GstBaseSrc

This is a generic base class for source elements. The following types of sources are supported:

  • random access sources like files
  • seekable sources
  • live sources

The source can be configured to operate in any GstFormat with the gst_base_src_set_format method. The currently set format determines the format of the internal GstSegment and any GST_EVENT_SEGMENT events. The default format for GstBaseSrc is GST_FORMAT_BYTES.

GstBaseSrc always supports push mode scheduling. If the following conditions are met, it also supports pull mode scheduling:

If all the conditions are met for operating in pull mode, GstBaseSrc is automatically seekable in push mode as well. The following conditions must be met to make the element seekable in push mode when the format is not GST_FORMAT_BYTES:

When the element does not meet the requirements to operate in pull mode, the offset and length in the create method should be ignored. It is recommended to subclass GstPushSrc instead, in this situation. If the element can operate in pull mode but only with specific offsets and lengths, it is allowed to generate an error when the wrong values are passed to the create function.

GstBaseSrc has support for live sources. Live sources are sources that when paused discard data, such as audio or video capture devices. A typical live source also produces data at a fixed rate and thus provides a clock to publish this rate. Use gst_base_src_set_live to activate the live source mode.

A live source does not produce data in the PAUSED state. This means that the create method will not be called in PAUSED but only in PLAYING. To signal the pipeline that the element will not produce data, the return value from the READY to PAUSED state will be GST_STATE_CHANGE_NO_PREROLL.

A typical live source will timestamp the buffers it creates with the current running time of the pipeline. This is one reason why a live source can only produce data in the PLAYING state, when the clock is actually distributed and running.

Live sources that synchronize and block on the clock (an audio source, for example) can use gst_base_src_wait_playing when the create function was interrupted by a state change to PAUSED.

The get_times method can be used to implement pseudo-live sources. It only makes sense to implement the get_times function if the source is a live source. The get_times function should return timestamps starting from 0, as if it were a non-live source. The base class will make sure that the timestamps are transformed into the current running_time. The base source will then wait for the calculated running_time before pushing out the buffer.

For live sources, the base class will by default report a latency of 0. For pseudo live sources, the base class will by default measure the difference between the first buffer timestamp and the start time of get_times and will report this value as the latency. Subclasses should override the query function when this behaviour is not acceptable.

There is only support in GstBaseSrc for exactly one source pad, which should be named "src". A source implementation (subclass of GstBaseSrc) should install a pad template in its class_init function, like so:

 static void
 my_element_class_init (GstMyElementClass *klass)
 {
   GstElementClass *gstelement_class = GST_ELEMENT_CLASS (klass);
   // srctemplate should be a #GstStaticPadTemplate with direction
   // %GST_PAD_SRC and name "src"
   gst_element_class_add_static_pad_template (gstelement_class, &srctemplate);

   gst_element_class_set_static_metadata (gstelement_class,
      "Source name",
      "Source",
      "My Source element",
      "The author <my.sink@my.email>");
 }

Controlled shutdown of live sources in applications

Applications that record from a live source may want to stop recording in a controlled way, so that the recording is stopped, but the data already in the pipeline is processed to the end (remember that many live sources would go on recording forever otherwise). For that to happen the application needs to make the source stop recording and send an EOS event down the pipeline. The application would then wait for an EOS message posted on the pipeline's bus to know when all data has been processed and the pipeline can safely be stopped.

An application may send an EOS event to a source element to make it perform the EOS logic (send EOS event downstream or post a GST_MESSAGE_SEGMENT_DONE on the bus). This can typically be done with the gst_element_send_event function on the element or its parent bin.

After the EOS has been sent to the element, the application should wait for an EOS message to be posted on the pipeline's bus. Once this EOS message is received, it may safely shut down the entire pipeline.

GstBaseSrc

GObject
    ╰──GInitiallyUnowned
        ╰──GstObject
            ╰──GstElement
                ╰──GstBaseSrc
                    ╰──GstPushSrc

The opaque GstBaseSrc data structure.

