gstreamermm: Gst::BaseSrc Class Reference

Public Member Functions | Related Functions

# Gst::BaseSrc Class Reference
[gstreamermm Base Classes]

A base class for getrange based source elements. More...

Inherits Gst::Element.

Inherited by Gst::AudioTestSrc, Gst::FakeSrc, Gst::FileSrc, Gst::GioSrc, Gst::GioStreamSrc, and Gst::PushSrc.

Collaboration diagram for Gst::BaseSrc:
[legend]

List of all members.

## Public Member Functions
virtual | ~BaseSrc ()
GstBaseSrc* | gobj ()
| Provides access to the underlying C GObject.
const GstBaseSrc* | gobj () const
| Provides access to the underlying C GObject.
GstBaseSrc* | gobj_copy ()
| Provides access to the underlying C instance. The caller is responsible for unrefing it. Use when directly setting fields in structs.
FlowReturn | wait_playing ()
| If the Gst::BaseSrcClass.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.
bool | is_live () const
| Check if an element is in live mode.
void | set_live (bool live)
| If the element listens to a live source, live should be set to `true`.
void | set_format (Format format)
| Sets the default format of the source.
bool | query_latency (bool& live, ClockTime& min_latency, ClockTime& max_latency) const
| Query the source for the latency parameters.
gulong | get_blocksize () const
| Get the number of bytes that src will push out with each buffer.
void | set_blocksize (gulong blocksize)
| Set the number of bytes that src will push out with each buffer.
bool | get_do_timestamp () const
| Query if src timestamps outgoing buffers based on the current running_time.
void | set_do_timestamp (bool timestamp)
| Configure src to automatically timestamp outgoing buffers based on the current running_time of the pipeline.
bool | new_seamless_segment (gint64 start, gint64 stop, gint64 position)
| Prepare a new seamless segment for emission downstream.
Glib::RefPtr< Gst::Pad > | get_src_pad ()
| Gets the source Gst::Pad object of the element.
Glib::RefPtr< const Gst::Pad > | get_src_pad () const
Glib::PropertyProxy< gulong > | property_blocksize ()
| Size in bytes to read per buffer (-1 = default).
Glib::PropertyProxy_ReadOnly < gulong > | property_blocksize () const
| Size in bytes to read per buffer (-1 = default).
Glib::PropertyProxy< bool > | property_do_timestamp ()
| Apply current stream time to buffers.
Glib::PropertyProxy_ReadOnly < bool > | property_do_timestamp () const
| Apply current stream time to buffers.
Glib::PropertyProxy< int > | property_num_buffers ()
| Number of buffers to output before sending EOS (-1 = unlimited).
Glib::PropertyProxy_ReadOnly< int > | property_num_buffers () const
| Number of buffers to output before sending EOS (-1 = unlimited).
Glib::PropertyProxy< bool > | property_typefind ()
| Run typefind before negotiating.
Glib::PropertyProxy_ReadOnly < bool > | property_typefind () const
| Run typefind before negotiating.
virtual Glib::RefPtr< Gst::Caps > | get_caps_vfunc () const
| Called to get the caps to report.
virtual void | get_times_vfunc (const Glib::RefPtr< Gst::Buffer >& buffer, ClockTime&start, ClockTime&end) const
| Notify subclass of changed output caps.
virtual FlowReturn | create_vfunc (guint64 offset, guint size, Glib::RefPtr< Gst::Buffer >& buffer)
| Return the total size of the resource, in the configured format.
virtual bool | do_seek_vfunc (Gst::Segment& segment)
| Perform seeking on the resource to the indicated segment.
virtual void | fixate_vfunc (const Glib::RefPtr< Gst::Caps >& caps)
| Handle a requested query.
virtual bool | prepare_seek_segment_vfunc (const Glib::RefPtr< Gst::Event >& seek, Gst::Segment& segment)
| Clear the previous unlock request.
## Related Functions
(Note that these are not member functions.)
Glib::RefPtr< Gst::BaseSrc > | wrap (GstBaseSrc* object, bool take_copy=false)
| A Glib::wrap() method for this object.

## Detailed Description

A base class for getrange based source elements.

