appsink

appsink

Synopsis


#include <gst/app/appsink.h>

                    GstAppSink;
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);
GstBuffer *         gst_app_sink_pull_preroll           (GstAppSink *appsink);
GstBuffer *         gst_app_sink_pull_buffer            (GstAppSink *appsink);

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 buffers from appsink is by using the gst_app_sink_pull_buffer() and gst_app_sink_pull_preroll() methods. These methods block until a buffer 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 buffers 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-buffer" and "new-preroll" signals when a buffer 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 buffers can be obtained by getting the buffer caps.

If one of the pull-preroll or pull-buffer 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.

Details

GstAppSink

typedef struct {
  GstBaseSink basesink;
} GstAppSink;


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

Since 0.10.22


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.

Since 0.10.22


gst_app_sink_is_eos ()

gboolean            gst_app_sink_is_eos                 (GstAppSink *appsink);

Check if appsink is EOS, which is when no more buffers 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 buffers can be pulled and the appsink is EOS.

Since 0.10.22


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-buffer" 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

Since 0.10.22


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-buffer" signals.

appsink :

a GstAppSink

Returns :

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

Since 0.10.22


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 buffer is pulled from appsink.

appsink :

a GstAppSink

max :

the maximum number of buffers to queue

Since 0.10.22


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.

Since 0.10.22


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

Since 0.10.22


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.

Since 0.10.22


gst_app_sink_pull_preroll ()

GstBuffer *         gst_app_sink_pull_preroll           (GstAppSink *appsink);

Get the last preroll buffer in appsink. This was the buffer that caused the appsink to preroll in the PAUSED state. This buffer 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 buffer right after the seek position.

Note that the preroll buffer will also be returned as the first buffer when calling gst_app_sink_pull_buffer().

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 buffer 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.

Since 0.10.22


gst_app_sink_pull_buffer ()

GstBuffer *         gst_app_sink_pull_buffer            (GstAppSink *appsink);

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

This function will only return buffers when the appsink is in the PLAYING state. All rendered buffers will be put in a queue so that the application can pull buffers at its own rate. Note that when the application does not pull buffers 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.

Since 0.10.22

See Also

#GstBaseSink, appsrc