## GstClock

GstClock — Abstract class for global clocks

## Synopsis

    struct      GstClock;
    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_CLOCK_DIFF                  (s, e)
    #define     GST_TIMEVAL_TO_TIME             (tv)
    #define     GST_TIME_TO_TIMEVAL             (t,tv)
    #define     GST_CLOCK_ENTRY_TRACE_NAME
    struct      GstClockEntry;
    gboolean    (*GstClockCallback)             (GstClock *clock,
                                                 GstClockTime time,
                                                 GstClockID id,
                                                 gpointer user_data);
    enum        GstClockEntryStatus;
    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)
    gdouble     gst_clock_set_speed             (GstClock *clock,
                                                 gdouble speed);
    gdouble     gst_clock_get_speed             (GstClock *clock);
    guint64     gst_clock_set_resolution        (GstClock *clock,
                                                 guint64 resolution);
    guint64     gst_clock_get_resolution        (GstClock *clock);
    void        gst_clock_set_active            (GstClock *clock,
                                                 gboolean active);
    gboolean    gst_clock_is_active             (GstClock *clock);
    void        gst_clock_reset                 (GstClock *clock);
    gboolean    gst_clock_handle_discont        (GstClock *clock,
                                                 guint64 time);
    GstClockTime gst_clock_get_time             (GstClock *clock);
    GstClockTime gst_clock_get_event_time       (GstClock *clock);
    GstClockTime gst_clock_get_event_time_delay (GstClock *clock,
                                                 GstClockTime delay);
    GstClockID  gst_clock_get_next_id           (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_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);
    void        gst_clock_id_unlock             (GstClockID id);
    void        gst_clock_id_free               (GstClockID id);

## Object Hierarchy

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

## Properties

      "event-diff"           guint64              : Read / Write / Construct
      "max-diff"             gint64               : Read / Write
      "stats"                gboolean             : Read / Write

## Description

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

The clock time is always measured in nanoseconds, with the clock being set to 0 when the pipeline goes to READY. Usually all renderers sync to the global clock so that the clock is always a good measure of the time in the pipeline.

## Details

### struct GstClock

    struct GstClock;

### GstClockTime

    typedef guint64 	GstClockTime;

A datatype to hold a time, measured in nanoseconds.

### GstClockTimeDiff

    typedef gint64 		GstClockTimeDiff;

A datatype to hold a timedifference, measured in nanoseconds.

### GstClockID

    typedef gpointer 	GstClockID;

A detatype to hold the handle to an outstanding 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)	((time) != GST_CLOCK_TIME_NONE)

`time` : |

### 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_CLOCK_DIFF()

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

Calculate a difference between to clock times.

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

### GST_TIMEVAL_TO_TIME()

    #define GST_TIMEVAL_TO_TIME(tv)		((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)

Convert a GstClockTime to a GTimeVal

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

### GST_CLOCK_ENTRY_TRACE_NAME

    #define GST_CLOCK_ENTRY_TRACE_NAME "GstClockEntry"

The name used for tracing clock entry allocations.

### struct GstClockEntry

    struct GstClockEntry {

      /* --- protected --- */
      GstClock	 	*clock;
      GstClockEntryType 	 type;
      GstClockTime 		 time;
      GstClockTime 		 interval;
      GstClockEntryStatus 	 status;
      GstClockCallback 	 func;
      gpointer		 user_data;
    };

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

### 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 id that expired
`user_data` : | user data passed in the async_wait call
Returns : |

### enum GstClockEntryStatus

    typedef enum {
      /* --- protected --- */
      GST_CLOCK_ENTRY_OK,
      GST_CLOCK_ENTRY_EARLY,
      GST_CLOCK_ENTRY_RESTART
    } GstClockEntryStatus;

The status of a clock timeout.

