appsink

appsink — Easy way for applications to extract samples from a pipeline

Synopsis

#include <gst/app/gstappsink.h>

void                gst_app_sink_set_caps               (GstAppSink *appsink,
                                                         const GstCaps *caps);
GstCaps *           gst_app_sink_get_caps               (GstAppSink *appsink);
gboolean            gst_app_sink_is_eos                 (GstAppSink *appsink);
void                gst_app_sink_set_emit_signals       (GstAppSink *appsink,
                                                         gboolean emit);
gboolean            gst_app_sink_get_emit_signals       (GstAppSink *appsink);
void                gst_app_sink_set_max_buffers        (GstAppSink *appsink,
                                                         guint max);
guint               gst_app_sink_get_max_buffers        (GstAppSink *appsink);
void                gst_app_sink_set_drop               (GstAppSink *appsink,
                                                         gboolean drop);
gboolean            gst_app_sink_get_drop               (GstAppSink *appsink);
GstSample *         gst_app_sink_pull_preroll           (GstAppSink *appsink);
GstSample *         gst_app_sink_pull_sample            (GstAppSink *appsink);
                    GstAppSinkCallbacks;
void                gst_app_sink_set_callbacks          (GstAppSink *appsink,
                                                         GstAppSinkCallbacks *callbacks,
                                                         gpointer user_data,
                                                         GDestroyNotify notify);

Description

Appsink is a sink plugin that supports many different methods for making the application get a handle on the GStreamer data in a pipeline. Unlike most GStreamer elements, Appsink provides external API functions.

appsink can be used by linking to the gstappsink.h header file to access the methods or by using the appsink action signals and properties.

The normal way of retrieving samples from appsink is by using the gst_app_sink_pull_sample() and gst_app_sink_pull_preroll() methods. These methods block until a sample becomes available in the sink or when the sink is shut down or reaches EOS.

Appsink will internally use a queue to collect buffers from the streaming thread. If the application is not pulling samples fast enough, this queue will consume a lot of memory over time. The "max-buffers" property can be used to limit the queue size. The "drop" property controls whether the streaming thread blocks or if older buffers are dropped when the maximum queue size is reached. Note that blocking the streaming thread can negatively affect real-time performance and should be avoided.

If a blocking behaviour is not desirable, setting the "emit-signals" property to TRUE will make appsink emit the "new-sample" and "new-preroll" signals when a sample can be pulled without blocking.

The "caps" property on appsink can be used to control the formats that appsink can receive. This property can contain non-fixed caps, the format of the pulled samples can be obtained by getting the sample caps.

If one of the pull-preroll or pull-sample methods return NULL, the appsink is stopped or in the EOS state. You can check for the EOS state with the "eos" property or with the gst_app_sink_is_eos() method.

The eos signal can also be used to be informed when the EOS state is reached to avoid polling.

Last reviewed on 2008-12-17 (0.10.22)

Details

gst_app_sink_set_caps ()

void                gst_app_sink_set_caps               (GstAppSink *appsink,
                                                         const GstCaps *caps);

Set the capabilities on the appsink element. This function takes a copy of the caps structure. After calling this method, the sink will only accept caps that match caps. If caps is non-fixed, you must check the caps on the buffers to get the actual used caps.

appsink :

a GstAppSink

caps :

caps to set

gst_app_sink_get_caps ()

GstCaps *           gst_app_sink_get_caps               (GstAppSink *appsink);

Get the configured caps on appsink.

appsink :

a GstAppSink

Returns :

the GstCaps accepted by the sink. gst_caps_unref() after usage.

gst_app_sink_is_eos ()

gboolean            gst_app_sink_is_eos                 (GstAppSink *appsink);

Check if appsink is EOS, which is when no more samples can be pulled because an EOS event was received.

This function also returns TRUE when the appsink is not in the PAUSED or PLAYING state.

appsink :

a GstAppSink

Returns :

TRUE if no more samples can be pulled and the appsink is EOS.

gst_app_sink_set_emit_signals ()

void                gst_app_sink_set_emit_signals       (GstAppSink *appsink,
                                                         gboolean emit);

Make appsink emit the "new-preroll" and "new-sample" signals. This option is by default disabled because signal emission is expensive and unneeded when the application prefers to operate in pull mode.

appsink :

a GstAppSink

emit :

the new state

gst_app_sink_get_emit_signals ()

gboolean            gst_app_sink_get_emit_signals       (GstAppSink *appsink);

