GstClock

GstClock — Abstract class for global clocks

Synopsis


#include <gst/gst.h>


            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_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);
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);
#define     GST_TYPE_CLOCK_TIME


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 depends on the specific clock implementation but time is always expessed 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 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.

The time of the clock in itself is not very useful for an application.

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 repeadedly called automatically until it is unscheduled. To schedule an async periodic callback, gst_clock_id_wait() should be called repeadedly.

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.

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 once.

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 we unref it automatically, the handle might be invalid.

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 repeadedly sampling the master clock and the slave clock and recalibrating the slave clock with gst_clock_set_calibration(). This feature is mostly usefull 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.

Last reviewed on 2005-10-28 (0.9.4)

Details

GstClock

typedef struct _GstClock GstClock;

GstClock base structure. The values of this structure are protected for subclasses, use the methods to use the 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 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)	((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_CLOCK_DIFF()

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

Calculate a difference between two clock times as a GstClockTimeDiff.

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)

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)		((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 async_wait call
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 succeded.
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 occured
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_CLOCK(clock)->flags)

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 signaled 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 occured.

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.

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().

clock : a GstClock
master : a master GstClock
Returns : TRUE if the clock is capable of being slaved to a master clock. 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.

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.

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 giving wrong input. MT safe.

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. The single shot id should be unreffed after usage.

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. MT safe.

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. The id should be unreffed after usage.

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. 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 giving wrong input. MT safe.

gst_clock_adjust_unlocked ()

GstClockTime gst_clock_adjust_unlocked      (GstClock *clock,
                                             GstClockTime internal);

Converts the given internal clock time to the real 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.

clock : a GstClock to use
internal : a clock time
Returns : the converted time of the clock. MT safe.

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

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. MT safe.

gst_clock_id_unschedule ()

void        gst_clock_id_unschedule         (GstClockID id);

Cancel an outstanding request with the given ID. This can either be an outstanding async notification or a pending sync notification. After this call, the 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 clockid
id2 : A clockid 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 the given clockid.

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

gst_clock_id_unref ()

void        gst_clock_id_unref              (GstClockID id);

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

MT safe.

id : The clockid to unref

GST_TYPE_CLOCK_TIME

#define GST_TYPE_CLOCK_TIME G_TYPE_UINT64

The GType of a GstClockTime.

Properties

The "stats" property

  "stats"                gboolean              : Read / Write

Enable clock stats.

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