#[repr(transparent)]
pub struct Adapter { /* private fields */ }
Expand description

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 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 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:

⚠️ The following code is in C ⚠️

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 Adapter is the libvisual element.

An element using Adapter in its sink pad chain function should ensure that when the FLUSH_STOP event is received, that any queued data is cleared using 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 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 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 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 pts_at_discont(), dts_at_discont() and offset_at_discont(). The number of bytes that were consumed since then can be queried with distance_from_discont().

A last thing to note is that while Adapter 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 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.

Adapter 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 Adapter is inside one pad’s chain function, in which case access is serialized via the pad’s STREAM_LOCK.

Note that 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.

Implements

glib::ObjectExt

Implementations

Creates a new Adapter. Free with g_object_unref().

Returns

a new Adapter

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 None.

Returns

number of bytes available in self

Gets the maximum number of bytes that are immediately available without requiring any expensive operations (like copying the data into a temporary buffer).

Returns

number of bytes that are available in self without expensive operations

Removes all buffers from self.

This is supported on crate feature v1_10 only.

Get the distance in bytes since the last buffer with the gst::BufferFlags::DISCONT flag.

The distance will be reset to 0 for all buffers with gst::BufferFlags::DISCONT on them, and then calculated for all other following buffers based on their size.

Returns

The offset. Can be GST_BUFFER_OFFSET_NONE.

This is supported on crate feature v1_10 only.

Get the DTS that was on the last buffer with the GST_BUFFER_FLAG_DISCONT flag, or GST_CLOCK_TIME_NONE.

Returns

The DTS at the last discont or GST_CLOCK_TIME_NONE.

This is supported on crate feature v1_10 only.

Get the offset that was on the last buffer with the GST_BUFFER_FLAG_DISCONT flag, or GST_BUFFER_OFFSET_NONE.

Returns

The offset at the last discont or GST_BUFFER_OFFSET_NONE.

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.

The dts is reset to GST_CLOCK_TIME_NONE and the distance is set to 0 when the adapter is first created or when it is cleared. This also means that before the first byte with a dts is removed from the adapter, the dts and distance returned are GST_CLOCK_TIME_NONE and 0 respectively.

Returns

The previously seen dts.

distance

pointer to location for distance, or None

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.

The dts is reset to GST_CLOCK_TIME_NONE and the distance is set to 0 when the adapter is first created or when it is cleared. This also means that before the first byte with a dts is removed from the adapter, the dts and distance returned are GST_CLOCK_TIME_NONE and 0 respectively.

offset

the offset in the adapter at which to get timestamp

Returns

The previously seen dts at given offset.

distance

pointer to location for distance, or None

This is supported on crate feature v1_10 only.

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.

The offset is reset to GST_BUFFER_OFFSET_NONE and the distance is set to 0 when the adapter is first created or when it is cleared. This also means that before the first byte with an offset is removed from the adapter, the offset and distance returned are GST_BUFFER_OFFSET_NONE and 0 respectively.

Returns

The previous seen offset.

distance

pointer to a location for distance, or None

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.

The pts is reset to GST_CLOCK_TIME_NONE and the distance is set to 0 when the adapter is first created or when it is cleared. This also means that before the first byte with a pts is removed from the adapter, the pts and distance returned are GST_CLOCK_TIME_NONE and 0 respectively.

Returns

The previously seen pts.

distance

pointer to location for distance, or None

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.

The pts is reset to GST_CLOCK_TIME_NONE and the distance is set to 0 when the adapter is first created or when it is cleared. This also means that before the first byte with a pts is removed from the adapter, the pts and distance returned are GST_CLOCK_TIME_NONE and 0 respectively.

offset

the offset in the adapter at which to get timestamp

Returns

The previously seen pts at given offset.

distance

pointer to location for distance, or None

This is supported on crate feature v1_10 only.

Get the PTS that was on the last buffer with the GST_BUFFER_FLAG_DISCONT flag, or GST_CLOCK_TIME_NONE.

Returns

The PTS at the last discont or GST_CLOCK_TIME_NONE.

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 self and into a new glib::Bytes structure which is returned. Depending on the value of the size argument an empty glib::Bytes structure may be returned.

offset

the bytes offset in the adapter to start from

size

the number of bytes to copy

Returns

A new glib::Bytes structure containing the copied data.

Flushes the first flush bytes in the self. The caller must ensure that at least this many bytes are available.

See also: gst_adapter_map(), gst_adapter_unmap()

flush

the number of bytes to flush

Adds the data from buf to the data stored inside self and takes ownership of the buffer.

buf

a gst::Buffer to add to queue in the adapter

Trait Implementations

Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

Formats the value using the given formatter. Read more

Returns the “default value” for a type. Read more

Feeds this value into the given Hasher. Read more

Feeds a slice of this type into the given Hasher. Read more

This method returns an Ordering between self and other. Read more

Compares and returns the maximum of two values. Read more

Compares and returns the minimum of two values. Read more

Restrict a value to a certain interval. Read more

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

This method returns an ordering between self and other values if one exists. Read more

This method tests less than (for self and other) and is used by the < operator. Read more

This method tests less than or equal to (for self and other) and is used by the <= operator. Read more

This method tests greater than (for self and other) and is used by the > operator. Read more

This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more

Pull some bytes from this source into the specified buffer, returning how many bytes were read. Read more

Like read, except that it reads into a slice of buffers. Read more

🔬 This is a nightly-only experimental API. (can_vector)

Determines if this Reader has an efficient read_vectored implementation. Read more

Read all bytes until EOF in this source, placing them into buf. Read more

Read all bytes until EOF in this source, appending them to buf. Read more

Read the exact number of bytes required to fill buf. Read more

🔬 This is a nightly-only experimental API. (read_buf)

Pull some bytes from this source into the specified buffer. Read more

🔬 This is a nightly-only experimental API. (read_buf)

Read the exact number of bytes required to fill buf. Read more

Creates a “by reference” adaptor for this instance of Read. Read more

Transforms this Read instance to an Iterator over its bytes. Read more

Creates an adapter which will chain this stream with another. Read more

Creates an adapter which will read at most limit bytes from it. Read more

Returns the type identifier of Self.