`GST_CLOCK_ENTRY_OK` | timeout happened
`GST_CLOCK_ENTRY_EARLY` | request for timout that has been passed
`GST_CLOCK_ENTRY_RESTART` | need to restart the timeout request

### enum GstClockEntryType

    typedef enum {
      /* --- protected --- */
      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_STOPPED 	= 0,
      GST_CLOCK_TIMEOUT 	= 1,
      GST_CLOCK_EARLY 	= 2,
      GST_CLOCK_ERROR 	= 3,
      GST_CLOCK_UNSUPPORTED	= 4
    } GstClockReturn;

The return value of a clock operation.

`GST_CLOCK_STOPPED` | The clock is stopped.
`GST_CLOCK_TIMEOUT` | The operation timed out.
`GST_CLOCK_EARLY` | The operation was scheduled too late.
`GST_CLOCK_ERROR` | An error occured
`GST_CLOCK_UNSUPPORTED` | Operation is not supported

### enum GstClockFlags

    typedef enum
    {
      GST_CLOCK_FLAG_CAN_DO_SINGLE_SYNC     = (1 << 1),
      GST_CLOCK_FLAG_CAN_DO_SINGLE_ASYNC    = (1 << 2),
      GST_CLOCK_FLAG_CAN_DO_PERIODIC_SYNC   = (1 << 3),
      GST_CLOCK_FLAG_CAN_DO_PERIODIC_ASYNC  = (1 << 4),
      GST_CLOCK_FLAG_CAN_SET_RESOLUTION     = (1 << 5),
      GST_CLOCK_FLAG_CAN_SET_SPEED          = (1 << 6)
    } GstClockFlags;

The capabilities of this clock

`GST_CLOCK_FLAG_CAN_DO_SINGLE_SYNC` | This clock can do a single sync timeut request
`GST_CLOCK_FLAG_CAN_DO_SINGLE_ASYNC` | This clock can do a single async timeout request
`GST_CLOCK_FLAG_CAN_DO_PERIODIC_SYNC` | This clock can do sync periodic timeout requests
`GST_CLOCK_FLAG_CAN_DO_PERIODIC_ASYNC` | This clock can do async periodic timeout callbacks
`GST_CLOCK_FLAG_CAN_SET_RESOLUTION` | The resolution of this clock can be changed
`GST_CLOCK_FLAG_CAN_SET_SPEED` | The speed of this clock can be changed

### GST_CLOCK_FLAGS()

    #define GST_CLOCK_FLAGS(clock)  (GST_CLOCK(clock)->flags)

Get the clock flags

`clock` : | the clock to query

### gst_clock_set_speed ()

    gdouble     gst_clock_set_speed             (GstClock *clock,
                                                 gdouble speed);

Sets the speed on the given clock. 1.0 is the default speed.

`clock` : | a GstClock to modify
`speed` : | the speed to set on the clock
Returns : | the new speed of the clock.

### gst_clock_get_speed ()

    gdouble     gst_clock_get_speed             (GstClock *clock);

Gets the speed of the given clock.

`clock` : | a GstClock to query
Returns : | the speed of the clock.

### gst_clock_set_resolution ()

    guint64     gst_clock_set_resolution        (GstClock *clock,
                                                 guint64 resolution);

Set the accuracy of the clock.

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

### gst_clock_get_resolution ()

    guint64     gst_clock_get_resolution        (GstClock *clock);

Get the accuracy of the clock.

`clock` : | The clock get the resolution of
Returns : | the resolution of the clock in microseconds.

### gst_clock_set_active ()

    void        gst_clock_set_active            (GstClock *clock,
                                                 gboolean active);

Activates or deactivates the clock based on the active parameter. As soon as the clock is activated, the time will start ticking.

`clock` : | a GstClock to set state of
`active` : | flag indicating if the clock should be activated (TRUE) or deactivated

### gst_clock_is_active ()

    gboolean    gst_clock_is_active             (GstClock *clock);

Checks if the given clock is active.

`clock` : | a GstClock to query
Returns : | TRUE if the clock is active.