Members

element (GstElement) –
No description available
srcpad (GstPad *) –
No description available
live_lock (GMutex) –
No description available
live_cond (GCond) –
No description available
is_live (gboolean) –
No description available
live_running (gboolean) –
No description available
blocksize (guint) –
No description available
can_activate_push (gboolean) –
No description available
random_access (gboolean) –
No description available
clock_id (GstClockID) –
No description available
segment (GstSegment) –
No description available
need_newsegment (gboolean) –
No description available
num_buffers (gint) –
No description available
num_buffers_left (gint) –
No description available
typefind (gboolean) –
No description available
running (gboolean) –
No description available
pending_seek (GstEvent *) –
No description available
priv (GstBaseSrcPrivate*) –
No description available

Class structure

GstBaseSrcClass

Subclasses can override any of the available virtual methods or not, as needed. At the minimum, the create method should be overridden to produce buffers.

Fields
parent_class (GstElementClass) –

Element parent class


Methods

gst_base_src_get_allocator

gst_base_src_get_allocator (GstBaseSrc * src,
                            GstAllocator ** allocator,
                            GstAllocationParams * params)

Lets GstBaseSrc sub-classes to know the memory allocator used by the base class and its params.

Unref the allocator after usage.

Parameters:

src

a GstBaseSrc

allocator ( [out][optional][nullable][transfer: full])

the GstAllocator used

params ( [out][optional])

the GstAllocationParams of allocator


gst_base_src_get_blocksize

guint
gst_base_src_get_blocksize (GstBaseSrc * src)

Get the number of bytes that src will push out with each buffer.

Parameters:

src

the source

Returns

the number of bytes pushed with each buffer.


gst_base_src_get_buffer_pool

GstBufferPool *
gst_base_src_get_buffer_pool (GstBaseSrc * src)

Parameters:

src

a GstBaseSrc

Returns ( [nullable][transfer: full])

the instance of the GstBufferPool used by the src; unref it after usage.


gst_base_src_get_do_timestamp

gboolean
gst_base_src_get_do_timestamp (GstBaseSrc * src)

Query if src timestamps outgoing buffers based on the current running_time.

Parameters:

src

the source

Returns

TRUE if the base class will automatically timestamp outgoing buffers.


gst_base_src_is_async

gboolean
gst_base_src_is_async (GstBaseSrc * src)

Get the current async behaviour of src. See also gst_base_src_set_async.

Parameters:

src

base source instance

Returns

TRUE if src is operating in async mode.


gst_base_src_is_live

gboolean
gst_base_src_is_live (GstBaseSrc * src)

Check if an element is in live mode.

Parameters:

src

base source instance

Returns

TRUE if element is in live mode.


gst_base_src_negotiate

gboolean
gst_base_src_negotiate (GstBaseSrc * src)

Negotiates src pad caps with downstream elements. Unmarks GST_PAD_FLAG_NEED_RECONFIGURE in any case. But marks it again if negotiate fails.

Do not call this in the fill vmethod. Call this in create or in alloc, before any buffer is allocated.

Parameters:

src

base source instance

Returns

TRUE if the negotiation succeeded, else FALSE.

Since : 1.18


gst_base_src_new_segment

gboolean
gst_base_src_new_segment (GstBaseSrc * src,
                          const GstSegment * segment)

Prepare a new segment for emission downstream. This function must only be called by derived sub-classes, and only from the create function, as the stream-lock needs to be held.

The format for the segment must be identical with the current format of the source, as configured with gst_base_src_set_format.

The format of src must not be GST_FORMAT_UNDEFINED and the format should be configured via gst_base_src_set_format before calling this method.

Parameters:

src

a GstBaseSrc

segment

a pointer to a GstSegment

Returns

TRUE if preparation of new segment succeeded.

Since : 1.18


gst_base_src_push_segment

gboolean
gst_base_src_push_segment (GstBaseSrc * src,
                           const GstSegment * segment)

Send a new segment downstream. This function must only be called by derived sub-classes, and only from the create function, as the stream-lock needs to be held. This method also requires that an out caps has been configured, so gst_base_src_set_caps needs to have been called before.

The format for the segment must be identical with the current format of the source, as configured with gst_base_src_set_format.

The format of src must not be GST_FORMAT_UNDEFINED and the format should be configured via gst_base_src_set_format before calling this method.

This is a variant of gst_base_src_new_segment sending the segment right away, which can be useful to ensure events ordering.

