Adapter

This class is for elements that receive buffers in an undesired size. While for example raw video contains one image per buffer, the same is not true for a lot of other formats, especially those that come directly from a file. So if you have undefined buffer sizes and require a specific size, this object is for you.

An adapter is created with gstbase.adapter.Adapter.new_. It can be freed again with gobject.object.ObjectG.unref.

The theory of operation is like this: All buffers received are put into the adapter using gstbase.adapter.Adapter.push and the data is then read back in chunks of the desired size using gstbase.adapter.Adapter.map/gstbase.adapter.Adapter.unmap and/or gstbase.adapter.Adapter.copy. After the data has been processed, it is freed using gstbase.adapter.Adapter.unmap.

Other methods such as gstbase.adapter.Adapter.take and gstbase.adapter.Adapter.takeBuffer combine gstbase.adapter.Adapter.map and gstbase.adapter.Adapter.unmap in one method and are potentially more convenient for some use cases.

For example, a sink pad's chain function that needs to pass data to a library in 512-byte chunks could be implemented like this:

static GstFlowReturn
sink_pad_chain (GstPad *pad, GstObject *parent, GstBuffer *buffer)
{
  MyElement *this;
  GstAdapter *adapter;
  GstFlowReturn ret = GST_FLOW_OK;

  this = MY_ELEMENT (parent);

  adapter = this->adapter;

  // put buffer into adapter
  gst_adapter_push (adapter, buffer);

  // while we can read out 512 bytes, process them
  while (gst_adapter_available (adapter) >= 512 && ret == GST_FLOW_OK) {
    const guint8 *data = gst_adapter_map (adapter, 512);
    // use flowreturn as an error value
    ret = my_library_foo (data);
    gst_adapter_unmap (adapter);
    gst_adapter_flush (adapter, 512);
  }
  return ret;
}

For another example, a simple element inside GStreamer that uses #GstAdapter is the libvisual element.

An element using #GstAdapter in its sink pad chain function should ensure that when the FLUSH_STOP event is received, that any queued data is cleared using gstbase.adapter.Adapter.clear. Data should also be cleared or processed on EOS and when changing state from gst.types.State.Paused to gst.types.State.Ready.

Also check the GST_BUFFER_FLAG_DISCONT flag on the buffer. Some elements might need to clear the adapter after a discontinuity.

The adapter will keep track of the timestamps of the buffers that were pushed. The last seen timestamp before the current position can be queried with gstbase.adapter.Adapter.prevPts. This function can optionally return the number of bytes between the start of the buffer that carried the timestamp and the current adapter position. The distance is useful when dealing with, for example, raw audio samples because it allows you to calculate the timestamp of the current adapter position by using the last seen timestamp and the amount of bytes since. Additionally, the gstbase.adapter.Adapter.prevPtsAtOffset can be used to determine the last seen timestamp at a particular offset in the adapter.

The adapter will also keep track of the offset of the buffers (#GST_BUFFER_OFFSET) that were pushed. The last seen offset before the current position can be queried with gstbase.adapter.Adapter.prevOffset. This function can optionally return the number of bytes between the start of the buffer that carried the offset and the current adapter position.

Additionally the adapter also keeps track of the PTS, DTS and buffer offset at the last discontinuity, which can be retrieved with gstbase.adapter.Adapter.ptsAtDiscont, gstbase.adapter.Adapter.dtsAtDiscont and gstbase.adapter.Adapter.offsetAtDiscont. The number of bytes that were consumed since then can be queried with gstbase.adapter.Adapter.distanceFromDiscont.

A last thing to note is that while #GstAdapter is pretty optimized, merging buffers still might be an operation that requires a malloc() and memcpy() operation, and these operations are not the fastest. Because of this, some functions like gstbase.adapter.Adapter.availableFast are provided to help speed up such cases should you want to. To avoid repeated memory allocations, gstbase.adapter.Adapter.copy can be used to copy data into a (statically allocated) user provided buffer.

#GstAdapter is not MT safe. All operations on an adapter must be serialized by the caller. This is not normally a problem, however, as the normal use case of #GstAdapter is inside one pad's chain function, in which case access is serialized via the pad's STREAM_LOCK.

