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 gst_adapter_new(). It can be freed again with g_object_unref().

The theory of operation is like this: All buffers received are put into the adapter using gst_adapter_push() and the data is then read back in chunks of the desired size using gst_adapter_map()/gst_adapter_unmap() and/or gst_adapter_copy(). After the data has been processed, it is freed using gst_adapter_unmap().

Other methods such as gst_adapter_take() and gst_adapter_take_buffer() combine gst_adapter_map() and gst_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 gst_adapter_clear(). Data should also be cleared or processed on EOS and when changing state from %GST_STATE_PAUSED to %GST_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 gst_adapter_prev_pts(). 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 gst_adapter_prev_pts_at_offset() 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 gst_adapter_prev_offset(). 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 gst_adapter_pts_at_discont(), gst_adapter_dts_at_discont() and gst_adapter_offset_at_discont(). The number of bytes that were consumed since then can be queried with gst_adapter_distance_from_discont().

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 gst_adapter_available_fast() are provided to help speed up such cases should you want to. To avoid repeated memory allocations, gst_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 gst_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 {

protected

GstAdapter* gstAdapter;

GstAdapter* getAdapterStruct(bool transferOwnership);

void* getStruct();

this(GstAdapter* gstAdapter, bool ownedRef);

static GType getType();

this();

size_t available();

size_t availableFast();

void clear();

void copy(ubyte[] dest, size_t offset);

Bytes copyBytes(size_t offset, size_t size);

ulong distanceFromDiscont();

GstClockTime dtsAtDiscont();

void flush(size_t flush);

Buffer getBuffer(size_t nbytes);

Buffer getBufferFast(size_t nbytes);

BufferList getBufferList(size_t nbytes);

ListG getList(size_t nbytes);

ubyte[] map(size_t size);

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();

GstClockTime prevDts(ulong distance);

GstClockTime prevDtsAtOffset(size_t offset, ulong distance);

ulong prevOffset(ulong distance);

GstClockTime prevPts(ulong distance);

GstClockTime prevPtsAtOffset(size_t offset, ulong distance);

GstClockTime ptsAtDiscont();

void push(Buffer buf);

ubyte[] take(size_t nbytes);

Buffer takeBuffer(size_t nbytes);

Buffer takeBufferFast(size_t nbytes);

BufferList takeBufferList(size_t nbytes);

ListG takeList(size_t nbytes);

void unmap();

}

Constructors

this this(GstAdapter* gstAdapter, bool ownedRef): Sets our main struct and passes it to the parent class.
this this(): Creates a new #GstAdapter. Free with g_object_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 gst_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 void copy(ubyte[] dest, size_t offset): Copies @size bytes of data starting at @offset out of the buffers contained in #GstAdapter into an array @dest provided by the caller.
copyBytes Bytes copyBytes(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()
dtsAtDiscont GstClockTime 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.
getAdapterStruct GstAdapter* getAdapterStruct(bool transferOwnership): Get the main Gtk struct
getBuffer Buffer getBuffer(size_t nbytes): Returns a #GstBuffer containing the first @nbytes of the @adapter, but does not flush them from the adapter. See gst_adapter_take_buffer() for details.
getBufferFast Buffer getBufferFast(size_t nbytes): Returns a #GstBuffer containing the first @nbytes of the @adapter, but does not flush them from the adapter. See gst_adapter_take_buffer_fast() for details.
getBufferList 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 gst_adapter_take_buffer_list() for details.
getList ListG 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 gst_adapter_take_list() for details.
getStruct void* getStruct(): the main Gtk struct as a void*
map ubyte[] map(size_t size): Gets the first @size bytes stored in the @adapter. The returned pointer is valid until the next function is called on the adapter.
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 GstClockTime 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 GstClockTime 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 GstClockTime 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 GstClockTime 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 GstClockTime 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(Buffer buf): Adds the data from @buf to the data stored inside @adapter and takes ownership of the buffer.
take ubyte[] take(size_t nbytes): Returns a freshly allocated buffer containing the first @nbytes bytes of the @adapter. The returned bytes will be flushed from the adapter.
takeBuffer 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 gst_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 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 gst_adapter_take_buffer() since it can reuse the memory in pushed buffers by subbuffering or merging. Unlike gst_adapter_take_buffer(), the returned buffer may be composed of multiple non-contiguous #GstMemory objects, no copies are made.
takeBufferList 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 ListG 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 gst_adapter_map().

