GstClock

## GstClock GstClock — Abstract class for global clocks |

## Synopsis

    #include <gst/gst.h>

                        GstClock;
                        GstClockClass;
    typedef             GstClockTime;
    typedef             GstClockTimeDiff;
    typedef             GstClockID;
    #define             GST_CLOCK_TIME_NONE
    #define             GST_CLOCK_TIME_IS_VALID             (time)
    #define             GST_SECOND
    #define             GST_MSECOND
    #define             GST_USECOND
    #define             GST_NSECOND
    #define             GST_TIME_AS_SECONDS                 (time)
    #define             GST_TIME_AS_MSECONDS                (time)
    #define             GST_TIME_AS_USECONDS                (time)
    #define             GST_TIME_AS_NSECONDS                (time)
    #define             GST_CLOCK_DIFF                      (s, e)
    #define             GST_TIMEVAL_TO_TIME                 (tv)
    #define             GST_TIME_TO_TIMEVAL                 (t,tv)
    #define             GST_TIMESPEC_TO_TIME                (ts)
    #define             GST_TIME_TO_TIMESPEC                (t,ts)
    #define             GST_CLOCK_ENTRY_TRACE_NAME
                        GstClockEntry;
    gboolean            (*GstClockCallback)                 (GstClock *clock,
                                                             GstClockTime time,
                                                             GstClockID id,
                                                             gpointer user_data);
    enum                GstClockEntryType;
    #define             GST_CLOCK_ENTRY                     (entry)
    #define             GST_CLOCK_ENTRY_CLOCK               (entry)
    #define             GST_CLOCK_ENTRY_TYPE                (entry)
    #define             GST_CLOCK_ENTRY_TIME                (entry)
    #define             GST_CLOCK_ENTRY_INTERVAL            (entry)
    #define             GST_CLOCK_ENTRY_STATUS              (entry)
    enum                GstClockReturn;
    enum                GstClockFlags;
    #define             GST_CLOCK_FLAGS                     (clock)
    #define             GST_CLOCK_BROADCAST                 (clock)
    #define             GST_CLOCK_COND                      (clock)
    #define             GST_CLOCK_TIMED_WAIT                (clock,tv)
    #define             GST_CLOCK_WAIT                      (clock)
    gboolean            gst_clock_add_observation           (GstClock *clock,
                                                             GstClockTime slave,
                                                             GstClockTime master,
                                                             gdouble *r_squared);
    gboolean            gst_clock_set_master                (GstClock *clock,
                                                             GstClock *master);
    GstClock*           gst_clock_get_master                (GstClock *clock);
    GstClockTime        gst_clock_set_resolution            (GstClock *clock,
                                                             GstClockTime resolution);
    GstClockTime        gst_clock_get_resolution            (GstClock *clock);
    GstClockTime        gst_clock_get_time                  (GstClock *clock);
    GstClockID          gst_clock_new_single_shot_id        (GstClock *clock,
                                                             GstClockTime time);
    GstClockID          gst_clock_new_periodic_id           (GstClock *clock,
                                                             GstClockTime start_time,
                                                             GstClockTime interval);
    GstClockTime        gst_clock_get_internal_time         (GstClock *clock);
    GstClockTime        gst_clock_adjust_unlocked           (GstClock *clock,
                                                             GstClockTime internal);
    GstClockTime        gst_clock_unadjust_unlocked         (GstClock *clock,
                                                             GstClockTime external);
    void                gst_clock_get_calibration           (GstClock *clock,
                                                             GstClockTime *internal,
                                                             GstClockTime *external,
                                                             GstClockTime *rate_num,
                                                             GstClockTime *rate_denom);
    void                gst_clock_set_calibration           (GstClock *clock,
                                                             GstClockTime internal,
                                                             GstClockTime external,
                                                             GstClockTime rate_num,
                                                             GstClockTime rate_denom);
    GstClockTime        gst_clock_id_get_time               (GstClockID id);
    GstClockReturn      gst_clock_id_wait                   (GstClockID id,
                                                             GstClockTimeDiff *jitter);
    GstClockReturn      gst_clock_id_wait_async             (GstClockID id,
                                                             GstClockCallback func,
                                                             gpointer user_data);
    void                gst_clock_id_unschedule             (GstClockID id);
    gint                gst_clock_id_compare_func           (gconstpointer id1,
                                                             gconstpointer id2);
    GstClockID          gst_clock_id_ref                    (GstClockID id);
    void                gst_clock_id_unref                  (GstClockID id);