Note that gstbase.adapter.Adapter.push takes ownership of the buffer passed. Use gst_buffer_ref() before pushing it into the adapter if you still want to access the buffer later. The adapter will never modify the data in the buffer pushed in it.

class Adapter : ObjectG {

this();

size_t available();

size_t availableFast();

void clear();

glib.bytes.Bytes copy(size_t offset, size_t size);

ulong distanceFromDiscont();

gst.types.ClockTime dtsAtDiscont();

void flush(size_t flush);

gst.buffer.Buffer getBuffer(size_t nbytes);

gst.buffer.Buffer getBufferFast(size_t nbytes);

gst.buffer_list.BufferList getBufferList(size_t nbytes);

gst.buffer.Buffer[] getList(size_t nbytes);

ptrdiff_t maskedScanUint32(uint mask, uint pattern, size_t offset, size_t size);

ptrdiff_t maskedScanUint32Peek(uint mask, uint pattern, size_t offset, size_t size, uint value);

ulong offsetAtDiscont();

gst.types.ClockTime prevDts(ulong distance);

gst.types.ClockTime prevDtsAtOffset(size_t offset, ulong distance);

ulong prevOffset(ulong distance);

gst.types.ClockTime prevPts(ulong distance);

gst.types.ClockTime prevPtsAtOffset(size_t offset, ulong distance);

gst.types.ClockTime ptsAtDiscont();

void push(gst.buffer.Buffer buf);

gst.buffer.Buffer takeBuffer(size_t nbytes);

gst.buffer.Buffer takeBufferFast(size_t nbytes);

gst.buffer_list.BufferList takeBufferList(size_t nbytes);

gst.buffer.Buffer[] takeList(size_t nbytes);

void unmap();

}

Constructors

this this(): Creates a new #GstAdapter. Free with gobject.object.ObjectG.unref.