Static functions

getType GType getType()

Variables

gstAdapter GstAdapter* gstAdapter;: the main Gtk struct

Inherited Members

From ObjectG

gObject GObject* gObject;: the main Gtk struct
ownedRef bool ownedRef;: Undocumented in source.
getObjectGStruct GObject* getObjectGStruct(bool transferOwnership): Get the main Gtk struct
getStruct void* getStruct(): the main Gtk struct as a void*
isGcRoot bool isGcRoot;: Undocumented in source.
signals DClosure[gulong] signals;: Undocumented in source.
destroyNotify void destroyNotify(ObjectG obj): Undocumented in source. Be warned that the author may not have intended to support it.
toggleNotify void toggleNotify(ObjectG obj, GObject* object, int isLastRef): Undocumented in source. Be warned that the author may not have intended to support it.
~this ~this(): Undocumented in source.
opCast T opCast()
getDObject RT getDObject(U obj, bool ownedRef): Gets a D Object from the objects table of associations.
removeGcRoot void removeGcRoot(): Undocumented in source. Be warned that the author may not have intended to support it.
setProperty void setProperty(string propertyName, T value)
unref deprecated void unref(ObjectG obj): Undocumented in source. Be warned that the author may not have intended to support it.
doref deprecated ObjectG doref(ObjectG obj): Undocumented in source. Be warned that the author may not have intended to support it.
addOnNotify gulong addOnNotify(void delegate(ParamSpec, ObjectG) dlg, string property, ConnectFlags connectFlags): The notify signal is emitted on an object when one of its properties has been changed. Note that getting this signal doesn't guarantee that the value of the property has actually changed, it may also be emitted when the setter for the property is called to reinstate the previous value.
getType GType getType()
compatControl size_t compatControl(size_t what, void* data)
interfaceFindProperty ParamSpec interfaceFindProperty(TypeInterface gIface, string propertyName): Find the #GParamSpec with the given name for an interface. Generally, the interface vtable passed in as @g_iface will be the default vtable from g_type_default_interface_ref(), or, if you know the interface has already been loaded, g_type_default_interface_peek().
interfaceInstallProperty void interfaceInstallProperty(TypeInterface gIface, ParamSpec pspec): Add a property to an interface; this is only useful for interfaces that are added to GObject-derived types. Adding a property to an interface forces all objects classes with that interface to have a compatible property. The compatible property could be a newly created #GParamSpec, but normally g_object_class_override_property() will be used so that the object class only needs to provide an implementation and inherits the property description, default value, bounds, and so forth from the interface property.
interfaceListProperties ParamSpec[] interfaceListProperties(TypeInterface gIface): Lists the properties of an interface.Generally, the interface vtable passed in as @g_iface will be the default vtable from g_type_default_interface_ref(), or, if you know the interface has already been loaded, g_type_default_interface_peek().
addToggleRef void addToggleRef(GToggleNotify notify, void* data): Increases the reference count of the object by one and sets a callback to be called when all other references to the object are dropped, or when this is already the last reference to the object and another reference is established.
addWeakPointer void addWeakPointer(void* weakPointerLocation): Adds a weak reference from weak_pointer to @object to indicate that the pointer located at @weak_pointer_location is only valid during the lifetime of @object. When the @object is finalized, @weak_pointer will be set to %NULL.
bindProperty Binding bindProperty(string sourceProperty, ObjectG target, string targetProperty, GBindingFlags flags): Creates a binding between @source_property on @source and @target_property on @target. Whenever the @source_property is changed the @target_property is updated using the same value. For instance:
bindPropertyFull Binding bindPropertyFull(string sourceProperty, ObjectG target, string targetProperty, GBindingFlags flags, GBindingTransformFunc transformTo, GBindingTransformFunc transformFrom, void* userData, GDestroyNotify notify): Complete version of g_object_bind_property().
bindPropertyWithClosures Binding bindPropertyWithClosures(string sourceProperty, ObjectG target, string targetProperty, GBindingFlags flags, Closure transformTo, 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.
dupData void* dupData(string key, GDuplicateFunc dupFunc, void* userData): This is a variant of g_object_get_data() which returns a 'duplicate' of the value. @dup_func defines the meaning of 'duplicate' in this context, it could e.g. take a reference on a ref-counted object.
dupQdata void* dupQdata(GQuark quark, GDuplicateFunc dupFunc, void* userData): This is a variant of g_object_get_qdata() which returns a 'duplicate' of the value. @dup_func defines the meaning of 'duplicate' in this context, it could e.g. take a reference on a ref-counted object.
