GstBase.BaseTransform

g GObject.InitiallyUnowned GObject.InitiallyUnowned Gst.Object Gst.Object GObject.InitiallyUnowned->Gst.Object GObject.Object GObject.Object GObject.Object->GObject.InitiallyUnowned Gst.Element Gst.Element GstBase.BaseTransform GstBase.BaseTransform Gst.Element->GstBase.BaseTransform Gst.Object->Gst.Element

Subclasses

None

Methods

Inherited

Gst.Element (81), Gst.Object (27), GObject.Object (37)

Structs

Gst.ElementClass (10), GObject.ObjectClass (5)

get_allocator ()

get_buffer_pool ()

is_in_place ()

is_passthrough ()

is_qos_enabled ()

reconfigure ()

reconfigure_sink ()

reconfigure_src ()

set_gap_aware (gap_aware)

set_in_place (in_place)

set_passthrough (passthrough)

set_prefer_passthrough (prefer_passthrough)

set_qos_enabled (enabled)

update_qos (proportion, diff, timestamp)

update_src_caps (updated_caps)

Virtual Methods

Inherited

Gst.Element (16), Gst.Object (1), GObject.Object (7)

do_accept_caps (direction, caps)

do_before_transform (buffer)

do_copy_metadata (input, outbuf)

do_decide_allocation (query)

do_filter_meta (query, api, params)

do_fixate_caps (direction, caps, othercaps)

do_generate_output ()

do_get_unit_size (caps)

do_prepare_output_buffer (input)

do_propose_allocation (decide_query, query)

do_query (direction, query)

do_set_caps (incaps, outcaps)

do_sink_event (event)

do_src_event (event)

do_start ()

do_stop ()

do_submit_input_buffer (is_discont, input)

do_transform (inbuf, outbuf)

do_transform_caps (direction, caps, filter)

do_transform_ip (buf)

do_transform_meta (outbuf, meta, inbuf)

do_transform_size (direction, caps, size, othercaps)

Properties

Inherited

Gst.Object (2)

Name

Type

Flags

Short Description

qos

bool

r/w

Handle Quality-of-Service events

Signals

Inherited

Gst.Element (3), Gst.Object (1), GObject.Object (1)

Fields

Inherited

Gst.Element (3), Gst.Object (1), GObject.Object (1)

Name

Type

Access

Description

element

Gst.Element

r

have_segment

bool

r

queued_buf

Gst.Buffer

r

segment

Gst.Segment

r

sinkpad

Gst.Pad

r

srcpad

Gst.Pad

r

Class Details

class GstBase.BaseTransform(**kwargs)
Bases

Gst.Element

Abstract

Yes

Structure

GstBase.BaseTransformClass

This base class is for filter elements that process data. Elements that are suitable for implementation using GstBase.BaseTransform are ones where the size and caps of the output is known entirely from the input caps and buffer sizes. These include elements that directly transform one buffer into another, modify the contents of a buffer in-place, as well as elements that collate multiple input buffers into one output buffer, or that expand one input buffer into multiple output buffers. See below for more concrete use cases.

It provides for:

  • one sinkpad and one srcpad

  • Possible formats on sink and source pad implemented with custom transform_caps function. By default uses same format on sink and source.

  • Handles state changes

  • Does flushing

  • Push mode

  • Pull mode if the sub-class transform can operate on arbitrary data

Use Cases
Passthrough mode
  • Element has no interest in modifying the buffer. It may want to inspect it, in which case the element should have a transform_ip function. If there is no transform_ip function in passthrough mode, the buffer is pushed intact.

  • The GstBase.BaseTransformClass.passthrough_on_same_caps variable will automatically set/unset passthrough based on whether the element negotiates the same caps on both pads.

  • GstBase.BaseTransformClass.passthrough_on_same_caps on an element that doesn’t implement a transform_caps function is useful for elements that only inspect data (such as level)

  • Example elements

    • Level

    • Videoscale, audioconvert, videoconvert, audioresample in certain modes.

Modifications in-place - input buffer and output buffer are the same thing.
  • The element must implement a transform_ip function.