## Object Hierarchy

      GObject
       +----GstObject
             +----GstClock
                   +----GstSystemClock

## Properties

      "stats"                    gboolean              : Read / Write
      "timeout"                  guint64               : Read / Write
      "window-size"              gint                  : Read / Write
      "window-threshold"         gint                  : Read / Write

## Description

GStreamer uses a global clock to synchronize the plugins in a pipeline. Different clock implementations are possible by implementing this abstract base class.

The GstClock returns a monotonically increasing time with the method `gst_clock_get_time()`. Its accuracy and base time depend on the specific clock implementation but time is always expressed in nanoseconds. Since the baseline of the clock is undefined, the clock time returned is not meaningful in itself, what matters are the deltas between two clock times. The time returned by a clock is called the absolute time.

The pipeline uses the clock to calculate the stream time. Usually all renderers synchronize to the global clock using the buffer timestamps, the newsegment events and the element's base time, see GstPipeline.

A clock implementation can support periodic and single shot clock notifications both synchronous and asynchronous.

One first needs to create a GstClockID for the periodic or single shot notification using `gst_clock_new_single_shot_id()` or `gst_clock_new_periodic_id()`.

To perform a blocking wait for the specific time of the GstClockID use the `gst_clock_id_wait()`. To receive a callback when the specific time is reached in the clock use `gst_clock_id_wait_async()`. Both these calls can be interrupted with the `gst_clock_id_unschedule()` call. If the blocking wait is unscheduled a return value of GST_CLOCK_UNSCHEDULED is returned.

Periodic callbacks scheduled async will be repeatedly called automatically until it is unscheduled. To schedule a sync periodic callback, `gst_clock_id_wait()` should be called repeatedly.

The async callbacks can happen from any thread, either provided by the core or from a streaming thread. The application should be prepared for this.

A GstClockID that has been unscheduled cannot be used again for any wait operation, a new GstClockID should be created and the old unscheduled one should be destroyed with `gst_clock_id_unref()`.

It is possible to perform a blocking wait on the same GstClockID from multiple threads. However, registering the same GstClockID for multiple async notifications is not possible, the callback will only be called for the thread registering the entry last.

None of the wait operations unref the GstClockID, the owner is responsible for unreffing the ids itself. This holds for both periodic and single shot notifications. The reason being that the owner of the GstClockID has to keep a handle to the GstClockID to unblock the wait on FLUSHING events or state changes and if the entry would be unreffed automatically, the handle might become invalid without any notification.

These clock operations do not operate on the stream time, so the callbacks will also occur when not in PLAYING state as if the clock just keeps on running. Some clocks however do not progress when the element that provided the clock is not PLAYING.

When a clock has the GST_CLOCK_FLAG_CAN_SET_MASTER flag set, it can be slaved to another GstClock with the `gst_clock_set_master()`. The clock will then automatically be synchronized to this master clock by repeatedly sampling the master clock and the slave clock and recalibrating the slave clock with `gst_clock_set_calibration()`. This feature is mostly useful for plugins that have an internal clock but must operate with another clock selected by the GstPipeline. They can track the offset and rate difference of their internal clock relative to the master clock by using the `gst_clock_get_calibration()` function.

The master/slave synchronisation can be tuned with the "timeout", "window-size" and "window-threshold" properties. The "timeout" property defines the interval to sample the master clock and run the calibration functions. "window-size" defines the number of samples to use when calibrating and "window-threshold" defines the minimum number of samples before the calibration is performed.