Parameters:

src

a GstBaseSrc

segment

a pointer to a GstSegment

Returns

TRUE if sending of new segment succeeded.

Since : 1.24


gst_base_src_query_latency

gboolean
gst_base_src_query_latency (GstBaseSrc * src,
                            gboolean * live,
                            GstClockTime * min_latency,
                            GstClockTime * max_latency)

Query the source for the latency parameters. live will be TRUE when src is configured as a live source. min_latency and max_latency will be set to the difference between the running time and the timestamp of the first buffer.

This function is mostly used by subclasses.

Parameters:

src

the source

live ( [out][allow-none])

if the source is live

min_latency ( [out][allow-none])

the min latency of the source

max_latency ( [out][allow-none])

the max latency of the source

Returns

TRUE if the query succeeded.


gst_base_src_set_async

gst_base_src_set_async (GstBaseSrc * src,
                        gboolean async)

Configure async behaviour in src, no state change will block. The open, close, start, stop, play and pause virtual methods will be executed in a different thread and are thus allowed to perform blocking operations. Any blocking operation should be unblocked with the unlock vmethod.

Parameters:

src

base source instance

async

new async mode


gst_base_src_set_automatic_eos

gst_base_src_set_automatic_eos (GstBaseSrc * src,
                                gboolean automatic_eos)

If automatic_eos is TRUE, src will automatically go EOS if a buffer after the total size is returned. By default this is TRUE but sources that can't return an authoritative size and only know that they're EOS when trying to read more should set this to FALSE.

When src operates in GST_FORMAT_TIME, GstBaseSrc will send an EOS when a buffer outside of the currently configured segment is pushed if automatic_eos is TRUE. Since 1.16, if automatic_eos is FALSE an EOS will be pushed only when the create implementation returns GST_FLOW_EOS.

Parameters:

src

base source instance

automatic_eos

automatic eos

Since : 1.4


gst_base_src_set_blocksize

gst_base_src_set_blocksize (GstBaseSrc * src,
                            guint blocksize)

Set the number of bytes that src will push out with each buffer. When blocksize is set to -1, a default length will be used.

Parameters:

src

the source

blocksize

the new blocksize in bytes


gst_base_src_set_caps

gboolean
gst_base_src_set_caps (GstBaseSrc * src,
                       GstCaps * caps)

Set new caps on the basesrc source pad.

Parameters:

src

a GstBaseSrc

caps ( [transfer: none])

a GstCaps

Returns

TRUE if the caps could be set


gst_base_src_set_do_timestamp

gst_base_src_set_do_timestamp (GstBaseSrc * src,
                               gboolean timestamp)

Configure src to automatically timestamp outgoing buffers based on the current running_time of the pipeline. This property is mostly useful for live sources.

Parameters:

src

the source

timestamp

enable or disable timestamping


gst_base_src_set_dynamic_size

gst_base_src_set_dynamic_size (GstBaseSrc * src,
                               gboolean dynamic)

If not dynamic, size is only updated when needed, such as when trying to read past current tracked size. Otherwise, size is checked for upon each read.

Parameters:

src

base source instance

dynamic

new dynamic size mode


gst_base_src_set_format

gst_base_src_set_format (GstBaseSrc * src,
                         GstFormat format)

Sets the default format of the source. This will be the format used for sending SEGMENT events and for performing seeks.

If a format of GST_FORMAT_BYTES is set, the element will be able to operate in pull mode if the is_seekable returns TRUE.

This function must only be called in states < GST_STATE_PAUSED.

Parameters:

src

base source instance

format

the format to use


gst_base_src_set_live

gst_base_src_set_live (GstBaseSrc * src,
                       gboolean live)

If the element listens to a live source, live should be set to TRUE.

A live source will not produce data in the PAUSED state and will therefore not be able to participate in the PREROLL phase of a pipeline. To signal this fact to the application and the pipeline, the state change return value of the live source will be GST_STATE_CHANGE_NO_PREROLL.

Parameters:

src

base source instance

live

new live-mode


gst_base_src_start_complete

gst_base_src_start_complete (GstBaseSrc * basesrc,
                             GstFlowReturn ret)

Complete an asynchronous start operation. When the subclass overrides the start method, it should call gst_base_src_start_complete when the start operation completes either from the same thread or from an asynchronous helper thread.