  • Output buffer size must <= input buffer size

  • If the always_in_place flag is set, non-writable buffers will be copied and passed to the transform_ip function, otherwise a new buffer will be created and the transform function called.

  • Incoming writable buffers will be passed to the transform_ip function immediately.

  • only implementing transform_ip and not transform implies always_in_place = True

    • Example elements:

      • Volume

      • Audioconvert in certain modes (signed/unsigned conversion)

      • videoconvert in certain modes (endianness swapping)

Modifications only to the caps/metadata of a buffer
  • The element does not require writable data, but non-writable buffers should be subbuffered so that the meta-information can be replaced.

  • Elements wishing to operate in this mode should replace the prepare_output_buffer method to create subbuffers of the input buffer and set always_in_place to True

  • Example elements

    • Capsfilter when setting caps on outgoing buffers that have none.

    • identity when it is going to re-timestamp buffers by datarate.

Normal mode
  • always_in_place flag is not set, or there is no transform_ip function

  • Element will receive an input buffer and output buffer to operate on.

  • Output buffer is allocated by calling the prepare_output_buffer function.

  • Example elements:

    • Videoscale, videoconvert, audioconvert when doing scaling/conversions

Special output buffer allocations
  • Elements which need to do special allocation of their output buffers beyond allocating output buffers via the negotiated allocator or buffer pool should implement the prepare_output_buffer method.

  • Example elements:

    • efence

Sub-class settable flags on GstBase.BaseTransform
  • passthrough

    • Implies that in the current configuration, the sub-class is not interested in modifying the buffers.

    • Elements which are always in passthrough mode whenever the same caps has been negotiated on both pads can set the class variable passthrough_on_same_caps to have this behaviour automatically.

  • always_in_place

    • Determines whether a non-writable buffer will be copied before passing to the transform_ip function.

    • Implied True if no transform function is implemented.

    • Implied False if ONLY transform function is implemented.

get_allocator()
Returns

allocator

the Gst.Allocator used

params

the Gst.AllocationParams of allocator

Return type

(allocator: Gst.Allocator or None, params: Gst.AllocationParams)

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

Unref the allocator after use.

get_buffer_pool()
Returns

the instance of the Gst.BufferPool used by self; free it after use

Return type

Gst.BufferPool or None

is_in_place()
Returns

True if the transform is configured in in_place mode.

MT safe.

Return type

bool

See if self is configured as a in_place transform.

is_passthrough()
Returns

True if the transform is configured in passthrough mode.

MT safe.

Return type

bool

See if self is configured as a passthrough transform.

is_qos_enabled()
Returns

True if QoS is enabled.

MT safe.

Return type

bool

Queries if the transform will handle QoS.

reconfigure()
Returns

True if the negotiation succeeded, else False.

Return type

bool

Negotiates src pad caps with downstream elements if the source pad is marked as needing reconfiguring. Unmarks Gst.PadFlags.NEED_RECONFIGURE in any case. But marks it again if negotiation fails.

Do not call this in the #GstBaseTransformClass::transform or #GstBaseTransformClass::transform_ip vmethod. Call this in #GstBaseTransformClass::submit_input_buffer, #GstBaseTransformClass::prepare_output_buffer or in #GstBaseTransformClass::generate_output _before_ any output buffer is allocated.

It will be default be called when handling an ALLOCATION query or at the very beginning of the default #GstBaseTransformClass::submit_input_buffer implementation.

New in version 1.18.

reconfigure_sink()

Instructs self to request renegotiation upstream. This function is typically called after properties on the transform were set that influence the input format.

reconfigure_src()

Instructs self to renegotiate a new downstream transform on the next buffer. This function is typically called after properties on the transform were set that influence the output format.

set_gap_aware(gap_aware)
Parameters

gap_aware (bool) – New state

If gap_aware is False (the default), output buffers will have the Gst.BufferFlags.GAP flag unset.

If set to True, the element must handle output buffers with this flag set correctly, i.e. it can assume that the buffer contains neutral data but must unset the flag if the output is no neutral data.

MT safe.

set_in_place(in_place)
Parameters

in_place (bool) – Boolean value indicating that we would like to operate on in_place buffers.