Members

Functions

available size_t available(): Gets the maximum amount of bytes available, that is it returns the maximum value that can be supplied to gstbase.adapter.Adapter.map without that function returning null.
availableFast size_t availableFast(): Gets the maximum number of bytes that are immediately available without requiring any expensive operations (like copying the data into a temporary buffer).
clear void clear(): Removes all buffers from adapter.
copy glib.bytes.Bytes copy(size_t offset, size_t size): Similar to gst_adapter_copy, but more suitable for language bindings. size bytes of data starting at offset will be copied out of the buffers contained in adapter and into a new #GBytes structure which is returned. Depending on the value of the size argument an empty #GBytes structure may be returned.
distanceFromDiscont ulong distanceFromDiscont(): Get the distance in bytes since the last buffer with the gst.types.BufferFlags.Discont flag.
dtsAtDiscont gst.types.ClockTime dtsAtDiscont(): Get the DTS that was on the last buffer with the GST_BUFFER_FLAG_DISCONT flag, or GST_CLOCK_TIME_NONE.
flush void flush(size_t flush): Flushes the first flush bytes in the adapter. The caller must ensure that at least this many bytes are available.
getBuffer gst.buffer.Buffer getBuffer(size_t nbytes): Returns a #GstBuffer containing the first nbytes of the adapter, but does not flush them from the adapter. See gstbase.adapter.Adapter.takeBuffer for details.
getBufferFast gst.buffer.Buffer getBufferFast(size_t nbytes): Returns a #GstBuffer containing the first nbytes of the adapter, but does not flush them from the adapter. See gstbase.adapter.Adapter.takeBufferFast for details.
getBufferList gst.buffer_list.BufferList getBufferList(size_t nbytes): Returns a #GstBufferList of buffers containing the first nbytes bytes of the adapter but does not flush them from the adapter. See gstbase.adapter.Adapter.takeBufferList for details.
getList gst.buffer.Buffer[] getList(size_t nbytes): Returns a #GList of buffers containing the first nbytes bytes of the adapter, but does not flush them from the adapter. See gstbase.adapter.Adapter.takeList for details.
maskedScanUint32 ptrdiff_t maskedScanUint32(uint mask, uint pattern, size_t offset, size_t size): Scan for pattern pattern with applied mask mask in the adapter data, starting from offset offset.
maskedScanUint32Peek ptrdiff_t maskedScanUint32Peek(uint mask, uint pattern, size_t offset, size_t size, uint value): Scan for pattern pattern with applied mask mask in the adapter data, starting from offset offset. If a match is found, the value that matched is returned through value, otherwise value is left untouched.
offsetAtDiscont ulong offsetAtDiscont(): Get the offset that was on the last buffer with the GST_BUFFER_FLAG_DISCONT flag, or GST_BUFFER_OFFSET_NONE.
prevDts gst.types.ClockTime prevDts(ulong distance): Get the dts that was before the current byte in the adapter. When distance is given, the amount of bytes between the dts and the current position is returned.
prevDtsAtOffset gst.types.ClockTime prevDtsAtOffset(size_t offset, ulong distance): Get the dts that was before the byte at offset offset in the adapter. When distance is given, the amount of bytes between the dts and the current position is returned.
prevOffset ulong prevOffset(ulong distance): Get the offset that was before the current byte in the adapter. When distance is given, the amount of bytes between the offset and the current position is returned.
prevPts gst.types.ClockTime prevPts(ulong distance): Get the pts that was before the current byte in the adapter. When distance is given, the amount of bytes between the pts and the current position is returned.
prevPtsAtOffset gst.types.ClockTime prevPtsAtOffset(size_t offset, ulong distance): Get the pts that was before the byte at offset offset in the adapter. When distance is given, the amount of bytes between the pts and the current position is returned.
ptsAtDiscont gst.types.ClockTime ptsAtDiscont(): Get the PTS that was on the last buffer with the GST_BUFFER_FLAG_DISCONT flag, or GST_CLOCK_TIME_NONE.
push void push(gst.buffer.Buffer buf): Adds the data from buf to the data stored inside adapter and takes ownership of the buffer.
takeBuffer gst.buffer.Buffer takeBuffer(size_t nbytes): Returns a #GstBuffer containing the first nbytes bytes of the adapter. The returned bytes will be flushed from the adapter. This function is potentially more performant than gstbase.adapter.Adapter.take since it can reuse the memory in pushed buffers by subbuffering or merging. This function will always return a buffer with a single memory region.
takeBufferFast gst.buffer.Buffer takeBufferFast(size_t nbytes): Returns a #GstBuffer containing the first nbytes of the adapter. The returned bytes will be flushed from the adapter. This function is potentially more performant than gstbase.adapter.Adapter.takeBuffer since it can reuse the memory in pushed buffers by subbuffering or merging. Unlike gstbase.adapter.Adapter.takeBuffer, the returned buffer may be composed of multiple non-contiguous #GstMemory objects, no copies are made.
takeBufferList gst.buffer_list.BufferList takeBufferList(size_t nbytes): Returns a #GstBufferList of buffers containing the first nbytes bytes of the adapter. The returned bytes will be flushed from the adapter. When the caller can deal with individual buffers, this function is more performant because no memory should be copied.
takeList gst.buffer.Buffer[] takeList(size_t nbytes): Returns a #GList of buffers containing the first nbytes bytes of the adapter. The returned bytes will be flushed from the adapter. When the caller can deal with individual buffers, this function is more performant because no memory should be copied.
unmap void unmap(): Releases the memory obtained with the last gstbase.adapter.Adapter.map.