Last reviewed on 2006-08-11 (0.10.10)

## Details

### GstClock

    typedef struct _GstClock GstClock;

### GstClockClass

    typedef struct {
      GstObjectClass        parent_class;

      /* vtable */
      GstClockTime          (*change_resolution)    (GstClock *clock,
                                                     GstClockTime old_resolution,
    						 GstClockTime new_resolution);
      GstClockTime          (*get_resolution)       (GstClock *clock);

      GstClockTime		(*get_internal_time)	(GstClock *clock);

      /* waiting on an ID */
      GstClockReturn        (*wait)			(GstClock *clock, GstClockEntry *entry);
      GstClockReturn        (*wait_async)           (GstClock *clock, GstClockEntry *entry);
      void                  (*unschedule)		(GstClock *clock, GstClockEntry *entry);

      /* ABI added to replace the deprecated wait */
      GstClockReturn        (*wait_jitter)		(GstClock *clock, GstClockEntry *entry,
    		  				 GstClockTimeDiff *jitter);
    } GstClockClass;

GStreamer clock class. Override the vmethods to implement the clock functionality.

GstObjectClass `parent_class`; | the parent class structure
`change_resolution` () | change the resolution of the clock. Not all values might be acceptable. The new resolution should be returned.
`get_resolution` () | get the resolution of the clock.
`get_internal_time` () | get the internal unadjusted time of the clock.
`wait` () | perform a blocking wait for the given GstClockEntry. Deprecated, implement `wait_jitter` instead.
`wait_async` () | perform an asynchronous wait for the given GstClockEntry.
`unschedule` () | unblock a blocking or async wait operation.
`wait_jitter` () | perform a blocking wait on the given GstClockEntry and return the jitter. (Since: 0.10.10)

### GstClockTime

    typedef guint64	GstClockTime;

A datatype to hold a time, measured in nanoseconds.

### GstClockTimeDiff

    typedef gint64 GstClockTimeDiff;

A datatype to hold a time difference, measured in nanoseconds.

### GstClockID

    typedef gpointer GstClockID;

A datatype to hold the handle to an outstanding sync or async clock callback.

### GST_CLOCK_TIME_NONE

    #define GST_CLOCK_TIME_NONE		((GstClockTime) -1)

Constant to define an undefined clock time.

### GST_CLOCK_TIME_IS_VALID()

    #define GST_CLOCK_TIME_IS_VALID(time)	(((GstClockTime)(time)) != GST_CLOCK_TIME_NONE)

Tests if a given GstClockTime represents a valid defined time.

`time` : | clock time to validate

### GST_SECOND

    #define GST_SECOND  (G_USEC_PER_SEC * G_GINT64_CONSTANT (1000))

Constant that defines one GStreamer second.

### GST_MSECOND

    #define GST_MSECOND (GST_SECOND / G_GINT64_CONSTANT (1000))

Constant that defines one GStreamer millisecond.

### GST_USECOND

    #define GST_USECOND (GST_SECOND / G_GINT64_CONSTANT (1000000))

Constant that defines one GStreamer microsecond.

### GST_NSECOND

    #define GST_NSECOND (GST_SECOND / G_GINT64_CONSTANT (1000000000))

Constant that defines one GStreamer nanosecond

### GST_TIME_AS_SECONDS()

    #define GST_TIME_AS_SECONDS(time)  ((time) / GST_SECOND)

Convert a GstClockTime to seconds.

`time` : | the time

Since 0.10.16

### GST_TIME_AS_MSECONDS()

    #define GST_TIME_AS_MSECONDS(time) ((time) / G_GINT64_CONSTANT (1000000))

Convert a GstClockTime to milliseconds (1/1000 of a second).

`time` : | the time

Since 0.10.16

### GST_TIME_AS_USECONDS()

    #define GST_TIME_AS_USECONDS(time) ((time) / G_GINT64_CONSTANT (1000))

Convert a GstClockTime to microseconds (1/1000000 of a second).