Determines whether a non-writable buffer will be copied before passing to the transform_ip function.

  • Always True if no transform function is implemented.

  • Always False if ONLY transform function is implemented.

MT safe.

set_passthrough(passthrough)
Parameters

passthrough (bool) – boolean indicating passthrough mode.

Set passthrough mode for this filter by default. This is mostly useful for filters that do not care about negotiation.

Always True for filters which don’t implement either a transform or transform_ip or generate_output method.

MT safe.

set_prefer_passthrough(prefer_passthrough)
Parameters

prefer_passthrough (bool) – New state

If prefer_passthrough is True (the default), self will check and prefer passthrough caps from the list of caps returned by the transform_caps vmethod.

If set to False, the element must order the caps returned from the transform_caps function in such a way that the preferred format is first in the list. This can be interesting for transforms that can do passthrough transforms but prefer to do something else, like a capsfilter.

MT safe.

New in version 1.0.1.

set_qos_enabled(enabled)
Parameters

enabled (bool) – new state

Enable or disable QoS handling in the transform.

MT safe.

update_qos(proportion, diff, timestamp)
Parameters
  • proportion (float) – the proportion

  • diff (int) – the diff against the clock

  • timestamp (int) – the timestamp of the buffer generating the QoS expressed in running_time.

Set the QoS parameters in the transform. This function is called internally when a QOS event is received but subclasses can provide custom information when needed.

MT safe.

update_src_caps(updated_caps)
Parameters

updated_caps (Gst.Caps) – An updated version of the srcpad caps to be pushed downstream

Returns

True if the caps could be sent downstream False otherwise

Return type

bool

Updates the srcpad caps and sends the caps downstream. This function can be used by subclasses when they have already negotiated their caps but found a change in them (or computed new information). This way, they can notify downstream about that change without losing any buffer.

New in version 1.6.

do_accept_caps(direction, caps) virtual
Parameters
Return type

bool

do_before_transform(buffer) virtual
Parameters

buffer (Gst.Buffer) –

do_copy_metadata(input, outbuf) virtual
Parameters
Return type

bool

do_decide_allocation(query) virtual
Parameters

query (Gst.Query) –

Return type

bool

do_filter_meta(query, api, params) virtual
Parameters
Return type

bool

do_fixate_caps(direction, caps, othercaps) virtual
Parameters
Return type

Gst.Caps

do_generate_output() virtual
Return type

(Gst.FlowReturn, outbuf: Gst.Buffer)

do_get_unit_size(caps) virtual
Parameters

caps (Gst.Caps) –

Return type

(bool, size: int)

do_prepare_output_buffer(input) virtual
Parameters

input (Gst.Buffer) –

Return type

(Gst.FlowReturn, outbuf: Gst.Buffer)

do_propose_allocation(decide_query, query) virtual
Parameters
Return type

bool

do_query(direction, query) virtual
Parameters
Return type

bool

do_set_caps(incaps, outcaps) virtual
Parameters
Return type

bool

do_sink_event(event) virtual
Parameters

event (Gst.Event) –

Return type

bool

do_src_event(event) virtual
Parameters

event (Gst.Event) –

Return type

bool

do_start() virtual
Return type

bool

do_stop() virtual
Return type

bool

do_submit_input_buffer(is_discont, input) virtual
Parameters
Return type

Gst.FlowReturn

do_transform(inbuf, outbuf) virtual
Parameters
Return type

Gst.FlowReturn

do_transform_caps(direction, caps, filter) virtual
Parameters
Return type

Gst.Caps

do_transform_ip(buf) virtual
Parameters

buf (Gst.Buffer) –

Return type

Gst.FlowReturn

do_transform_meta(outbuf, meta, inbuf) virtual
Parameters
Return type

bool

do_transform_size(direction, caps, size, othercaps) virtual
Parameters
Return type

(bool, othersize: int)

Property Details

GstBase.BaseTransform.props.qos
Name

qos

Type

bool

Default Value

False

Flags

READABLE, WRITABLE

Handle Quality-of-Service events