GstControlSource: GStreamer 1.0 Core Reference Manual

GstControlSource

GstControlSource — base class for control source sources

Functions

gboolean	(*GstControlSourceGetValue) ()
gboolean	(*GstControlSourceGetValueArray) ()
gboolean	gst_control_source_get_value ()
gboolean	gst_control_source_get_value_array ()

Types and Values

	GstValueArray
struct	GstControlSource
struct	GstControlSourceClass
struct	GstTimedValue

Object Hierarchy

    GObject
    ╰── GInitiallyUnowned
        ╰── GstObject
            ╰── GstControlSource

Includes

#include <gst/gst.h>

Description

The GstControlSource is a base class for control value sources that could be used to get timestamp-value pairs. A control source essentially is a function over time, returning float values between 0.0 and 1.0.

A GstControlSource is used by first getting an instance of a specific control-source, creating a binding for the control-source to the target property of the element and then adding the binding to the element. The binding will convert the data types and value range to fit to the bound property.

For implementing a new GstControlSource one has to implement GstControlSourceGetValue and GstControlSourceGetValueArray functions. These are then used by gst_control_source_get_value() and gst_control_source_get_value_array() to get values for specific timestamps.

Functions

GstControlSourceGetValue ()

gboolean
(*GstControlSourceGetValue) (GstControlSource *self,
                             GstClockTime timestamp,
                             gdouble *value);

Function for returning a value for a given timestamp.

Parameters

self	the GstControlSource instance
timestamp	timestamp for which a value should be calculated
value	a value which will be set to the result.

Returns

TRUE if the value was successfully calculated.

GstControlSourceGetValueArray ()

gboolean
(*GstControlSourceGetValueArray) (GstControlSource *self,
                                  GstClockTime timestamp,
                                  GstClockTime interval,
                                  guint n_values,
                                  gdouble *values);

Function for returning an array of values for starting at a given timestamp.

Parameters

self	the GstControlSource instance
timestamp	timestamp for which a value should be calculated
interval	the time spacing between subsequent values
n_values	the number of values
values	array to put control-values in

Returns

TRUE if the values were successfully calculated.

gst_control_source_get_value ()

gboolean
gst_control_source_get_value (GstControlSource *self,
                              GstClockTime timestamp,
                              gdouble *value);

Gets the value for this GstControlSource at a given timestamp.

[method]

Parameters

self	the GstControlSource object
timestamp	the time for which the value should be returned
value	the value.	[out]

Returns

FALSE if the value couldn't be returned, TRUE otherwise.

gst_control_source_get_value_array ()

gboolean
gst_control_source_get_value_array (GstControlSource *self,
                                    GstClockTime timestamp,
                                    GstClockTime interval,
                                    guint n_values,
                                    gdouble *values);

Gets an array of values for for this GstControlSource. Values that are undefined contain NANs.

[method]

Parameters

self	the GstControlSource object
timestamp	the first timestamp
interval	the time steps
n_values	the number of values to fetch
values	array to put control-values in.	[array length=n_values]

Returns

TRUE if the given array could be filled, FALSE otherwise

Types and Values

GstValueArray

typedef struct _GstValueArray GstValueArray;

struct GstControlSource

struct GstControlSource {
  GstControlSourceGetValue get_value;             /* Returns the value for a property at a given timestamp */
  GstControlSourceGetValueArray get_value_array;  /* Returns values for a property in a given timespan */
};

The instance structure of GstControlSource.

Members

GstControlSourceGetValue `get_value`;	Function for returning a value for a given timestamp
GstControlSourceGetValueArray `get_value_array`;	Function for returning a values array for a given timestamp

struct GstControlSourceClass

struct GstControlSourceClass {
  GstObjectClass parent_class;
};

The class structure of GstControlSource.

Members

struct GstTimedValue

struct GstTimedValue {
  GstClockTime timestamp;
  gdouble      value;
};

Structure for saving a timestamp and a value.

Members

GstClockTime `timestamp`;	timestamp of the value change
gdouble `value`;	the corresponding value