

GstControlBinding * gst_object_get_control_binding      (GstObject *object,
                                                         const gchar *property_name);

Gets the corresponding GstControlBinding for the property. This should be unreferenced again after use.

gst_object_remove_control_binding ()

gboolean            gst_object_remove_control_binding   (GstObject *object,
                                                         GstControlBinding *binding);

Removes the corresponding GstControlBinding. If it was the last ref of the binding, it will be disposed.

gst_object_get_value ()

GValue *            gst_object_get_value                (GstObject *object,
                                                         const gchar *property_name,
                                                         GstClockTime timestamp);

Gets the value for the given controlled property at the requested time.

gst_object_get_value_array ()

gboolean            gst_object_get_value_array          (GstObject *object,
                                                         const gchar *property_name,
                                                         GstClockTime timestamp,
                                                         GstClockTime interval,
                                                         guint n_values,
                                                         gpointer values);

Gets a number of values for the given controlled property starting at the requested time. The array values need to hold enough space for n_values of the same type as the objects property's type.

This function is useful if one wants to e.g. draw a graph of the control curve or apply a control curve sample by sample.

The values are unboxed and ready to be used. The similar function gst_object_get_g_value_array() returns the array as GValues and is better suites for bindings.

gst_object_get_g_value_array ()

gboolean            gst_object_get_g_value_array        (GstObject *object,
                                                         const gchar *property_name,
                                                         GstClockTime timestamp,
                                                         GstClockTime interval,
                                                         guint n_values,
                                                         GValue *values);

Gets a number of GValues for the given controlled property starting at the requested time. The array values need to hold enough space for n_values of GValue.

This function is useful if one wants to e.g. draw a graph of the control curve or apply a control curve sample by sample.

gst_object_get_control_rate ()

GstClockTime        gst_object_get_control_rate         (GstObject *object);

Obtain the control-rate for this object. Audio processing GstElement objects will use this rate to sub-divide their processing loop and call gst_object_sync_values() inbetween. The length of the processing segment should be up to control-rate nanoseconds.

If the object is not under property control, this will return GST_CLOCK_TIME_NONE. This allows the element to avoid the sub-dividing.

The control-rate is not expected to change if the element is in GST_STATE_PAUSED or GST_STATE_PLAYING.

gst_object_set_control_rate ()

void                gst_object_set_control_rate         (GstObject *object,
                                                         GstClockTime control_rate);

Change the control-rate for this object. Audio processing GstElement objects will use this rate to sub-divide their processing loop and call gst_object_sync_values() inbetween. The length of the processing segment should be up to control-rate nanoseconds.

The control-rate should not change if the element is in GST_STATE_PAUSED or GST_STATE_PLAYING.

The "name" property

  "name"                     gchar*                : Read / Write / Construct

The name of the object.

Default value: NULL

The "parent" property

  "parent"                   GstObject*            : Read / Write

The parent of the object.

The "deep-notify" signal

void                user_function                      (GstObject  *gstobject,
                                                        GstObject  *prop_object,
                                                        GParamSpec *prop,
                                                        gpointer    user_data)        : No Hooks

The deep notify signal is used to be notified of property changes. It is typically attached to the toplevel bin to receive notifications from all the elements contained in that bin.