GI.GstBase.Objects.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 adapterNew. It can be freed again with objectUnref.

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

Other methods such as adapterTake and adapterTakeBuffer combine adapterMap and adapterUnmap 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:

C code

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 adapterClear. Data should also be cleared or processed on EOS and when changing state from StatePaused to StateReady.

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 adapterPrevPts. 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 adapterPrevPtsAtOffset 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 adapterPrevOffset. 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 adapterPtsAtDiscont, adapterDtsAtDiscont and adapterOffsetAtDiscont. The number of bytes that were consumed since then can be queried with adapterDistanceFromDiscont.

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 adapterAvailableFast 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 adapterPush 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.

Exported types

newtype Adapter

Memory-managed wrapper type.

Constructors

Adapter (ManagedPtr Adapter)

Instances

Eq Adapter

Defined in GI.GstBase.Objects.Adapter

Methods

(==) :: Adapter -> Adapter -> Bool

(/=) :: Adapter -> Adapter -> Bool

GObject Adapter

Defined in GI.GstBase.Objects.Adapter

ManagedPtrNewtype Adapter

Defined in GI.GstBase.Objects.Adapter

Methods

toManagedPtr :: Adapter -> ManagedPtr Adapter

TypedObject Adapter

Defined in GI.GstBase.Objects.Adapter

Methods

glibType :: IO GType

HasParentTypes Adapter

Defined in GI.GstBase.Objects.Adapter

IsGValue (Maybe Adapter)

Convert Adapter to and from GValue. See toGValue and fromGValue.

Defined in GI.GstBase.Objects.Adapter

Methods

gvalueGType_ :: IO GType

gvalueSet_ :: Ptr GValue -> Maybe Adapter -> IO ()

gvalueGet_ :: Ptr GValue -> IO (Maybe Adapter)

type ParentTypes Adapter

Defined in GI.GstBase.Objects.Adapter

type ParentTypes Adapter = '[Object]

class (GObject o, IsDescendantOf Adapter o) => IsAdapter o

Type class for types which can be safely cast to Adapter, for instance with toAdapter.

Instances

(GObject o, IsDescendantOf Adapter o) => IsAdapter o

Defined in GI.GstBase.Objects.Adapter

toAdapter :: (MonadIO m, IsAdapter o) => o -> m Adapter

Cast to Adapter, for types for which this is known to be safe. For general casts, use castTo.

Methods

Click to display all available methods, including inherited ones

Methods

available, availableFast, bindProperty, bindPropertyFull, clear, copy, distanceFromDiscont, dtsAtDiscont, flush, forceFloating, freezeNotify, getv, isFloating, map, maskedScanUint32, maskedScanUint32Peek, notify, notifyByPspec, offsetAtDiscont, prevDts, prevDtsAtOffset, prevOffset, prevPts, prevPtsAtOffset, ptsAtDiscont, push, ref, refSink, runDispose, stealData, stealQdata, take, takeBuffer, takeBufferFast, takeBufferList, takeList, thawNotify, unmap, unref, watchClosure.

Getters

getBuffer, getBufferFast, getBufferList, getData, getList, getProperty, getQdata.

Setters

setData, setDataFull, setProperty.

available

adapterAvailable

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> m Word64

Returns: number of bytes available in adapter

Gets the maximum amount of bytes available, that is it returns the maximum value that can be supplied to adapterMap without that function returning Nothing.

availableFast

adapterAvailableFast

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> m Word64

Returns: number of bytes that are available in adapter without expensive operations

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

clear

adapterClear

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> m ()

Removes all buffers from adapter.

copy

adapterCopy

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> Word64

offset: the bytes offset in the adapter to start from

-> Word64

size: the number of bytes to copy

-> m Bytes

Returns: A new Bytes structure containing the copied data.

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 Bytes structure which is returned. Depending on the value of the size argument an empty Bytes structure may be returned.

Since: 1.4

distanceFromDiscont

adapterDistanceFromDiscont

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> m Word64

Returns: The offset. Can be BUFFER_OFFSET_NONE.

Get the distance in bytes since the last buffer with the BufferFlagsDiscont flag.