This is a generice 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 Gst::Format with the set_format() method. The currently set format determines the format of the internal Gst::Segment and any Gst::EVENT_NEWSEGMENT events. The default format for Gst::BaseSrc is Gst::FORMAT_BYTES.

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

- The format is set to Gst::FORMAT_BYTES (default).
- Gst::BaseSrc::is_seekable_vfunc() returns TRUE.

Since GStreamer 0.10.9, any Gst::BaseSrc can enable pull based scheduling at any time by overriding Gst::BaseSrc::check_get_range_vfunc() so that it returns TRUE.

If all the conditions are met for operating in pull mode, Gst::BaseSrc 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:

- Gst::BaseSrc::is_seekable_vfunc() returns TRUE.
- Gst::BaseSrc::query_vfunc() can convert all supported seek formats to the internal format as set with set_format().
- Gst::BaseSrc::do_seek_vfunc() is implemented, performs the seek and returns TRUE.

When the element does not meet the requirements to operate in pull mode, the offset and length in the Gst::BaseSrc::create_vfunc() method should be ignored. It is recommended to subclass Gst::PushSrc 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 Gst::BaseSrc::create_vfunc() function.

Gst::BaseSrc 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 set_live() to activate the live source mode.

A live source does not produce data in the PAUSED state. This means that the Gst::BaseSrc::create_vfunc() 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 since GStreamer 0.10.12 use wait_playing() when the create_vfunc() function was interrupted by a state change to PAUSED.

The Gst::BaseSrc::get_times_vfunc() method can be used to implement pseudo-live sources. It only makes sense to implement the get_times_vfunc() function if the source is a live source. The get_times_vfunc() 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_vfunc() and will report this value as the latency. Subclasses should override the query_vfunc() function when this behaviour is not acceptable.

TODO: Edit below paragraph for C++ and include C++ example from C API (if necessary):

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

## 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.

Since GStreamer 0.10.16 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.

The old behaviour for controlled shutdown introduced since GStreamer 0.10.3 is still available but deprecated as it is dangerous and less flexible.

Last reviewed on 2007-12-19 (0.10.16).

## Constructor & Destructor Documentation

virtual Gst::BaseSrc::~BaseSrc | ( |  | ) | `[virtual]`

## Member Function Documentation

virtual FlowReturn Gst::BaseSrc::create_vfunc | ( | guint64 | offset,
|  | guint | size,
|  | Glib::RefPtr< Gst::Buffer >& | buffer |
| ) |  |  | `[virtual]`

Return the total size of the resource, in the configured format.

Check if the source can seek. Unlock any pending access to the resource. Subclasses should unblock any TODO: Make sure this bool vfunc does not cause execution problems. blocked function ASAP. Override this to implement custom event handling.

virtual bool Gst::BaseSrc::do_seek_vfunc | ( | Gst::Segment& | segment | ) | `[virtual]`

Perform seeking on the resource to the indicated segment.

virtual void Gst::BaseSrc::fixate_vfunc | ( | const Glib::RefPtr< Gst::Caps >& | caps | ) | `[virtual]`

Handle a requested query.

Check whether the source would support pull-based operation if it were to be opened now. This vfunc is optional, but should be implemented if possible to avoid unnecessary start/stop cycles. The default implementation will open and close the resource to find out whether get_range() is supported, and that is usually undesirable. Called during negotiation if caps need fixating. Implement instead of setting a fixate function on the source pad.

gulong Gst::BaseSrc::get_blocksize | ( |  | ) | const

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

Since gstreamermm 0.10:
  .22

Returns:
  The number of bytes pushed with each buffer.

virtual Glib::RefPtr<Gst::Caps> Gst::BaseSrc::get_caps_vfunc | ( |  | ) | const`[virtual]`

Called to get the caps to report.

bool Gst::BaseSrc::get_do_timestamp | ( |  | ) | const

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

Since gstreamermm 0.10:
  .15

Returns:
  `true` if the base class will automatically timestamp outgoing buffers.

Glib::RefPtr<Gst::Pad> Gst::BaseSrc::get_src_pad | ( |  | ) |

Gets the source Gst::Pad object of the element.