Check if appsink will emit the "new-preroll" and "new-sample" signals.

appsink :

a GstAppSink

Returns :

TRUE if appsink is emiting the "new-preroll" and "new-sample" signals.

gst_app_sink_set_max_buffers ()

void                gst_app_sink_set_max_buffers        (GstAppSink *appsink,
                                                         guint max);

Set the maximum amount of buffers that can be queued in appsink. After this amount of buffers are queued in appsink, any more buffers will block upstream elements until a sample is pulled from appsink.

appsink :

a GstAppSink

max :

the maximum number of buffers to queue

gst_app_sink_get_max_buffers ()

guint               gst_app_sink_get_max_buffers        (GstAppSink *appsink);

Get the maximum amount of buffers that can be queued in appsink.

appsink :

a GstAppSink

Returns :

The maximum amount of buffers that can be queued.

gst_app_sink_set_drop ()

void                gst_app_sink_set_drop               (GstAppSink *appsink,
                                                         gboolean drop);

Instruct appsink to drop old buffers when the maximum amount of queued buffers is reached.

appsink :

a GstAppSink

drop :

the new state

gst_app_sink_get_drop ()

gboolean            gst_app_sink_get_drop               (GstAppSink *appsink);

Check if appsink will drop old buffers when the maximum amount of queued buffers is reached.

appsink :

a GstAppSink

Returns :

TRUE if appsink is dropping old buffers when the queue is filled.

gst_app_sink_pull_preroll ()

GstSample *         gst_app_sink_pull_preroll           (GstAppSink *appsink);

Get the last preroll sample in appsink. This was the sample that caused the appsink to preroll in the PAUSED state. This sample can be pulled many times and remains available to the application even after EOS.

This function is typically used when dealing with a pipeline in the PAUSED state. Calling this function after doing a seek will give the sample right after the seek position.

Note that the preroll sample will also be returned as the first sample when calling gst_app_sink_pull_sample().

If an EOS event was received before any buffers, this function returns NULL. Use gst_app_sink_is_eos() to check for the EOS condition.

This function blocks until a preroll sample or EOS is received or the appsink element is set to the READY/NULL state.

appsink :

a GstAppSink

Returns :

a GstBuffer or NULL when the appsink is stopped or EOS.

gst_app_sink_pull_sample ()

GstSample *         gst_app_sink_pull_sample            (GstAppSink *appsink);

This function blocks until a sample or EOS becomes available or the appsink element is set to the READY/NULL state.

This function will only return samples when the appsink is in the PLAYING state. All rendered buffers will be put in a queue so that the application can pull samples at its own rate. Note that when the application does not pull samples fast enough, the queued buffers could consume a lot of memory, especially when dealing with raw video frames.

If an EOS event was received before any buffers, this function returns NULL. Use gst_app_sink_is_eos() to check for the EOS condition.

appsink :

a GstAppSink

Returns :

a GstBuffer or NULL when the appsink is stopped or EOS.

GstAppSinkCallbacks

typedef struct {
  void          (*eos)              (GstAppSink *appsink, gpointer user_data);
  GstFlowReturn (*new_preroll)      (GstAppSink *appsink, gpointer user_data);
  GstFlowReturn (*new_sample)       (GstAppSink *appsink, gpointer user_data);
} GstAppSinkCallbacks;

A set of callbacks that can be installed on the appsink with gst_app_sink_set_callbacks().

eos ()

Called when the end-of-stream has been reached. This callback is called from the steaming thread.

new_preroll ()

Called when a new preroll sample is available. This callback is called from the steaming thread. The new preroll sample can be retrieved with gst_app_sink_pull_preroll() either from this callback or from any other thread.

new_sample ()

Called when a new sample is available. This callback is called from the steaming thread. The new sample can be retrieved with gst_app_sink_pull_sample() either from this callback or from any other thread.

gst_app_sink_set_callbacks ()

void                gst_app_sink_set_callbacks          (GstAppSink *appsink,
                                                         GstAppSinkCallbacks *callbacks,
                                                         gpointer user_data,
                                                         GDestroyNotify notify);

Set callbacks which will be executed for each new preroll, new sample and eos. This is an alternative to using the signals, it has lower overhead and is thus less expensive, but also less flexible.

If callbacks are installed, no signals will be emitted for performance reasons.

appsink :

a GstAppSink

callbacks :

the callbacks

user_data :

a user_data argument for the callbacks

notify :

a destroy notify function

See Also

GstSample, GstBaseSink, appsrc