Parameters:

basesrc

base source instance

ret

a GstFlowReturn


gst_base_src_start_wait

GstFlowReturn
gst_base_src_start_wait (GstBaseSrc * basesrc)

Wait until the start operation completes.

Parameters:

basesrc

base source instance

Returns

a GstFlowReturn.


gst_base_src_submit_buffer_list

gst_base_src_submit_buffer_list (GstBaseSrc * src,
                                 GstBufferList * buffer_list)

Subclasses can call this from their create virtual method implementation to submit a buffer list to be pushed out later. This is useful in cases where the create function wants to produce multiple buffers to be pushed out in one go in form of a GstBufferList, which can reduce overhead drastically, especially for packetised inputs (for data streams where the packetisation/chunking is not important it is usually more efficient to return larger buffers instead).

Subclasses that use this function from their create function must return GST_FLOW_OK and no buffer from their create virtual method implementation. If a buffer is returned after a buffer list has also been submitted via this function the behaviour is undefined.

Subclasses must only call this function once per create function call and subclasses must only call this function when the source operates in push mode.

Parameters:

src

a GstBaseSrc

buffer_list ( [transfer: full])

a GstBufferList

Since : 1.14


gst_base_src_wait_playing

GstFlowReturn
gst_base_src_wait_playing (GstBaseSrc * src)

If the create method performs its own synchronisation against the clock it must unblock when going from PLAYING to the PAUSED state and call this method before continuing to produce the remaining data.

This function will block until a state change to PLAYING happens (in which case this function returns GST_FLOW_OK) or the processing must be stopped due to a state change to READY or a FLUSH event (in which case this function returns GST_FLOW_FLUSHING).

Parameters:

src

the src

Returns

GST_FLOW_OK if src is PLAYING and processing can continue. Any other return value should be returned from the create vmethod.


Properties

automatic-eos

“automatic-eos” gboolean

See gst_base_src_set_automatic_eos

Flags : Read / Write

Since : 1.24


blocksize

“blocksize” guint

Flags : Read / Write


do-timestamp

“do-timestamp” gboolean

Flags : Read / Write


num-buffers

“num-buffers” gint

Flags : Read / Write


typefind

“typefind” gboolean

Flags : Read / Write


Virtual Methods

alloc

GstFlowReturn
alloc (GstBaseSrc * src,
       guint64 offset,
       guint size,
       GstBuffer ** buf)

Ask the subclass to allocate a buffer with for offset and size. The default implementation will create a new buffer from the negotiated allocator.

Parameters:

src
No description available
offset
No description available
size
No description available
buf
No description available
Returns
No description available

create

GstFlowReturn
create (GstBaseSrc * src,
        guint64 offset,
        guint size,
        GstBuffer ** buf)

Ask the subclass to create a buffer with offset and size. When the subclass returns GST_FLOW_OK, it MUST return a buffer of the requested size unless fewer bytes are available because an EOS condition is near. No buffer should be returned when the return value is different from GST_FLOW_OK. A return value of GST_FLOW_EOS signifies that the end of stream is reached. The default implementation will call alloc and then call fill.

Parameters:

src
No description available
offset
No description available
size
No description available
buf
No description available
Returns
No description available

decide_allocation

gboolean
decide_allocation (GstBaseSrc * src,
                   GstQuery * query)

configure the allocation query

Parameters:

src
No description available
query
No description available
Returns
No description available

do_seek

gboolean
do_seek (GstBaseSrc * src,
         GstSegment * segment)

Perform seeking on the resource to the indicated segment.

Parameters:

src
No description available
segment
No description available
Returns
No description available

event

gboolean
event (GstBaseSrc * src,
       GstEvent * event)

Override this to implement custom event handling.

Parameters:

src
No description available
event
No description available
Returns
No description available

fill

GstFlowReturn
fill (GstBaseSrc * src,
      guint64 offset,
      guint size,
      GstBuffer * buf)

Ask the subclass to fill the buffer with data for offset and size. The passed buffer is guaranteed to hold the requested amount of bytes.

Parameters:

src
No description available
offset
No description available
size
No description available
buf
No description available
Returns
No description available

fixate

GstCaps *
fixate (GstBaseSrc * src,
        GstCaps * caps)

Called during negotiation if caps need fixating. Implement instead of setting a fixate function on the source pad.