`time` : | the time

Since 0.10.16

### GST_TIME_AS_NSECONDS()

    #define GST_TIME_AS_NSECONDS(time) (time)

Convert a GstClockTime to nanoseconds (1/1000000000 of a second).

`time` : | the time

Since 0.10.16

### GST_CLOCK_DIFF()

    #define GST_CLOCK_DIFF(s, e)		(GstClockTimeDiff)((e) - (s))

Calculate a difference between two clock times as a GstClockTimeDiff. The difference is calculated as `e` - `s`.

`s` : | the first time
`e` : | the second time

### GST_TIMEVAL_TO_TIME()

    #define GST_TIMEVAL_TO_TIME(tv)		(GstClockTime)((tv).tv_sec * GST_SECOND + (tv).tv_usec * GST_USECOND)

Convert a GTimeVal to a GstClockTime.

`tv` : | the timeval to convert

### GST_TIME_TO_TIMEVAL()

    #define             GST_TIME_TO_TIMEVAL(t,tv)

Note: on 32-bit systems, a timeval has a range of only 2^32 - 1 seconds, which is about 68 years. Expect trouble if you want to schedule stuff in your pipeline for 2038.

Convert a GstClockTime to a GTimeVal

`t` : | The GstClockTime to convert
`tv` : | The target timeval

### GST_TIMESPEC_TO_TIME()

    #define GST_TIMESPEC_TO_TIME(ts)	(GstClockTime)((ts).tv_sec * GST_SECOND + (ts).tv_nsec * GST_NSECOND)

Convert a struct timespec (see man pselect) to a GstClockTime.

`ts` : | the timespec to convert

### GST_TIME_TO_TIMESPEC()

    #define             GST_TIME_TO_TIMESPEC(t,ts)

Convert a GstClockTime to a struct timespec (see man pselect)

`t` : | The GstClockTime to convert
`ts` : | The target timespec

### GST_CLOCK_ENTRY_TRACE_NAME

    #define GST_CLOCK_ENTRY_TRACE_NAME "GstClockEntry"

The name used for tracing clock entry allocations.

### GstClockEntry

    typedef struct {
      gint			refcount;
    } GstClockEntry;

All pending timeouts or periodic notifies are converted into an entry.

gint `refcount`; | reference counter (read-only)

### GstClockCallback ()

    gboolean            (*GstClockCallback)                 (GstClock *clock,
                                                             GstClockTime time,
                                                             GstClockID id,
                                                             gpointer user_data);

The function prototype of the callback.

`clock` : | The clock that triggered the callback
`time` : | The time it was triggered
`id` : | The GstClockID that expired
`user_data` : | user data passed in the `gst_clock_id_wait_async()` function
Returns : | `TRUE` or `FALSE` (currently unused)

### enum GstClockEntryType

    typedef enum {
      GST_CLOCK_ENTRY_SINGLE,
      GST_CLOCK_ENTRY_PERIODIC
    } GstClockEntryType;

The type of the clock entry

`GST_CLOCK_ENTRY_SINGLE` | a single shot timeout
`GST_CLOCK_ENTRY_PERIODIC` | a periodic timeout request

### GST_CLOCK_ENTRY()

    #define GST_CLOCK_ENTRY(entry)		((GstClockEntry *)(entry))

Cast to a clock entry

`entry` : | the entry to cast

### GST_CLOCK_ENTRY_CLOCK()

    #define GST_CLOCK_ENTRY_CLOCK(entry)	((entry)->clock)

Get the owner clock of the entry

`entry` : | the entry to query

### GST_CLOCK_ENTRY_TYPE()

    #define GST_CLOCK_ENTRY_TYPE(entry)	((entry)->type)

Get the type of the clock entry

`entry` : | the entry to query

### GST_CLOCK_ENTRY_TIME()

    #define GST_CLOCK_ENTRY_TIME(entry)	((entry)->time)

Get the requested time of this entry

`entry` : | the entry to query

### GST_CLOCK_ENTRY_INTERVAL()

    #define GST_CLOCK_ENTRY_INTERVAL(entry)	((entry)->interval)