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 g_object_ref_sink().
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 g_object_set_data()).
getProperty void getProperty(string propertyName, Value value): Gets a property of an object.
getQdata void* getQdata(GQuark quark): This function gets back user data pointers stored via g_object_set_qdata().
getValist void getValist(string firstPropertyName, void* varArgs): Gets properties of an object.
getv void getv(string[] names, 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(ParamSpec pspec): Emits a "notify" signal for the property specified by @pspec on @object.
doref alias doref = ref_: Undocumented in source.
ref_ ObjectG ref_(): Increases the reference count of @object.
refSink ObjectG refSink(): Increase the reference count of @object, and possibly remove the floating[floating-ref] reference, if @object has a floating reference.
removeToggleRef void removeToggleRef(GToggleNotify notify, void* data): Removes a reference added with g_object_add_toggle_ref(). The reference count of the object is decreased by one.
removeWeakPointer void removeWeakPointer(void* weakPointerLocation): Removes a weak reference from @object that was previously added using g_object_add_weak_pointer(). The @weak_pointer_location has to match the one used with g_object_add_weak_pointer().
replaceData bool replaceData(string key, void* oldval, void* newval, GDestroyNotify destroy, GDestroyNotify oldDestroy): Compares the user data for the key @key on @object with @oldval, and if they are the same, replaces @oldval with @newval.
replaceQdata bool replaceQdata(GQuark quark, void* oldval, void* newval, GDestroyNotify destroy, GDestroyNotify oldDestroy): Compares the user data for the key @quark on @object with @oldval, and if they are the same, replaces @oldval with @newval.
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.
setDataFull void setDataFull(string key, void* data, GDestroyNotify destroy): Like g_object_set_data() except it adds notification for when the association is destroyed, either by setting it to a different value or when the object is destroyed.
setProperty void setProperty(string propertyName, Value value): Sets a property on an object.
setQdata void setQdata(GQuark quark, void* data): This sets an opaque, named pointer on an object. The name is specified through a #GQuark (retrived e.g. via g_quark_from_static_string()), and the pointer can be gotten back from the @object with g_object_get_qdata() until the @object is finalized. Setting a previously set user data pointer, overrides (frees) the old pointer set, using #NULL as pointer essentially removes the data stored.
setQdataFull void setQdataFull(GQuark quark, void* data, GDestroyNotify destroy): This function works like g_object_set_qdata(), but in addition, a void (*destroy) (gpointer) function may be specified which is called with @data as argument when the @object is finalized, or the data is being overwritten by a call to g_object_set_qdata() with the same @quark.
setValist void setValist(string firstPropertyName, void* varArgs): Sets properties on an object.
setv void setv(string[] names, Value[] values): Sets @n_properties properties for an @object. Properties to be set will be taken from @values. All properties must be valid. Warnings will be emitted and undefined behaviour may result if invalid properties are passed in.
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(GQuark quark): This function gets back user data pointers stored via g_object_set_qdata() 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: |[ void object_add_to_user_list (GObject *object, const gchar *new_string) { // the quark, naming the object data GQuark quark_string_list = g_quark_from_static_string ("my-string-list"); // retrive the old string list GList *list = g_object_steal_qdata (object, quark_string_list);
thawNotify void thawNotify(): Reverts the effect of a previous call to g_object_freeze_notify(). The freeze count is decreased on @object and when it reaches zero, queued "notify" signals are emitted.
unref void unref(): Decreases the reference count of @object. When its reference count drops to 0, the object is finalized (i.e. its memory is freed).
watchClosure void watchClosure(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 g_closure_invalidate() on it, in order to prevent invocations of the closure with a finalized (nonexisting) object. Also, g_object_ref() and g_object_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.
weakRef void weakRef(GWeakNotify notify, void* data): Adds a weak reference callback to an object. Weak references are used for notification when an object is finalized. They are called "weak references" because they allow you to safely hold a pointer to an object without calling g_object_ref() (g_object_ref() adds a strong reference, that is, forces the object to stay alive).
weakUnref void weakUnref(GWeakNotify notify, void* data): Removes a weak reference callback to an object.
clearObject void clearObject(ObjectG objectPtr): Clears a reference to a #GObject.