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

Since: 1.10

dtsAtDiscont

adapterDtsAtDiscont

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> m Word64

Returns: The DTS at the last discont or GST_CLOCK_TIME_NONE.

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

Since: 1.10

flush

adapterFlush

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> Word64

flush: the number of bytes to flush

-> m ()

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

See also: adapterMap, adapterUnmap

getBuffer

adapterGetBuffer

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> Word64

nbytes: the number of bytes to get

-> m (Maybe Buffer)

Returns: a Buffer containing the first nbytes of the adapter, or Nothing if nbytes bytes are not available. gst_buffer_unref() when no longer needed.

Returns a Buffer containing the first nbytes of the adapter, but does not flush them from the adapter. See adapterTakeBuffer for details.

Caller owns a reference to the returned buffer. gst_buffer_unref() after usage.

Free-function: gst_buffer_unref

Since: 1.6

getBufferFast

adapterGetBufferFast

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> Word64

nbytes: the number of bytes to get

-> m (Maybe Buffer)

Returns: a Buffer containing the first nbytes of the adapter, or Nothing if nbytes bytes are not available. gst_buffer_unref() when no longer needed.

Returns a Buffer containing the first nbytes of the adapter, but does not flush them from the adapter. See adapterTakeBufferFast for details.

Caller owns a reference to the returned buffer. gst_buffer_unref() after usage.

Free-function: gst_buffer_unref

Since: 1.6

getBufferList

adapterGetBufferList

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> Word64

nbytes: the number of bytes to get

-> m (Maybe BufferList)

Returns: a BufferList of buffers containing the first nbytes of the adapter, or Nothing if nbytes bytes are not available

Returns a BufferList of buffers containing the first nbytes bytes of the adapter but does not flush them from the adapter. See adapterTakeBufferList for details.

Caller owns the returned list. Call gst_buffer_list_unref() to free the list after usage.

Since: 1.6

getList

adapterGetList

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> Word64

nbytes: the number of bytes to get

-> m [Buffer]

Returns: a List of buffers containing the first nbytes of the adapter, or Nothing if nbytes bytes are not available

Returns a List of buffers containing the first nbytes bytes of the adapter, but does not flush them from the adapter. See adapterTakeList for details.

Caller owns returned list and contained buffers. gst_buffer_unref() each buffer in the list before freeing the list after usage.

Since: 1.6

map

adapterMap

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> m (Maybe ByteString)

Returns: a pointer to the first size bytes of data, or Nothing

Gets the first size bytes stored in the adapter. The returned pointer is valid until the next function is called on the adapter.

Note that setting the returned pointer as the data of a Buffer is incorrect for general-purpose plugins. The reason is that if a downstream element stores the buffer so that it has access to it outside of the bounds of its chain function, the buffer will have an invalid data pointer after your element flushes the bytes. In that case you should use adapterTake, which returns a freshly-allocated buffer that you can set as Buffer memory or the potentially more performant adapterTakeBuffer.

Returns Nothing if size bytes are not available.

maskedScanUint32

adapterMaskedScanUint32

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> Word32

mask: mask to apply to data before matching against pattern

-> Word32

pattern: pattern to match (after mask is applied)

-> Word64

offset: offset into the adapter data from which to start scanning, returns the last scanned position.

-> Word64

size: number of bytes to scan from offset

-> m Int64

Returns: offset of the first match, or -1 if no match was found.

Example: > >// Assume the adapter contains 0x00 0x01 0x02 ... 0xfe 0xff > >gst_adapter_masked_scan_uint32 (adapter, 0xffffffff, 0x00010203, 0, 256); >// -> returns 0 >gst_adapter_masked_scan_uint32 (adapter, 0xffffffff, 0x00010203, 1, 255); >// -> returns -1 >gst_adapter_masked_scan_uint32 (adapter, 0xffffffff, 0x01020304, 1, 255); >// -> returns 1 >gst_adapter_masked_scan_uint32 (adapter, 0xffff, 0x0001, 0, 256); >// -> returns -1 >gst_adapter_masked_scan_uint32 (adapter, 0xffff, 0x0203, 0, 256); >// -> returns 0 >gst_adapter_masked_scan_uint32 (adapter, 0xffff0000, 0x02030000, 0, 256); >// -> returns 2 >gst_adapter_masked_scan_uint32 (adapter, 0xffff0000, 0x02030000, 0, 4); >// -> returns -1

Scan for pattern pattern with applied mask mask in the adapter data, starting from offset offset.