Get the interval of this periodic entry

`entry` : | the entry to query

### GST_CLOCK_ENTRY_STATUS()

    #define GST_CLOCK_ENTRY_STATUS(entry)	((entry)->status)

The status of the entry

`entry` : | the entry to query

### enum GstClockReturn

    typedef enum
    {
      GST_CLOCK_OK		=  0,
      GST_CLOCK_EARLY	=  1,
      GST_CLOCK_UNSCHEDULED	=  2,
      GST_CLOCK_BUSY	=  3,
      GST_CLOCK_BADTIME	=  4,
      GST_CLOCK_ERROR	=  5,
      GST_CLOCK_UNSUPPORTED	=  6
    } GstClockReturn;

The return value of a clock operation.

`GST_CLOCK_OK` | The operation succeeded.
`GST_CLOCK_EARLY` | The operation was scheduled too late.
`GST_CLOCK_UNSCHEDULED` | The clockID was unscheduled
`GST_CLOCK_BUSY` | The ClockID is busy
`GST_CLOCK_BADTIME` | A bad time was provided to a function.
`GST_CLOCK_ERROR` | An error occurred
`GST_CLOCK_UNSUPPORTED` | Operation is not supported

### enum GstClockFlags

    typedef enum {
      GST_CLOCK_FLAG_CAN_DO_SINGLE_SYNC     = (GST_OBJECT_FLAG_LAST << 0),
      GST_CLOCK_FLAG_CAN_DO_SINGLE_ASYNC    = (GST_OBJECT_FLAG_LAST << 1),
      GST_CLOCK_FLAG_CAN_DO_PERIODIC_SYNC   = (GST_OBJECT_FLAG_LAST << 2),
      GST_CLOCK_FLAG_CAN_DO_PERIODIC_ASYNC  = (GST_OBJECT_FLAG_LAST << 3),
      GST_CLOCK_FLAG_CAN_SET_RESOLUTION     = (GST_OBJECT_FLAG_LAST << 4),
      GST_CLOCK_FLAG_CAN_SET_MASTER         = (GST_OBJECT_FLAG_LAST << 5),
      /* padding */
      GST_CLOCK_FLAG_LAST		        = (GST_OBJECT_FLAG_LAST << 8)
    } GstClockFlags;

The capabilities of this clock

`GST_CLOCK_FLAG_CAN_DO_SINGLE_SYNC` | clock can do a single sync timeout request
`GST_CLOCK_FLAG_CAN_DO_SINGLE_ASYNC` | clock can do a single async timeout request
`GST_CLOCK_FLAG_CAN_DO_PERIODIC_SYNC` | clock can do sync periodic timeout requests
`GST_CLOCK_FLAG_CAN_DO_PERIODIC_ASYNC` | clock can do async periodic timeout callbacks
`GST_CLOCK_FLAG_CAN_SET_RESOLUTION` | clock's resolution can be changed
`GST_CLOCK_FLAG_CAN_SET_MASTER` | clock can be slaved to a master clock
`GST_CLOCK_FLAG_LAST` | subclasses can add additional flags starting from this flag

### GST_CLOCK_FLAGS()

    #define GST_CLOCK_FLAGS(clock)  GST_OBJECT_FLAGS(clock)

Gets the GstClockFlags clock flags.

`clock` : | the clock to query

### GST_CLOCK_BROADCAST()

    #define GST_CLOCK_BROADCAST(clock)       g_cond_broadcast(GST_CLOCK_COND(clock))

Signal that the entries in the clock have changed.

`clock` : | the clock to broadcast

### GST_CLOCK_COND()

    #define GST_CLOCK_COND(clock)            (GST_CLOCK_CAST(clock)->entries_changed)

Gets the GCond that gets signalled when the entries of the clock changed.

`clock` : | the clock to query

### GST_CLOCK_TIMED_WAIT()

    #define GST_CLOCK_TIMED_WAIT(clock,tv)   g_cond_timed_wait(GST_CLOCK_COND(clock),GST_OBJECT_GET_LOCK(clock),tv)

Wait on the clock until the entries changed or the specified timeout occurred.