Parameters:

src
No description available
caps
No description available
Returns
No description available

get_caps

GstCaps *
get_caps (GstBaseSrc * src,
          GstCaps * filter)

Called to get the caps to report

Parameters:

src
No description available
filter
No description available
Returns
No description available

get_size

gboolean
get_size (GstBaseSrc * src,
          guint64 * size)

Return the total size of the resource, in the format set by gst_base_src_set_format.

Parameters:

src
No description available
size
No description available
Returns
No description available

get_times

get_times (GstBaseSrc * src,
           GstBuffer * buffer,
           GstClockTime * start,
           GstClockTime * end)

Given a buffer, return the start and stop time when it should be pushed out. The base class will sync on the clock using these times.

Parameters:

src
No description available
buffer
No description available
start
No description available
end
No description available

is_seekable

gboolean
is_seekable (GstBaseSrc * src)

Check if the source can seek

Parameters:

src
No description available
Returns
No description available

negotiate

gboolean
negotiate (GstBaseSrc * src)

Negotiated the caps with the peer.

Parameters:

src
No description available
Returns
No description available

prepare_seek_segment

gboolean
prepare_seek_segment (GstBaseSrc * src,
                      GstEvent * seek,
                      GstSegment * segment)

Prepare the GstSegment that will be passed to the do_seek vmethod for executing a seek request. Sub-classes should override this if they support seeking in formats other than the configured native format. By default, it tries to convert the seek arguments to the configured native format and prepare a segment in that format.

Parameters:

src
No description available
seek
No description available
segment
No description available
Returns
No description available

query

gboolean
query (GstBaseSrc * src,
       GstQuery * query)

Handle a requested query.

Parameters:

src
No description available
query
No description available
Returns
No description available

set_caps

gboolean
set_caps (GstBaseSrc * src,
          GstCaps * caps)

Notify subclass of changed output caps

Parameters:

src
No description available
caps
No description available
Returns
No description available

start

gboolean
start (GstBaseSrc * src)

Start processing. Subclasses should open resources and prepare to produce data. Implementation should call gst_base_src_start_complete when the operation completes, either from the current thread or any other thread that finishes the start operation asynchronously.

Parameters:

src
No description available
Returns
No description available

stop

gboolean
stop (GstBaseSrc * src)

Stop processing. Subclasses should use this to close resources.

Parameters:

src
No description available
Returns
No description available

unlock

gboolean
unlock (GstBaseSrc * src)

Unlock any pending access to the resource. Subclasses should unblock any blocked function ASAP. In particular, any create() function in progress should be unblocked and should return GST_FLOW_FLUSHING. Any future create function call should also return GST_FLOW_FLUSHING until the unlock_stop function has been called.

Parameters:

src
No description available
Returns
No description available

unlock_stop

gboolean
unlock_stop (GstBaseSrc * src)

Clear the previous unlock request. Subclasses should clear any state they set during unlock, such as clearing command queues.

Parameters:

src
No description available
Returns
No description available

Function Macros

GST_BASE_SRC_CAST

#define GST_BASE_SRC_CAST(obj)          ((GstBaseSrc *)(obj))

GST_BASE_SRC_IS_STARTED

#define GST_BASE_SRC_IS_STARTED(obj)  GST_OBJECT_FLAG_IS_SET ((obj), GST_BASE_SRC_FLAG_STARTED)

GST_BASE_SRC_IS_STARTING

#define GST_BASE_SRC_IS_STARTING(obj) GST_OBJECT_FLAG_IS_SET ((obj), GST_BASE_SRC_FLAG_STARTING)

GST_BASE_SRC_PAD

#define GST_BASE_SRC_PAD(obj)                 (GST_BASE_SRC_CAST (obj)->srcpad)

Gives the pointer to the GstPad object of the element.

Parameters:

obj

base source instance


Enumerations

GstBaseSrcFlags

The GstElement flags that a basesrc element may have.

Members
GST_BASE_SRC_FLAG_STARTING (16384) –

has source is starting

GST_BASE_SRC_FLAG_STARTED (32768) –

has source been started

GST_BASE_SRC_FLAG_LAST (1048576) –

offset to define more flags


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