Inherited Members

From ObjectG

setGObject void setGObject(void* cObj, Flag!"Take" take): Set the GObject of a D ObjectG wrapper.
cPtr void* cPtr(Flag!"Dup" dup): Get a pointer to the underlying C object.
ref_ void* ref_(void* gObj): Calls g_object_ref() on a GObject.
unref unref(void* gObj): Calls g_object_unref() on a GObject.
getType GType getType(): Get the GType of an object.
gType GType gType [@property getter]: GObject GType property.
self ObjectG self(): Convenience method to return this cast to a type. For use in D with statements.
getDObject T getDObject(void* cptr, Flag!"Take" take): Template to get the D object from a C GObject and cast it to the given D object type.
connectSignalClosure ulong connectSignalClosure(string signalDetail, DClosure closure, Flag!"After" after): Connect a D closure to an object signal.
setProperty void setProperty(string propertyName, T val): Template for setting a GObject property.
getProperty T getProperty(string propertyName): Template for getting a GObject property.
compatControl size_t compatControl(size_t what, void* data)
bindProperty gobject.binding.Binding bindProperty(string sourceProperty, gobject.object.ObjectG target, string targetProperty, gobject.types.BindingFlags flags): Creates a binding between source_property on source and target_property on target.
bindPropertyFull gobject.binding.Binding bindPropertyFull(string sourceProperty, gobject.object.ObjectG target, string targetProperty, gobject.types.BindingFlags flags, gobject.closure.Closure transformTo, gobject.closure.Closure transformFrom): Creates a binding between source_property on source and target_property on target, allowing you to set the transformation functions to be used by the binding.
forceFloating void forceFloating(): This function is intended for #GObject implementations to re-enforce a floating[floating-ref] object reference. Doing this is seldom required: all #GInitiallyUnowneds are created with a floating reference which usually just needs to be sunken by calling gobject.object.ObjectG.refSink.
freezeNotify void freezeNotify(): Increases the freeze count on object. If the freeze count is non-zero, the emission of "notify" signals on object is stopped. The signals are queued until the freeze count is decreased to zero. Duplicate notifications are squashed so that at most one #GObject::notify signal is emitted for each property modified while the object is frozen.
getData void* getData(string key): Gets a named field from the objects table of associations (see gobject.object.ObjectG.setData).
getProperty void getProperty(string propertyName, gobject.value.Value value): Gets a property of an object.
getQdata void* getQdata(glib.types.Quark quark): This function gets back user data pointers stored via gobject.object.ObjectG.setQdata.
getv void getv(string[] names, gobject.value.Value[] values): Gets n_properties properties for an object. Obtained properties will be set to values. All properties must be valid. Warnings will be emitted and undefined behaviour may result if invalid properties are passed in.
isFloating bool isFloating(): Checks whether object has a floating[floating-ref] reference.
notify void notify(string propertyName): Emits a "notify" signal for the property property_name on object.
notifyByPspec void notifyByPspec(gobject.param_spec.ParamSpec pspec): Emits a "notify" signal for the property specified by pspec on object.
refSink gobject.object.ObjectG refSink(): Increase the reference count of object, and possibly remove the floating[floating-ref] reference, if object has a floating reference.
runDispose void runDispose(): Releases all references to other objects. This can be used to break reference cycles.
setData void setData(string key, void* data): Each object carries around a table of associations from strings to pointers. This function lets you set an association.
setProperty void setProperty(string propertyName, gobject.value.Value value): Sets a property on an object.
stealData void* stealData(string key): Remove a specified datum from the object's data associations, without invoking the association's destroy handler.
stealQdata void* stealQdata(glib.types.Quark quark): This function gets back user data pointers stored via gobject.object.ObjectG.setQdata and removes the data from object without invoking its destroy() function (if any was set). Usually, calling this function is only required to update user data pointers with a destroy notifier, for example:
thawNotify void thawNotify(): Reverts the effect of a previous call to gobject.object.ObjectG.freezeNotify. The freeze count is decreased on object and when it reaches zero, queued "notify" signals are emitted.
watchClosure void watchClosure(gobject.closure.Closure closure): This function essentially limits the life time of the closure to the life time of the object. That is, when the object is finalized, the closure is invalidated by calling gobject.closure.Closure.invalidate on it, in order to prevent invocations of the closure with a finalized (nonexisting) object. Also, gobject.object.ObjectG.ref_ and gobject.object.ObjectG.unref are added as marshal guards to the closure, to ensure that an extra reference count is held on object during invocation of the closure. Usually, this function will be called on closures that use this object as closure data.
connectNotify ulong connectNotify(string detail, T callback, Flag!"After" after): Connect to Notify signal.

gstbase adapter classes

Adapter