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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
AppSink::pull_sample and AppSink::pull_preroll methods.
These methods block until a sample becomes available in the sink or when the
sink is shut down or reaches EOS. There are also timed variants of these
methods, AppSink::try_pull_sample and AppSink::try_pull_preroll,
which accept a timeout parameter to limit the amount of time to wait.
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 None, the appsink
is stopped or in the EOS state. You can check for the EOS state with the
"eos" property or with the AppSink::is_eos method.
The eos signal can also be used to be informed when the EOS state is reached to avoid polling.
Implements
ElementExt, ObjectExt, ObjectExt
Check if self supports buffer lists.
Feature: v1_12
Returns
true if self supports buffer lists.
Get the configured caps on self.
Returns
the gst::Caps accepted by the sink. gst_caps_unref after usage.
Check if self will drop old buffers when the maximum amount of queued
buffers is reached.
Returns
true if self is dropping old buffers when the queue is
filled.
Check if appsink will emit the "new-preroll" and "new-sample" signals.
Returns
true if self is emiting the "new-preroll" and "new-sample"
signals.
Get the maximum amount of buffers that can be queued in self.
Returns
The maximum amount of buffers that can be queued.
Check if self will wait for all buffers to be consumed when an EOS is
received.
Returns
true if self will wait for all buffers to be consumed when an
EOS is received.
Check if self 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.
Returns
true if no more samples can be pulled and the appsink is EOS.
Get the last preroll sample in self. 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 AppSink::pull_sample.
If an EOS event was received before any buffers, this function returns
None. 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.
Returns
a gst::Sample or NULL when the appsink is stopped or EOS.
Call gst_sample_unref after usage.
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
None. Use gst_app_sink_is_eos () to check for the EOS condition.
Returns
a gst::Sample or NULL when the appsink is stopped or EOS.
Call gst_sample_unref after usage.
Instruct self to enable or disable buffer list support.
For backwards-compatibility reasons applications need to opt in to indicate that they will be able to handle buffer lists.
Feature: v1_12
enable_lists
enable or disable buffer list support
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.
callbacks
the callbacks
user_data
a user_data argument for the callbacks
notify
a destroy notify function
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, or incomplete,
you must check the caps on the samples to get the actual used caps.
caps
caps to set
Instruct self to drop old buffers when the maximum amount of queued
buffers is reached.
drop
the new state
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.
emit
the new state
Set the maximum amount of buffers that can be queued in self. After this
amount of buffers are queued in appsink, any more buffers will block upstream
elements until a sample is pulled from self.
max
the maximum number of buffers to queue
Instruct self to wait for all buffers to be consumed when an EOS is received.
wait
the new state
Get the last preroll sample in self. 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 AppSink::pull_sample.
If an EOS event was received before any buffers or the timeout expires,
this function returns None. Use gst_app_sink_is_eos () to check for the EOS
condition.
This function blocks until a preroll sample or EOS is received, the appsink element is set to the READY/NULL state, or the timeout expires.
Feature: v1_10
timeout
the maximum amount of time to wait for the preroll sample
Returns
a gst::Sample or NULL when the appsink is stopped or EOS or the timeout expires.
Call gst_sample_unref after usage.
This function blocks until a sample or EOS becomes available or the appsink element is set to the READY/NULL state or the timeout expires.
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 or the timeout expires,
this function returns None. Use gst_app_sink_is_eos () to check for the EOS
condition.
Feature: v1_10
timeout
the maximum amount of time to wait for a sample
Returns
a gst::Sample or NULL when the appsink is stopped or EOS or the timeout expires.
Call gst_sample_unref after usage.
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 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. If you don't want to explicitly set the caps, you can use gst_app_src_push_sample. This method gets the caps associated with the sample and sets them on the appsrc replacing any previously set caps (if different from sample's caps).
The main way of handing data to the appsrc element is by calling the
AppSrc::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 mode, in which the application repeatedly calls the push-buffer/push-sample method with a new buffer/sample. 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/push-sample calls. This is a typical mode of operation for the stream-type "stream" and "seekable". Use this mode when implementing various network protocols or hardware devices.
The pull mode, in which the need-data signal triggers the next push-buffer call. This mode is typically used in the "random-access" stream-type. Use this mode 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 has finished pushing data into appsrc, it should call
AppSrc::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
occurs or the state of the appsrc has gone through READY.
Implements
ElementExt, ObjectExt, ObjectExt
Indicates to the appsrc element that the last buffer queued in the element is the last buffer of the stream.
Returns
gst::FlowReturn::Ok when the EOS was successfuly queued.
gst::FlowReturn::Flushing when self is not PAUSED or PLAYING.
Get the configured caps on self.
Returns
the gst::Caps produced by the source. gst_caps_unref after usage.
Get the number of currently queued bytes inside self.
Returns
The number of currently queued bytes.
Get the duration of the stream in nanoseconds. A value of GST_CLOCK_TIME_NONE means that the duration is not known.
Feature: v1_10
Returns
the duration of the stream previously set with AppSrc::set_duration;
Check if appsrc will emit the "new-preroll" and "new-buffer" signals.
Returns
true if self is emitting the "new-preroll" and "new-buffer"
signals.
Retrieve the min and max latencies in min and max respectively.
min
the min latency
max
the min latency
Get the maximum amount of bytes that can be queued in self.
Returns
The maximum amount of bytes that can be queued.
Get the size of the stream in bytes. A value of -1 means that the size is not known.
Returns
the size of the stream previously set with AppSrc::set_size;
Get the stream type. Control the stream type of self
with AppSrc::set_stream_type.
Returns
the stream type.
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.
buffer
a gst::Buffer to push
Returns
gst::FlowReturn::Ok when the buffer was successfuly queued.
gst::FlowReturn::Flushing when self is not PAUSED or PLAYING.
gst::FlowReturn::Eos when EOS occured.
Extract a buffer from the provided sample and adds it to the queue of buffers that the appsrc element will push to its source pad. Any previous caps that were set on appsrc will be replaced by the caps associated with the sample if not equal.
When the block property is TRUE, this function can block until free space becomes available in the queue.
sample
a gst::Sample from which buffer and caps may be
extracted
Returns
gst::FlowReturn::Ok when the buffer was successfuly queued.
gst::FlowReturn::Flushing when self is not PAUSED or PLAYING.
gst::FlowReturn::Eos when EOS occured.
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.
callbacks
the callbacks
user_data
a user_data argument for the callbacks
notify
a destroy notify function
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.
caps
caps to set
Set the duration of the stream in nanoseconds. A value of GST_CLOCK_TIME_NONE means that the duration is not known.
Feature: v1_10
duration
the duration to set
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.
emit
the new state
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.
min
the min latency
max
the min latency
Set the maximum amount of bytes that can be queued in self.
After the maximum amount of bytes are queued, self will emit the
"enough-data" signal.
max
the maximum number of bytes to queue
Set the size of the stream in bytes. A value of -1 means that the size is not known.
size
the size to set
Set the stream type on self. For seekable streams, the "seek" signal must
be connected to.
A stream_type stream
type_
the new state
The stream type.
No seeking is supported in the stream, such as a live stream.
The stream is seekable but seeking might not be very fast, such as data from a webserver.
The stream is seekable and seeking is fast, such as in a local file.