`clock` : | the clock to wait on
`tv` : | a GTimeVal to wait.

### GST_CLOCK_WAIT()

    #define GST_CLOCK_WAIT(clock)            g_cond_wait(GST_CLOCK_COND(clock),GST_OBJECT_GET_LOCK(clock))

Wait on the clock until the entries changed.

`clock` : | the clock to wait on

### gst_clock_add_observation ()

    gboolean            gst_clock_add_observation           (GstClock *clock,
                                                             GstClockTime slave,
                                                             GstClockTime master,
                                                             gdouble *r_squared);

The time `master` of the master clock and the time `slave` of the slave clock are added to the list of observations. If enough observations are available, a linear regression algorithm is run on the observations and `clock` is recalibrated.

If this functions returns `TRUE`, `r_squared` will contain the correlation coefficient of the interpolation. A value of 1.0 means a perfect regression was performed. This value can be used to control the sampling frequency of the master and slave clocks.

`clock` : | a GstClock
`slave` : | a time on the slave
`master` : | a time on the master
`r_squared` : | a pointer to hold the result
Returns : | `TRUE` if enough observations were added to run the regression algorithm. MT safe.

### gst_clock_set_master ()

    gboolean            gst_clock_set_master                (GstClock *clock,
                                                             GstClock *master);

Set `master` as the master clock for `clock`. `clock` will be automatically calibrated so that `gst_clock_get_time()` reports the same time as the master clock.

A clock provider that slaves its clock to a master can get the current calibration values with `gst_clock_get_calibration()`.

`master` can be `NULL` in which case `clock` will not be slaved anymore. It will however keep reporting its time adjusted with the last configured rate and time offsets.

`clock` : | a GstClock
`master` : | a master GstClock
Returns : | `TRUE` if the clock is capable of being slaved to a master clock. Trying to set a master on a clock without the GST_CLOCK_FLAG_CAN_SET_MASTER flag will make this function return `FALSE`. MT safe.

### gst_clock_get_master ()

    GstClock*           gst_clock_get_master                (GstClock *clock);

Get the master clock that `clock` is slaved to or `NULL` when the clock is not slaved to any master clock.

`clock` : | a GstClock
Returns : | a master GstClock or `NULL` when this clock is not slaved to a master clock. Unref after usage. MT safe.

### gst_clock_set_resolution ()

    GstClockTime        gst_clock_set_resolution            (GstClock *clock,
                                                             GstClockTime resolution);

Set the accuracy of the clock. Some clocks have the possibility to operate with different accuracy at the expense of more resource usage. There is normally no need to change the default resolution of a clock. The resolution of a clock can only be changed if the clock has the GST_CLOCK_FLAG_CAN_SET_RESOLUTION flag set.

`clock` : | a GstClock
`resolution` : | The resolution to set
Returns : | the new resolution of the clock.

### gst_clock_get_resolution ()

    GstClockTime        gst_clock_get_resolution            (GstClock *clock);

Get the accuracy of the clock. The accuracy of the clock is the granularity of the values returned by `gst_clock_get_time()`.

`clock` : | a GstClock
Returns : | the resolution of the clock in units of GstClockTime. MT safe.

### gst_clock_get_time ()

    GstClockTime        gst_clock_get_time                  (GstClock *clock);

Gets the current time of the given clock. The time is always monotonically increasing and adjusted according to the current offset and rate.

`clock` : | a GstClock to query
Returns : | the time of the clock. Or GST_CLOCK_TIME_NONE when given invalid input. MT safe.

### gst_clock_new_single_shot_id ()

    GstClockID          gst_clock_new_single_shot_id        (GstClock *clock,
                                                             GstClockTime time);

Get a GstClockID from `clock` to trigger a single shot notification at the requested time. The single shot id should be unreffed after usage.