### gst_clock_reset ()

    void        gst_clock_reset                 (GstClock *clock);

Reset the clock to time 0.

`clock` : | a GstClock to reset

### gst_clock_handle_discont ()

    gboolean    gst_clock_handle_discont        (GstClock *clock,
                                                 guint64 time);

Notifies the clock of a discontinuity in time.

`clock` : | a GstClock to notify of the discontinuity
`time` : | The new time
Returns : | TRUE if the clock was updated. It is possible that the clock was not updated by this call because only the first discontinuitity in the pipeline is honoured.

### 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.

`clock` : | a GstClock to query
Returns : | the time of the clock.

### gst_clock_get_event_time ()

    GstClockTime gst_clock_get_event_time       (GstClock *clock);

Gets the "event time" of a given clock. An event on the clock happens whenever this function is called. This ensures that multiple events that happen shortly after each other are treated as if they happened at the same time. GStreamer uses to keep state changes of multiple elements in sync.

`clock` : | clock to query
Returns : | the time of the event

### gst_clock_get_event_time_delay ()

    GstClockTime gst_clock_get_event_time_delay (GstClock *clock,
                                                 GstClockTime delay);

Gets the "event time" of a given clock. An event on the clock happens whenever this function is called. This ensures that multiple events that happen shortly after each other are treated as if they happened at the same time. GStreamer uses to keep state changes of multiple elements in sync.

When calling this function, the specified delay will be added to the current time to produce the event time. This can be used for events that are scheduled to happen at some point in the future.

`clock` : | clock to query
`delay` : | time before the event actually occurs
Returns : | the time of the event

### gst_clock_get_next_id ()

    GstClockID  gst_clock_get_next_id           (GstClock *clock);

Get the clockid of the next event.

`clock` : | The clock to query
Returns : | a clockid or NULL is no event is pending.

### gst_clock_new_single_shot_id ()

    GstClockID  gst_clock_new_single_shot_id    (GstClock *clock,
                                                 GstClockTime time);

Get an ID from the given clock to trigger a single shot notification at the requested time.

`clock` : | The clockid to get a single shot notification from
`time` : | the requested time
Returns : | An id that can be used to request the time notification.

### gst_clock_new_periodic_id ()

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

Get an ID from the given clock to trigger a periodic notification. The periodeic notifications will be start at time start_time and will then be fired with the given interval.

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

### gst_clock_id_get_time ()

    GstClockTime gst_clock_id_get_time          (GstClockID id);

Get the time of the clock ID

`id` : | The clockid to query
Returns : | the time of the given clock id

### gst_clock_id_wait ()

    GstClockReturn gst_clock_id_wait            (GstClockID id,
                                                 GstClockTimeDiff *jitter);

Perform a blocking wait on the given ID. The jitter arg can be NULL

`id` : | The clockid to wait on
`jitter` : | A pointer that will contain the jitter
Returns : | the result of the blocking wait.

### gst_clock_id_wait_async ()

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

Register a callback on the given clockid with the given function and user_data.

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

### gst_clock_id_unschedule ()

    void        gst_clock_id_unschedule         (GstClockID id);

Cancel an outstanding async notification request with the given ID.

`id` : | The id to unschedule

### gst_clock_id_unlock ()

    void        gst_clock_id_unlock             (GstClockID id);

Unlock the givan ClockID.

`id` : | The clockid to unlock

### gst_clock_id_free ()

    void        gst_clock_id_free               (GstClockID id);

Free the resources held by the given id

`id` : | The clockid to free

## Properties

"`event-diff`" (guint64 : Read / Write / Construct) | The amount of time that may elapse until 2 events are treated as happening at different times.
"`max-diff`" (gint64 : Read / Write) | Maximum allowed diff for clock sync requests against the real time.
"`stats`" (gboolean : Read / Write) | Boolean property to activate stat generation on the clock.

## See Also

GstSystemClock