BaseTransform

class BaseTransform(**properties: Any)

Superclasses: Element, Object, InitiallyUnowned, Object

Constructors:

BaseTransform(**properties)

Methods

class BaseTransform

get_allocator() → tuple[Allocator, AllocationParams]

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

Unref the allocator after use.

get_buffer_pool() → BufferPool | None

is_in_place() → bool

See if trans is configured as a in_place transform.

is_passthrough() → bool

See if trans is configured as a passthrough transform.

is_qos_enabled() → bool

Queries if the transform will handle QoS.

reconfigure() → bool

Negotiates src pad caps with downstream elements if the source pad is marked as needing reconfiguring. Unmarks GST_PAD_FLAG_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.

Added in version 1.18.

reconfigure_sink() → None

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

reconfigure_src() → None

Instructs trans 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: bool) → None

If gap_aware is False (the default), output buffers will have the %GST_BUFFER_FLAG_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.

Parameters:

gap_aware – New state

set_in_place(in_place: bool) → None

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.

Parameters:

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

set_passthrough(passthrough: bool) → None

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.

Parameters:

passthrough – boolean indicating passthrough mode.

set_prefer_passthrough(prefer_passthrough: bool) → None

If prefer_passthrough is True (the default), trans 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.

Added in version 1.0.1.

Parameters:

prefer_passthrough – New state

set_qos_enabled(enabled: bool) → None

Enable or disable QoS handling in the transform.

MT safe.

Parameters:

enabled – new state

update_qos(proportion: float, diff: int, timestamp: int) → None

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.

Parameters:

• proportion – the proportion

• diff – the diff against the clock

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

update_src_caps(updated_caps: Caps) → 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.

Added in version 1.6.

Parameters:

updated_caps – An updated version of the srcpad caps to be pushed downstream

Properties

class BaseTransform

props.qos: bool

Virtual Methods

class BaseTransform

do_accept_caps(direction: PadDirection, caps: Caps) → bool

Optional. Subclasses can override this method to check if caps can be handled by the element. The default implementation might not be the most optimal way to check this in all cases.

Parameters:

• direction

• caps

do_before_transform(buffer: Buffer) → None

Optional. This method is called right before the base class will start processing. Dynamic properties or other delayed configuration could be performed in this method.

Parameters:

buffer

do_copy_metadata(input: Buffer, outbuf: Buffer) → bool

Optional. Copy the metadata from the input buffer to the output buffer. The default implementation will copy the flags, timestamps and offsets of the buffer.

Parameters:

• input

• outbuf

do_decide_allocation(query: Query) → bool

Setup the allocation parameters for allocating output buffers. The passed in query contains the result of the downstream allocation query. This function is only called when not operating in passthrough mode. The default implementation will remove all memory dependent metadata. If there is a filter_meta method implementation, it will be called for all metadata API in the downstream query, otherwise the metadata API is removed.

Parameters:

query

do_filter_meta(query: Query, api: type, params: Structure) → bool

Return True if the metadata API should be proposed in the upstream allocation query. The default implementation is None and will cause all metadata to be removed.

Parameters:

• query

• api

• params

do_fixate_caps(direction: PadDirection, caps: Caps, othercaps: Caps) → Caps

Parameters:

• direction

• caps

• othercaps

do_generate_output() → tuple[FlowReturn, Buffer]

do_get_unit_size(caps: Caps) → tuple[bool, int]

Parameters:

caps

do_prepare_output_buffer(input: Buffer) → tuple[FlowReturn, Buffer]

Parameters:

input

do_propose_allocation(decide_query: Query, query: Query) → bool

Propose buffer allocation parameters for upstream elements. This function must be implemented if the element reads or writes the buffer content. The query that was passed to the decide_allocation is passed in this method (or None when the element is in passthrough mode). The default implementation will pass the query downstream when in passthrough mode and will copy all the filtered metadata API in non-passthrough mode.

Parameters:

• decide_query

• query

do_query(direction: PadDirection, query: Query) → bool

Optional. Handle a requested query. Subclasses that implement this must chain up to the parent if they didn’t handle the query

Parameters:

• direction

• query

do_set_caps(incaps: Caps, outcaps: Caps) → bool

Allows the subclass to be notified of the actual caps set.

Parameters:

• incaps

• outcaps

do_sink_event(event: Event) → bool

Parameters:

event

do_src_event(event: Event) → bool

Parameters:

event

do_start() → bool

Optional. Called when the element starts processing. Allows opening external resources.

do_stop() → bool

Optional. Called when the element stops processing. Allows closing external resources.

do_submit_input_buffer(is_discont: bool, input: Buffer) → FlowReturn

Function which accepts a new input buffer and pre-processes it. The default implementation performs caps (re)negotiation, then QoS if needed, and places the input buffer into the queued_buf member variable. If the buffer is dropped due to QoS, it returns GST_BASE_TRANSFORM_FLOW_DROPPED. If this input buffer is not contiguous with any previous input buffer, then is_discont is set to True. (Since: 1.6)

Parameters:

• is_discont

• input

do_transform(inbuf: Buffer, outbuf: Buffer) → FlowReturn

Required if the element does not operate in-place. Transforms one incoming buffer to one outgoing buffer. The function is allowed to change size/timestamp/duration of the outgoing buffer.

Parameters:

• inbuf

• outbuf

do_transform_caps(direction: PadDirection, caps: Caps, filter: Caps) → Caps

Optional. Given the pad in this direction and the given caps, what caps are allowed on the other pad in this element ?

Parameters:

• direction

• caps

• filter

do_transform_ip(buf: Buffer) → FlowReturn

Required if the element operates in-place. Transform the incoming buffer in-place.

Parameters:

buf

do_transform_meta(outbuf: Buffer, meta: Meta, inbuf: Buffer) → bool

Optional. Transform the metadata on the input buffer to the output buffer. By default this method copies all meta without tags. Subclasses can implement this method and return True if the metadata is to be copied.

Parameters:

• outbuf

• meta

• inbuf

do_transform_size(direction: PadDirection, caps: Caps, size: int, othercaps: Caps) → tuple[bool, int]

Parameters:

• direction

• caps

• size

• othercaps

Fields

class BaseTransform

element

have_segment

priv

queued_buf

segment

sinkpad

srcpad