Glib::RefPtr<const Gst::Pad> Gst::BaseSrc::get_src_pad | ( |  | ) | const

virtual void Gst::BaseSrc::get_times_vfunc | ( | const Glib::RefPtr< Gst::Buffer >& | buffer,
|  | ClockTime& | start,
|  | ClockTime& | end |
| ) |  |  | const`[virtual]`

Notify subclass of changed output caps.

Negotiated the caps with the peer. Generate and send a new_segment event (UNUSED). Start processing. Subclasses should open resources and prepare to produce data. Stop processing. Subclasses should use this to close resources. 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.

const GstBaseSrc* Gst::BaseSrc::gobj | ( |  | ) | const`[inline]`

Provides access to the underlying C GObject.

Reimplemented from Gst::Element.

Reimplemented in Gst::AudioSrc, Gst::BaseAudioSrc, Gst::CddaBaseSrc, Gst::PushSrc, Gst::AudioTestSrc, Gst::CdParanoiaSrc, Gst::FakeSrc, Gst::GioStreamSrc, Gst::TCPClientSrc, Gst::TCPServerSrc, and Gst::VideoTestSrc.

GstBaseSrc* Gst::BaseSrc::gobj | ( |  | ) | `[inline]`

Provides access to the underlying C GObject.

Reimplemented from Gst::Element.

Reimplemented in Gst::AudioSrc, Gst::BaseAudioSrc, Gst::CddaBaseSrc, Gst::PushSrc, Gst::AudioTestSrc, Gst::CdParanoiaSrc, Gst::FakeSrc, Gst::GioStreamSrc, Gst::TCPClientSrc, Gst::TCPServerSrc, and Gst::VideoTestSrc.

GstBaseSrc* Gst::BaseSrc::gobj_copy | ( |  | ) |

Provides access to the underlying C instance. The caller is responsible for unrefing it. Use when directly setting fields in structs.

Reimplemented from Gst::Element.

Reimplemented in Gst::AudioSrc, Gst::BaseAudioSrc, Gst::CddaBaseSrc, Gst::PushSrc, Gst::AudioTestSrc, Gst::CdParanoiaSrc, Gst::FakeSrc, Gst::GioStreamSrc, Gst::TCPClientSrc, Gst::TCPServerSrc, and Gst::VideoTestSrc.

bool Gst::BaseSrc::is_live | ( |  | ) | const

Check if an element is in live mode.

Returns:
  `true` if element is in live mode.

bool Gst::BaseSrc::new_seamless_segment | ( | gint64 | start,
|  | gint64 | stop,
|  | gint64 | position |
| ) |  |  |

Prepare a new seamless 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 new segment will be the current format of the source, as configured with set_format()

Since gstreamermm 0.10:
  .26

Parameters:

  | start | The new start value for the segment.
  | stop | Stop value for the new segment.
  | position | The position value for the new segent.

Returns:
  `true` if preparation of the seamless segment succeeded.

virtual bool Gst::BaseSrc::prepare_seek_segment_vfunc | ( | const Glib::RefPtr< Gst::Event >& | seek,
|  | Gst::Segment& | segment |
| ) |  |  | `[virtual]`

Clear the previous unlock request.

Subclasses should clear any state they set during unlock_vfunc(), such as clearing command queues. Prepare the Gst::Segment that will be passed to the do_seek_vfunc() 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.

Glib::PropertyProxy<gulong> Gst::BaseSrc::property_blocksize | ( |  | ) |

Size in bytes to read per buffer (-1 = default).

You rarely need to use properties because there are get_ and set_ methods for almost all of them.

Returns:
  A PropertyProxy that allows you to get or set the property of the value, or receive notification when the value of the property changes.

Glib::PropertyProxy_ReadOnly<gulong> Gst::BaseSrc::property_blocksize | ( |  | ) | const

Size in bytes to read per buffer (-1 = default).

You rarely need to use properties because there are get_ and set_ methods for almost all of them.

Returns:
  A PropertyProxy that allows you to get or set the property of the value, or receive notification when the value of the property changes.