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Upcasts an object to a superclass or interface T. Read more

Upcasts an object to a reference of its superclass or interface T. Read more

Tries to downcast to a subclass or interface implementor T. Read more

Tries to downcast to a reference of its subclass or interface implementor T. Read more

Tries to cast to an object of type T. This handles upcasting, downcasting and casting between interface and interface implementors. All checks are performed at runtime, while downcast and upcast will do many checks at compile-time already. Read more

Tries to cast to reference to an object of type T. This handles upcasting, downcasting and casting between interface and interface implementors. All checks are performed at runtime, while downcast and upcast will do many checks at compile-time already. Read more

Casts to T unconditionally. Read more

Casts to &T unconditionally. Read more

Performs the conversion.

Performs the conversion.

Returns true if the object is an instance of (can be cast to) T.

Returns the type of the object.

Returns the ObjectClass of the object. Read more

Returns the class of the object.

Returns the class of the object in the given type T. Read more

Returns the interface T of the object. Read more

Similar to Self::set_property but fails instead of panicking.

Sets the property property_name of the object to value value. Read more

Similar to Self::set_property but fails instead of panicking.

Sets the property property_name of the object to value value. Read more

Similar to Self::set_properties but fails instead of panicking.

Sets multiple properties of the object at once. Read more

Similar to Self::set_properties_from_value but fails instead of panicking.

Sets multiple properties of the object at once. Read more

Similar to Self::property but fails instead of panicking.

Gets the property property_name of the object and cast it to the type V. Read more

Similar to Self::property_value but fails instead of panicking.

Gets the property property_name of the object. Read more

Check if the object has a property property_name of the given type_. Read more

Get the type of the property property_name of this object. Read more

Get the ParamSpec of the property property_name of this object.

Return all ParamSpec of the properties of this object.

Freeze all property notifications until the return guard object is dropped. Read more

Set arbitrary data on this object with the given key. Read more

Return previously set arbitrary data of this object with the given key. Read more

Retrieve previously set arbitrary data of this object with the given key. Read more

Set arbitrary data on this object with the given key. Read more

Return previously set arbitrary data of this object with the given key. Read more

Retrieve previously set arbitrary data of this object with the given key. Read more

Block a given signal handler. Read more

Unblock a given signal handler.

Stop emission of the currently emitted signal.

Stop emission of the currently emitted signal by the (possibly detailed) signal name.

Similar to Self::connect but fails instead of panicking.

Connect to the signal signal_name on this object. Read more

Similar to Self::connect_id but fails instead of panicking.

Connect to the signal signal_id on this object. Read more

Similar to Self::connect_local but fails instead of panicking.

Connect to the signal signal_name on this object. Read more

Similar to Self::connect_local_id but fails instead of panicking.

Connect to the signal signal_id on this object. Read more

Similar to Self::connect_unsafe but fails instead of panicking.

Connect to the signal signal_name on this object. Read more

Similar to Self::connect_unsafe_id but fails instead of panicking.

Similar to Self::connect_closure but fails instead of panicking.

Connect a closure to the signal signal_name on this object. Read more

Similar to Self::connect_closure_id but fails instead of panicking.

Connect a closure to the signal signal_id on this object. Read more

Limits the lifetime of closure to the lifetime of the object. When the object’s reference count drops to zero, the closure will be invalidated. An invalidated closure will ignore any calls to Closure::invoke. Read more

Connect to the signal signal_id on this object. Read more

Similar to Self::emit but fails instead of panicking.

Emit signal by signal id. Read more

Similar to Self::emit_with_values but fails instead of panicking.

Same as Self::emit but takes Value for the arguments.

Similar to Self::emit_by_name but fails instead of panicking.

Emit signal by its name. Read more

Similar to Self::emit_by_name_with_values but fails instead of panicking.

Emit signal by its name. Read more

Similar to Self::emit_by_name_with_details but fails instead of panicking.

Emit signal by its name with details. Read more

Similar to Self::emit_by_name_with_details_and_values but fails instead of panicking.

Emit signal by its name with details. Read more

Similar to Self::emit_with_details but fails instead of panicking.

Emit signal by signal id with details. Read more

Similar to Self::emit_with_details_and_values but fails instead of panicking.

Emit signal by signal id with details. Read more

Disconnect a previously connected signal handler.

Connect to the notify signal of the object. Read more

Connect to the notify signal of the object. Read more

Connect to the notify signal of the object. Read more

Notify that the given property has changed its value. Read more

Notify that the given property has changed its value. Read more

Downgrade this object to a weak reference.

Bind property source_property on this object to the target_property on the target object. Read more

Returns the strong reference count of this object.

Ensures that the type has been registered with the type system.

The resulting type after obtaining ownership.

Creates owned data from borrowed data, usually by cloning. Read more

🔬 This is a nightly-only experimental API. (toowned_clone_into)

Uses borrowed data to replace owned data, usually by cloning. Read more

Returns a SendValue clone of self.

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.