Struct gstreamer_base::Adapter

source ·

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

[trait@glib::ObjectExt]

GLib type: GObject with reference counted clone semantics.

Struct gstreamer_base::AdapterCopy item path

§Implements

Implementations§

impl Adapter

pub fn new() -> Adapter ⓘ

§Returns

pub fn available(&self) -> usize

§Returns

pub fn available_fast(&self) -> usize

§Returns

pub fn clear(&self)

pub fn distance_from_discont(&self) -> u64

§Returns

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

§Returns

pub fn offset_at_discont(&self) -> u64

§Returns

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

§Returns

§distance

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

§offset

§Returns

§distance

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

§Returns

§distance

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

§Returns

§distance

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

§offset

§Returns

§distance

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

§Returns

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>

§offset

§size

§Returns

pub fn flush(&self, flush: usize)

§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)

§buf

Trait Implementations§

impl Clone for Adapter

fn clone(&self) -> Self

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

impl Debug for Adapter

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

impl Default for Adapter

fn default() -> Self

impl HasParamSpec for Adapter

type ParamSpec = ParamSpecObject

type SetValue = Adapter

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,

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

impl Ord for Adapter

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

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

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

fn clamp(self, min: Self, max: Self) -> Selfwhere Self: Sized + PartialOrd,

impl ParentClassIs for Adapter

type Parent = Object

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

Struct gstreamer_base::Adapter

§`distance`

§`offset`

§`distance`

§`distance`

§`distance`

§`offset`

§`distance`

§`offset`

§`size`

§`flush`

§`buf`

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

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

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

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

fn clamp(self, min: Self, max: Self) -> Self
where Self: Sized + PartialOrd,

fn by_ref(&mut self) -> &mut Self
where Self: Sized,

fn bytes(self) -> Bytes<Self>
where Self: Sized,

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

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

impl<T> Any for T
where T: 'static + ?Sized,

impl<T> Borrow<T> for T
where T: ?Sized,

impl<T> BorrowMut<T> for T
where T: ?Sized,

impl<T> Cast for T
where T: ObjectType,

fn upcast<T>(self) -> T
where T: ObjectType, Self: IsA<T>,

fn upcast_ref<T>(&self) -> &T
where T: ObjectType, Self: IsA<T>,

fn downcast<T>(self) -> Result<T, Self>
where T: ObjectType, Self: MayDowncastTo<T>,

fn downcast_ref<T>(&self) -> Option<&T>
where T: ObjectType, Self: MayDowncastTo<T>,

fn dynamic_cast<T>(self) -> Result<T, Self>
where T: ObjectType,

fn dynamic_cast_ref<T>(&self) -> Option<&T>
where T: ObjectType,

unsafe fn unsafe_cast<T>(self) -> T
where T: ObjectType,

unsafe fn unsafe_cast_ref<T>(&self) -> &T
where T: ObjectType,

impl<T> CloneToUninit for T
where T: Clone,

impl<T> FromGlibContainerAsVec<<T as GlibPtrDefault>::GlibType, *const GList> for T
where T: GlibPtrDefault + FromGlibPtrNone<<T as GlibPtrDefault>::GlibType> + FromGlibPtrFull<<T as GlibPtrDefault>::GlibType>,

impl<T> FromGlibContainerAsVec<<T as GlibPtrDefault>::GlibType, *const GPtrArray> for T
where T: GlibPtrDefault + FromGlibPtrNone<<T as GlibPtrDefault>::GlibType> + FromGlibPtrFull<<T as GlibPtrDefault>::GlibType>,

impl<T> FromGlibContainerAsVec<<T as GlibPtrDefault>::GlibType, *const GSList> for T
where T: GlibPtrDefault + FromGlibPtrNone<<T as GlibPtrDefault>::GlibType> + FromGlibPtrFull<<T as GlibPtrDefault>::GlibType>,