Class BaseTransform

java.lang.Object
org.javagi.base.ProxyInstance
org.gnome.gobject.TypeInstance
org.gnome.gobject.GObject
org.gnome.gobject.InitiallyUnowned
org.freedesktop.gstreamer.gst.GstObject
org.freedesktop.gstreamer.gst.Element
org.freedesktop.gstreamer.base.BaseTransform
All Implemented Interfaces:
Proxy
Direct Known Subclasses:
AudioFilter, BaseTransform.BaseTransform$Impl, VideoFilter
@Generated("org.javagi.JavaGI") public abstract class BaseTransform extends Element

This base class is for filter elements that process data. Elements that are suitable for implementation using GstBaseTransform 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 GstBaseTransformClass.passthrough_on_same_caps variable will automatically set/unset passthrough based on whether the element negotiates the same caps on both pads.

  • GstBaseTransformClass.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 GstBaseTransform

  • 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.

  • Constructor Details

    • BaseTransform

      public BaseTransform(MemorySegment address)
      Create a BaseTransform instance for the provided memory address.
      Parameters:
      address - the memory address of the native object

    • BaseTransform

      public BaseTransform()
      Create a new BaseTransform.

  • Method Details

    • getType

      public static @Nullable Type getType()
      Get the GType of the BaseTransform class.
      Returns:
      the GType

    • getMemoryLayout

      public static MemoryLayout getMemoryLayout()
      The memory layout of the native struct.
      Returns:
      the memory layout

    • asParent

      protected BaseTransform asParent()
      Return this instance as if it were its parent type. Comparable to the Java super keyword, but ensures the parent typeclass is also used in native code.
      Overrides:
      asParent in class Element
      Returns:
      the instance as if it were its parent type

    • getAllocator

      public void getAllocator(@Nullable Out<Allocator> allocator, @Nullable AllocationParams params)

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

      Unref the allocator after use.

      Parameters:
      allocator - the GstAllocator used
      params - the GstAllocationParams of allocator

    • getBufferPool

      public @Nullable BufferPool getBufferPool()

    • isInPlace

      public boolean isInPlace()
      See if this BaseTransform is configured as a in_place transform.
      Returns:

      true if the transform is configured in in_place mode.

      MT safe.

    • isPassthrough

      public boolean isPassthrough()
      See if this BaseTransform is configured as a passthrough transform.
      Returns:

      true if the transform is configured in passthrough mode.

      MT safe.

    • isQosEnabled

      public boolean isQosEnabled()
      Queries if the transform will handle QoS.
      Returns:

      true if QoS is enabled.

      MT safe.

    • reconfigure

      public boolean reconfigure()

      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.

      Returns:
      true if the negotiation succeeded, else false.
      Since:
      1.18

    • reconfigureSink

      public void reconfigureSink()
      Instructs this BaseTransform to request renegotiation upstream. This function is typically called after properties on the transform were set that influence the input format.

    • reconfigureSrc

      public void reconfigureSrc()
      Instructs this BaseTransform 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.

    • setGapAware

      public void setGapAware(boolean gapAware)

      If gapAware is false (the default), output buffers will have the 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.

      Parameters:
      gapAware - New state

    • setInPlace

      public void setInPlace(boolean inPlace)

      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:
      inPlace - Boolean value indicating that we would like to operate on in_place buffers.

    • setPassthrough

      public void setPassthrough(boolean passthrough)

      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.

    • setPreferPassthrough

      public void setPreferPassthrough(boolean preferPassthrough)

      If preferPassthrough is true (the default), this BaseTransform 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.

      Parameters:
      preferPassthrough - New state
      Since:
      1.0.1

    • setQosEnabled

      public void setQosEnabled(boolean enabled)

      Enable or disable QoS handling in the transform.

      MT safe.

      Parameters:
      enabled - new state

    • updateQos

      public void updateQos(double proportion, ClockTimeDiff diff, ClockTime timestamp)

      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.

    • updateSrcCaps

      public boolean updateSrcCaps(Caps updatedCaps)
      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.
      Parameters:
      updatedCaps - An updated version of the srcpad caps to be pushed downstream
      Returns:
      true if the caps could be sent downstream false otherwise
      Since:
      1.6

    • acceptCaps

      protected boolean acceptCaps(PadDirection direction, Caps caps)
      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.

    • beforeTransform

      protected void beforeTransform(Buffer buffer)
      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.

    • copyMetadata

      protected boolean copyMetadata(Buffer input, Buffer outbuf)
      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.

    • decideAllocation

      protected boolean decideAllocation(Query query)
      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 filterMeta method implementation, it will be called for all metadata API in the downstream query, otherwise the metadata API is removed.

    • filterMeta

      protected boolean filterMeta(Query query, Type api, Structure params)
      Return true if the metadata API should be proposed in the upstream allocation query. The default implementation is null and will cause all metadata to be removed.

    • fixateCaps

      protected Caps fixateCaps(PadDirection direction, Caps caps, Caps othercaps)

    • generateOutput

      protected FlowReturn generateOutput(Out<Buffer> outbuf)

    • getUnitSize

      protected boolean getUnitSize(Caps caps, Out<Long> size)

    • prepareOutputBuffer

      protected FlowReturn prepareOutputBuffer(Buffer input, Out<Buffer> outbuf)

    • proposeAllocation

      protected boolean proposeAllocation(Query decideQuery, Query query)
      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 null 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.

    • query

      protected boolean query(PadDirection direction, Query query)
      Optional. Handle a requested query. Subclasses that implement this must chain up to the parent if they didn't handle the query

    • setCaps

      protected boolean setCaps(Caps incaps, Caps outcaps)
      Allows the subclass to be notified of the actual caps set.

    • sinkEvent

      protected boolean sinkEvent(Event event)

    • srcEvent

      protected boolean srcEvent(Event event)

    • start

      protected boolean start()
      Optional. Called when the element starts processing. Allows opening external resources.

    • stop

      protected boolean stop()
      Optional. Called when the element stops processing. Allows closing external resources.

    • submitInputBuffer

      protected FlowReturn submitInputBuffer(boolean isDiscont, Buffer input)
      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 queuedBuf 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 isDiscont is set to true. (Since: 1.6)

    • transform

      protected FlowReturn transform(Buffer inbuf, Buffer outbuf)
      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.

    • transformCaps

      protected Caps transformCaps(PadDirection direction, Caps caps, Caps filter)
      Optional. Given the pad in this direction and the given caps, what caps are allowed on the other pad in this element ?

    • transformIp

      protected FlowReturn transformIp(Buffer buf)
      Required if the element operates in-place. Transform the incoming buffer in-place.

    • transformMeta

      protected boolean transformMeta(Buffer outbuf, Meta meta, Buffer inbuf)
      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.

    • transformSize

      protected boolean transformSize(PadDirection direction, Caps caps, long size, Caps othercaps, Out<Long> othersize)