appsrc

appsrc — Easy way for applications to inject buffers into a pipeline

Functions

Types and Values

Object Hierarchy


Includes

#include <gst/app/gstappsrc.h>

Description

The appsrc element can be used by applications to insert data into a GStreamer pipeline. Unlike most GStreamer elements, Appsrc provides external API functions.

appsrc can be used by linking with the libgstapp library to access the methods directly or by using the appsrc action signals.

Before operating appsrc, the caps property must be set to a fixed caps describing the format of the data that will be pushed with appsrc. An exception to this is when pushing buffers with unknown caps, in which case no caps should be set. This is typically true of file-like sources that push raw byte buffers.

The main way of handing data to the appsrc element is by calling the gst_app_src_push_buffer() method or by emitting the push-buffer action signal. This will put the buffer onto a queue from which appsrc will read from in its streaming thread. It is important to note that data transport will not happen from the thread that performed the push-buffer call.

The "max-bytes" property controls how much data can be queued in appsrc before appsrc considers the queue full. A filled internal queue will always signal the "enough-data" signal, which signals the application that it should stop pushing data into appsrc. The "block" property will cause appsrc to block the push-buffer method until free data becomes available again.

When the internal queue is running out of data, the "need-data" signal is emitted, which signals the application that it should start pushing more data into appsrc.

In addition to the "need-data" and "enough-data" signals, appsrc can emit the "seek-data" signal when the "stream-mode" property is set to "seekable" or "random-access". The signal argument will contain the new desired position in the stream expressed in the unit set with the "format" property. After receiving the seek-data signal, the application should push-buffers from the new position.

These signals allow the application to operate the appsrc in two different ways:

The push model, in which the application repeatedly calls the push-buffer method with a new buffer. Optionally, the queue size in the appsrc can be controlled with the enough-data and need-data signals by respectively stopping/starting the push-buffer calls. This is a typical mode of operation for the stream-type "stream" and "seekable". Use this model when implementing various network protocols or hardware devices.

The pull model where the need-data signal triggers the next push-buffer call. This mode is typically used in the "random-access" stream-type. Use this model for file access or other randomly accessable sources. In this mode, a buffer of exactly the amount of bytes given by the need-data signal should be pushed into appsrc.

In all modes, the size property on appsrc should contain the total stream size in bytes. Setting this property is mandatory in the random-access mode. For the stream and seekable modes, setting this property is optional but recommended.

When the application is finished pushing data into appsrc, it should call gst_app_src_end_of_stream() or emit the end-of-stream action signal. After this call, no more buffers can be pushed into appsrc until a flushing seek happened or the state of the appsrc has gone through READY.

Functions

gst_app_src_set_caps ()

void
gst_app_src_set_caps (GstAppSrc *appsrc,
                      const GstCaps *caps);

Set the capabilities on the appsrc element. This function takes a copy of the caps structure. After calling this method, the source will only produce caps that match caps . caps must be fixed and the caps on the buffers must match the caps or left NULL.

Parameters

appsrc

a GstAppSrc

 

caps

caps to set

 

gst_app_src_get_caps ()

GstCaps *
gst_app_src_get_caps (GstAppSrc *appsrc);

Get the configured caps on appsrc .

Parameters

appsrc

a GstAppSrc

 

Returns

the GstCaps produced by the source. gst_caps_unref() after usage.


gst_app_src_get_latency ()

void
gst_app_src_get_latency (GstAppSrc *appsrc,
                         guint64 *min,
                         guint64 *max);

Retrieve the min and max latencies in min and max respectively.

Parameters

appsrc

a GstAppSrc

 

min

the min latency

 

max

the min latency

 

gst_app_src_set_latency ()

void
gst_app_src_set_latency (GstAppSrc *appsrc,
                         guint64 min,
                         guint64 max);

Configure the min and max latency in src . If min is set to -1, the default latency calculations for pseudo-live sources will be used.

Parameters

appsrc

a GstAppSrc

 

min

the min latency

 

max

the min latency

 

gst_app_src_set_size ()

void
gst_app_src_set_size (GstAppSrc *appsrc,
                      gint64 size);

Set the size of the stream in bytes. A value of -1 means that the size is not known.

Parameters

appsrc

a GstAppSrc

 

size

the size to set

 

gst_app_src_get_size ()

gint64
gst_app_src_get_size (GstAppSrc *appsrc);

Get the size of the stream in bytes. A value of -1 means that the size is not known.

Parameters

appsrc

a GstAppSrc

 

Returns

the size of the stream previously set with gst_app_src_set_size();


gst_app_src_set_stream_type ()

void
gst_app_src_set_stream_type (GstAppSrc *appsrc,
                             GstAppStreamType type);

Set the stream type on appsrc . For seekable streams, the "seek" signal must be connected to.