Glib::PropertyProxy<bool> Gst::BaseSrc::property_do_timestamp | ( |  | ) |

Apply current stream time to buffers.

You rarely need to use properties because there are get_ and set_ methods for almost all of them.

Returns:
  A PropertyProxy that allows you to get or set the property of the value, or receive notification when the value of the property changes.

Glib::PropertyProxy_ReadOnly<bool> Gst::BaseSrc::property_do_timestamp | ( |  | ) | const

Apply current stream time to buffers.

You rarely need to use properties because there are get_ and set_ methods for almost all of them.

Returns:
  A PropertyProxy that allows you to get or set the property of the value, or receive notification when the value of the property changes.

Glib::PropertyProxy<int> Gst::BaseSrc::property_num_buffers | ( |  | ) |

Number of buffers to output before sending EOS (-1 = unlimited).

You rarely need to use properties because there are get_ and set_ methods for almost all of them.

Returns:
  A PropertyProxy that allows you to get or set the property of the value, or receive notification when the value of the property changes.

Glib::PropertyProxy_ReadOnly<int> Gst::BaseSrc::property_num_buffers | ( |  | ) | const

Number of buffers to output before sending EOS (-1 = unlimited).

You rarely need to use properties because there are get_ and set_ methods for almost all of them.

Returns:
  A PropertyProxy that allows you to get or set the property of the value, or receive notification when the value of the property changes.

Glib::PropertyProxy_ReadOnly<bool> Gst::BaseSrc::property_typefind | ( |  | ) | const

Run typefind before negotiating.

You rarely need to use properties because there are get_ and set_ methods for almost all of them.

Returns:
  A PropertyProxy that allows you to get or set the property of the value, or receive notification when the value of the property changes.

Glib::PropertyProxy<bool> Gst::BaseSrc::property_typefind | ( |  | ) |

Run typefind before negotiating.

You rarely need to use properties because there are get_ and set_ methods for almost all of them.

Returns:
  A PropertyProxy that allows you to get or set the property of the value, or receive notification when the value of the property changes.

bool Gst::BaseSrc::query_latency | ( | bool & | live,
|  | ClockTime& | min_latency,
|  | ClockTime& | max_latency |
| ) |  |  | const

Query the source for the latency parameters.

live will be `true` when src is configured as a live source. min_latency will be set to the difference between the running time and the timestamp of the first buffer. max_latency is always the undefined value of -1.

This function is mostly used by subclasses.

Since gstreamermm 0.10:
  .13

Parameters:

  | live | If the source is live.
  | min_latency | The min latency of the source.
  | max_latency | The max latency of the source.

Returns:
  `true` if the query succeeded.

void Gst::BaseSrc::set_blocksize | ( | gulong | 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.

Since gstreamermm 0.10:
  .22

Parameters:

  | blocksize | The new blocksize in bytes.

void Gst::BaseSrc::set_do_timestamp | ( | bool | 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.

Since gstreamermm 0.10:
  .15

Parameters:

  | timestamp | Enable or disable timestamping.

void Gst::BaseSrc::set_format | ( | Format | format | ) |

Sets the default format of the source.

This will be the format used for sending NEW_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 Gst::BaseSrc.is_seekable() returns `true`.

This function must only be called in states < Gst::STATE_PAUSED.

Since gstreamermm 0.10:
  .1

Parameters:

  | format | The format to use.

void Gst::BaseSrc::set_live | ( | bool | 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:

  | live | New live-mode.

FlowReturn Gst::BaseSrc::wait_playing | ( |  | ) |

If the Gst::BaseSrcClass.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_WRONG_STATE).

Since gstreamermm 0.10:
  .12

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

## Friends And Related Function Documentation

Glib::RefPtr< Gst::BaseSrc > wrap | ( | GstBaseSrc * | object,
|  | bool | take_copy = `false` |
| ) |  |  | `[related]`

A Glib::wrap() method for this object.

Parameters:

  | object | The C instance.
  | take_copy | False if the result should take ownership of the C instance. True if it should take a new copy or ref.

Returns:
  A C++ instance that wraps this C instance.

The documentation for this class was generated from the following file:

- gstreamermm/basesrc.h