`clock` : | The GstClockID to get a single shot notification from
`time` : | the requested time
Returns : | A GstClockID that can be used to request the time notification. MT safe.

### gst_clock_new_periodic_id ()

    GstClockID          gst_clock_new_periodic_id           (GstClock *clock,
                                                             GstClockTime start_time,
                                                             GstClockTime interval);

Get an ID from `clock` to trigger a periodic notification. The periodic notifications will start at time `start_time` and will then be fired with the given `interval`. `id` should be unreffed after usage.

`clock` : | The GstClockID to get a periodic notification id from
`start_time` : | the requested start time
`interval` : | the requested interval
Returns : | A GstClockID that can be used to request the time notification. MT safe.

### gst_clock_get_internal_time ()

    GstClockTime        gst_clock_get_internal_time         (GstClock *clock);

Gets the current internal time of the given clock. The time is returned unadjusted for the offset and the rate.

`clock` : | a GstClock to query
Returns : | the internal time of the clock. Or GST_CLOCK_TIME_NONE when given invalid input. MT safe.

### gst_clock_adjust_unlocked ()

    GstClockTime        gst_clock_adjust_unlocked           (GstClock *clock,
                                                             GstClockTime internal);

Converts the given `internal` clock time to the external time, adjusting for the rate and reference time set with `gst_clock_set_calibration()` and making sure that the returned time is increasing. This function should be called with the clock's OBJECT_LOCK held and is mainly used by clock subclasses.

This function is the reverse of `gst_clock_unadjust_unlocked()`.

`clock` : | a GstClock to use
`internal` : | a clock time
Returns : | the converted time of the clock.

### gst_clock_unadjust_unlocked ()

    GstClockTime        gst_clock_unadjust_unlocked         (GstClock *clock,
                                                             GstClockTime external);

Converts the given `external` clock time to the internal time of `clock`, using the rate and reference time set with `gst_clock_set_calibration()`. This function should be called with the clock's OBJECT_LOCK held and is mainly used by clock subclasses.

This function is the reverse of `gst_clock_adjust_unlocked()`.

`clock` : | a GstClock to use
`external` : | an external clock time
Returns : | the internal time of the clock corresponding to `external`.

Since 0.10.13

### gst_clock_get_calibration ()

    void                gst_clock_get_calibration           (GstClock *clock,
                                                             GstClockTime *internal,
                                                             GstClockTime *external,
                                                             GstClockTime *rate_num,
                                                             GstClockTime *rate_denom);

Gets the internal rate and reference time of `clock`. See `gst_clock_set_calibration()` for more information.

`internal`, `external`, `rate_num`, and `rate_denom` can be left `NULL` if the caller is not interested in the values.

MT safe.

`clock` : | a GstClock
`internal` : | a location to store the internal time
`external` : | a location to store the external time
`rate_num` : | a location to store the rate numerator
`rate_denom` : | a location to store the rate denominator

### gst_clock_set_calibration ()

    void                gst_clock_set_calibration           (GstClock *clock,
                                                             GstClockTime internal,
                                                             GstClockTime external,
                                                             GstClockTime rate_num,
                                                             GstClockTime rate_denom);

Adjusts the rate and time of `clock`. A rate of 1/1 is the normal speed of the clock. Values bigger than 1/1 make the clock go faster.

`internal` and `external` are calibration parameters that arrange that `gst_clock_get_time()` should have been `external` at internal time `internal`. This internal time should not be in the future; that is, it should be less than the value of `gst_clock_get_internal_time()` when this function is called.

Subsequent calls to `gst_clock_get_time()` will return clock times computed as follows:

      time = (internal_time - internal) * rate_num / rate_denom + external

This formula is implemented in `gst_clock_adjust_unlocked()`. Of course, it tries to do the integer arithmetic as precisely as possible.

Note that `gst_clock_get_time()` always returns increasing values so when you move the clock backwards, `gst_clock_get_time()` will report the previous value until the clock catches up.

MT safe.