A stream_type stream

Parameters

appsrc

a GstAppSrc

 

type

the new state

 

gst_app_src_get_stream_type ()

GstAppStreamType
gst_app_src_get_stream_type (GstAppSrc *appsrc);

Get the stream type. Control the stream type of appsrc with gst_app_src_set_stream_type().

Parameters

appsrc

a GstAppSrc

 

Returns

the stream type.


gst_app_src_set_max_bytes ()

void
gst_app_src_set_max_bytes (GstAppSrc *appsrc,
                           guint64 max);

Set the maximum amount of bytes that can be queued in appsrc . After the maximum amount of bytes are queued, appsrc will emit the "enough-data" signal.

Parameters

appsrc

a GstAppSrc

 

max

the maximum number of bytes to queue

 

gst_app_src_get_max_bytes ()

guint64
gst_app_src_get_max_bytes (GstAppSrc *appsrc);

Get the maximum amount of bytes that can be queued in appsrc .

Parameters

appsrc

a GstAppSrc

 

Returns

The maximum amount of bytes that can be queued.


gst_app_src_get_current_level_bytes ()

guint64
gst_app_src_get_current_level_bytes (GstAppSrc *appsrc);

Get the number of currently queued bytes inside appsrc .

Parameters

appsrc

a GstAppSrc

 

Returns

The number of currently queued bytes.

Since 1.2


gst_app_src_get_emit_signals ()

gboolean
gst_app_src_get_emit_signals (GstAppSrc *appsrc);

Check if appsrc will emit the "new-preroll" and "new-buffer" signals.

Parameters

appsrc

a GstAppSrc

 

Returns

TRUE if appsrc is emitting the "new-preroll" and "new-buffer" signals.


gst_app_src_set_emit_signals ()

void
gst_app_src_set_emit_signals (GstAppSrc *appsrc,
                              gboolean emit);

Make appsrc 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.

Parameters

appsrc

a GstAppSrc

 

emit

the new state

 

gst_app_src_set_callbacks ()

void
gst_app_src_set_callbacks (GstAppSrc *appsrc,
                           GstAppSrcCallbacks *callbacks,
                           gpointer user_data,
                           GDestroyNotify notify);

Set callbacks which will be executed when data is needed, enough data has been collected or when a seek should be performed. 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.

Parameters

appsrc

a GstAppSrc

 

callbacks

the callbacks

 

user_data

a user_data argument for the callbacks

 

notify

a destroy notify function

 

gst_app_src_push_buffer ()

GstFlowReturn
gst_app_src_push_buffer (GstAppSrc *appsrc,
                         GstBuffer *buffer);

Adds a buffer to the queue of buffers that the appsrc element will push to its source pad. This function takes ownership of the buffer.

When the block property is TRUE, this function can block until free space becomes available in the queue.

Parameters

appsrc

a GstAppSrc

 

buffer

a GstBuffer to push.

[transfer full]

Returns

GST_FLOW_OK when the buffer was successfuly queued. GST_FLOW_FLUSHING when appsrc is not PAUSED or PLAYING. GST_FLOW_EOS when EOS occured.


gst_app_src_end_of_stream ()

GstFlowReturn
gst_app_src_end_of_stream (GstAppSrc *appsrc);

Indicates to the appsrc element that the last buffer queued in the element is the last buffer of the stream.

Parameters

appsrc

a GstAppSrc

 

Returns

GST_FLOW_OK when the EOS was successfuly queued. GST_FLOW_FLUSHING when appsrc is not PAUSED or PLAYING.

Types and Values

enum GstAppStreamType

The stream type.

Members

GST_APP_STREAM_TYPE_STREAM

No seeking is supported in the stream, such as a live stream.

 

GST_APP_STREAM_TYPE_SEEKABLE

The stream is seekable but seeking might not be very fast, such as data from a webserver.

 

GST_APP_STREAM_TYPE_RANDOM_ACCESS

The stream is seekable and seeking is fast, such as in a local file.

 

GstAppSrcCallbacks

typedef struct {
  void      (*need_data)    (GstAppSrc *src, guint length, gpointer user_data);
  void      (*enough_data)  (GstAppSrc *src, gpointer user_data);
  gboolean  (*seek_data)    (GstAppSrc *src, guint64 offset, gpointer user_data);
} GstAppSrcCallbacks;

A set of callbacks that can be installed on the appsrc with gst_app_src_set_callbacks().

Members

need_data ()

Called when the appsrc needs more data. A buffer or EOS should be pushed to appsrc from this thread or another thread. length is just a hint and when it is set to -1, any number of bytes can be pushed into appsrc .

 

enough_data ()

Called when appsrc has enough data. It is recommended that the application stops calling push-buffer until the need_data callback is emitted again to avoid excessive buffer queueing.

 

seek_data ()

Called when a seek should be performed to the offset. The next push-buffer should produce buffers from the new offset . This callback is only called for seekable stream types.

 

See Also

GstBaseSrc, appsink