Struct gstreamer_base::Adapter

pub struct Adapter { /* private fields */ }

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

[trait@glib::ObjectExt]

GLib type: GObject with reference counted clone semantics.

Implementations

impl Adapter

pub fn new() -> Adapter

Creates a new Adapter. Free with g_object_unref().

Returns

a new Adapter

pub fn available(&self) -> usize

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

pub fn available_fast(&self) -> usize

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

pub fn clear(&self)

Removes all buffers from self.

pub fn distance_from_discont(&self) -> u64

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.

pub fn dts_at_discont(&self) -> Option<ClockTime>

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.

pub fn offset_at_discont(&self) -> u64

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.

pub fn prev_dts(&self) -> (Option<ClockTime>, u64)

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 added to 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

pub fn prev_dts_at_offset(&self, offset: usize) -> (Option<ClockTime>, u64)

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 added to 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

pub fn prev_offset(&self) -> (u64, u64)

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 added to 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

pub fn prev_pts(&self) -> (Option<ClockTime>, u64)

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 added to 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

pub fn prev_pts_at_offset(&self, offset: usize) -> (Option<ClockTime>, u64)

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 added to 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

pub fn pts_at_discont(&self) -> Option<ClockTime>

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.

impl Adapter

pub fn copy(&self, offset: usize, dest: &mut [u8]) -> Result<(), BoolError>

pub fn copy_bytes(&self, offset: usize, size: usize) -> Result<Bytes, BoolError>

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.

pub fn flush(&self, flush: usize)

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

pub fn buffer(&self, nbytes: usize) -> Result<Buffer, BoolError>

pub fn buffer_fast(&self, nbytes: usize) -> Result<Buffer, BoolError>

pub fn buffer_list(&self, nbytes: usize) -> Result<BufferList, BoolError>

pub fn list(&self, nbytes: usize) -> Result<Vec<Buffer>, BoolError>

pub fn masked_scan_uint32( &self, mask: u32, pattern: u32, offset: usize, size: usize, ) -> Result<Option<usize>, BoolError>

pub fn masked_scan_uint32_peek( &self, mask: u32, pattern: u32, offset: usize, size: usize, ) -> Result<Option<(usize, u32)>, BoolError>

pub fn take_buffer(&self, nbytes: usize) -> Result<Buffer, BoolError>

pub fn take_buffer_fast(&self, nbytes: usize) -> Result<Buffer, BoolError>

pub fn take_buffer_list(&self, nbytes: usize) -> Result<BufferList, BoolError>

pub fn take_list(&self, nbytes: usize) -> Result<Vec<Buffer>, BoolError>

pub fn push(&self, buf: Buffer)

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

impl Clone for Adapter

fn clone(&self) -> Self

Makes a clone of this shared reference.

This increments the strong reference count of the object. Dropping the object will decrement it again.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Adapter

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Adapter

fn default() -> Self

Returns the “default value” for a type.

impl HasParamSpec for Adapter

type ParamSpec = ParamSpecObject

type SetValue = Adapter

Preferred value to be used as setter for the associated ParamSpec.

type BuilderFn = fn(_: &str) -> ParamSpecObjectBuilder<'_, Adapter>

fn param_spec_builder() -> Self::BuilderFn

impl Hash for Adapter

fn hash<H>(&self, state: &mut H)

where H: Hasher,

Hashes the memory address of this object.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Ord for Adapter

fn cmp(&self, other: &Self) -> Ordering

Comparison for two GObjects.

Compares the memory addresses of the provided objects.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized + PartialOrd,

Restrict a value to a certain interval.

impl ParentClassIs for Adapter

type Parent = Object

impl<OT: ObjectType> PartialEq<OT> for Adapter

fn eq(&self, other: &OT) -> bool

Equality for two GObjects.

Two GObjects are equal if their memory addresses are equal.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<OT: ObjectType> PartialOrd<OT> for Adapter

fn partial_cmp(&self, other: &OT) -> Option<Ordering>

Partial comparison for two GObjects.

Compares the memory addresses of the provided objects.

fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl Read for Adapter

fn read(&mut self, buf: &mut [u8]) -> Result<usize, Error>

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

fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize, Error>

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

fn is_read_vectored(&self) -> bool

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

Determines if this Reader has an efficient read_vectored implementation.

fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize, Error>

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

fn read_to_string(&mut self, buf: &mut String) -> Result<usize, Error>

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

fn read_exact(&mut self, buf: &mut [u8]) -> Result<(), Error>

Reads the exact number of bytes required to fill buf.

fn read_buf(&mut self, buf: BorrowedCursor<'_>) -> Result<(), Error>

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

Pull some bytes from this source into the specified buffer.

fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<(), Error>

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

Reads the exact number of bytes required to fill cursor.

fn by_ref(&mut self) -> &mut Self

where Self: Sized,

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

fn bytes(self) -> Bytes<Self>

where Self: Sized,

Transforms this Read instance to an Iterator over its bytes.

fn chain<R>(self, next: R) -> Chain<Self, R>

where R: Read, Self: Sized,

Creates an adapter which will chain this stream with another.

fn take(self, limit: u64) -> Take<Self>

where Self: Sized,

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

impl StaticType for Adapter

fn static_type() -> Type

Returns the type identifier of Self.

impl Eq for Adapter