`clock` : | a GstClock to calibrate
`internal` : | a reference internal time
`external` : | a reference external time
`rate_num` : | the numerator of the rate of the clock relative to its internal time
`rate_denom` : | the denominator of the rate of the clock

### gst_clock_id_get_time ()

    GstClockTime        gst_clock_id_get_time               (GstClockID id);

Get the time of the clock ID

`id` : | The GstClockID to query
Returns : | the time of the given clock id. MT safe.

### gst_clock_id_wait ()

    GstClockReturn      gst_clock_id_wait                   (GstClockID id,
                                                             GstClockTimeDiff *jitter);

Perform a blocking wait on `id`. `id` should have been created with `gst_clock_new_single_shot_id()` or `gst_clock_new_periodic_id()` and should not have been unscheduled with a call to `gst_clock_id_unschedule()`.

If the `jitter` argument is not `NULL` and this function returns GST_CLOCK_OK or GST_CLOCK_EARLY, it will contain the difference against the clock and the time of `id` when this method was called. Positive values indicate how late `id` was relative to the clock (in which case this function will return GST_CLOCK_EARLY). Negative values indicate how much time was spent waiting on the clock before this function returned.

`id` : | The GstClockID to wait on
`jitter` : | A pointer that will contain the jitter, can be `NULL`.
Returns : | the result of the blocking wait. GST_CLOCK_EARLY will be returned if the current clock time is past the time of `id`, GST_CLOCK_OK if `id` was scheduled in time. GST_CLOCK_UNSCHEDULED if `id` was unscheduled with `gst_clock_id_unschedule()`. MT safe.

### gst_clock_id_wait_async ()

    GstClockReturn      gst_clock_id_wait_async             (GstClockID id,
                                                             GstClockCallback func,
                                                             gpointer user_data);

Register a callback on the given GstClockID `id` with the given function and user_data. When passing a GstClockID with an invalid time to this function, the callback will be called immediately with a time set to GST_CLOCK_TIME_NONE. The callback will be called when the time of `id` has been reached.

`id` : | a GstClockID to wait on
`func` : | The callback function
`user_data` : | User data passed in the callback
Returns : | the result of the non blocking wait. MT safe.

### gst_clock_id_unschedule ()

    void                gst_clock_id_unschedule             (GstClockID id);

Cancel an outstanding request with `id`. This can either be an outstanding async notification or a pending sync notification. After this call, `id` cannot be used anymore to receive sync or async notifications, you need to create a new GstClockID.

MT safe.

`id` : | The id to unschedule

### gst_clock_id_compare_func ()

    gint                gst_clock_id_compare_func           (gconstpointer id1,
                                                             gconstpointer id2);

Compares the two GstClockID instances. This function can be used as a GCompareFunc when sorting ids.

`id1` : | A GstClockID
`id2` : | A GstClockID to compare with
Returns : | negative value if a < b; zero if a = b; positive value if a > b MT safe.

### gst_clock_id_ref ()

    GstClockID          gst_clock_id_ref                    (GstClockID id);

Increase the refcount of given `id`.

`id` : | The GstClockID to ref
Returns : | The same GstClockID with increased refcount. MT safe.

### gst_clock_id_unref ()

    void                gst_clock_id_unref                  (GstClockID id);

Unref given `id`. When the refcount reaches 0 the GstClockID will be freed.

MT safe.

`id` : | The GstClockID to unref

## Property Details

### The `"stats"` property

      "stats"                    gboolean              : Read / Write

Enable clock stats (unimplemented).

Default value: FALSE

### The `"timeout"` property

      "timeout"                  guint64               : Read / Write

The amount of time, in nanoseconds, to sample master and slave clocks.

Default value: 100000000

### The `"window-size"` property

      "window-size"              gint                  : Read / Write

The size of the window used to calculate rate and offset.

Allowed values: [2,1024]

Default value: 32

### The `"window-threshold"` property

      "window-threshold"         gint                  : Read / Write

The threshold to start calculating rate and offset.

Allowed values: [2,1024]

Default value: 4

## See Also

GstSystemClock, GstPipeline