The bytes in pattern and mask are interpreted left-to-right, regardless of endianness. All four bytes of the pattern must be present in the adapter for it to match, even if the first or last bytes are masked out.

It is an error to call this function without making sure that there is enough data (offset+size bytes) in the adapter.

This function calls adapterMaskedScanUint32Peek passing Nothing for value.

maskedScanUint32Peek

adapterMaskedScanUint32Peek

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> Word32

mask: mask to apply to data before matching against pattern

-> Word32

pattern: pattern to match (after mask is applied)

-> Word64

offset: offset into the adapter data from which to start scanning, returns the last scanned position.

-> Word64

size: number of bytes to scan from offset

-> m (Int64, Word32)

Returns: offset of the first match, or -1 if no match was found.

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.

The bytes in pattern and mask are interpreted left-to-right, regardless of endianness. All four bytes of the pattern must be present in the adapter for it to match, even if the first or last bytes are masked out.

It is an error to call this function without making sure that there is enough data (offset+size bytes) in the adapter.

new

adapterNew

Arguments

:: (HasCallStack, MonadIO m)

=> m Adapter

Returns: a new Adapter

Creates a new Adapter. Free with objectUnref.

offsetAtDiscont

adapterOffsetAtDiscont

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> m Word64

Returns: The offset at the last discont or GST_BUFFER_OFFSET_NONE.

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

Since: 1.10

prevDts

adapterPrevDts

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> m (Word64, Word64)

Returns: The previously seen dts.

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.

prevDtsAtOffset

adapterPrevDtsAtOffset

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> Word64

offset: the offset in the adapter at which to get timestamp

-> m (Word64, Word64)

Returns: The previously seen dts at given offset.

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.

Since: 1.2

prevOffset

adapterPrevOffset

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> m (Word64, Word64)

Returns: The previous seen offset.

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.

Since: 1.10

prevPts

adapterPrevPts

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> m (Word64, Word64)

Returns: The previously seen pts.

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.

prevPtsAtOffset

adapterPrevPtsAtOffset

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> Word64

offset: the offset in the adapter at which to get timestamp

-> m (Word64, Word64)

Returns: The previously seen pts at given offset.

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.

Since: 1.2

ptsAtDiscont

adapterPtsAtDiscont

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> m Word64

Returns: The PTS at the last discont or GST_CLOCK_TIME_NONE.

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

Since: 1.10

push

adapterPush

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> Buffer

buf: a Buffer to add to queue in the adapter

-> m ()

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

take

adapterTake

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> m (Maybe ByteString)

Returns: oven-fresh hot data, or Nothing if nbytes bytes are not available

Returns a freshly allocated buffer containing the first nbytes bytes of the adapter. The returned bytes will be flushed from the adapter.

Caller owns returned value. g_free after usage.

Free-function: g_free

takeBuffer

adapterTakeBuffer

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> Word64

nbytes: the number of bytes to take

-> m (Maybe Buffer)

Returns: a Buffer containing the first nbytes of the adapter, or Nothing if nbytes bytes are not available. gst_buffer_unref() when no longer needed.

Returns a Buffer containing the first nbytes bytes of the adapter. The returned bytes will be flushed from the adapter. This function is potentially more performant than adapterTake 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.

Note that no assumptions should be made as to whether certain buffer flags such as the DISCONT flag are set on the returned buffer, or not. The caller needs to explicitly set or unset flags that should be set or unset.

Since 1.6 this will also copy over all GstMeta of the input buffers except for meta with the MetaFlagsPooled flag or with the "memory" tag.

Caller owns a reference to the returned buffer. gst_buffer_unref() after usage.

Free-function: gst_buffer_unref

takeBufferFast

adapterTakeBufferFast

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> Word64

nbytes: the number of bytes to take

-> m (Maybe Buffer)

Returns: a Buffer containing the first nbytes of the adapter, or Nothing if nbytes bytes are not available. gst_buffer_unref() when no longer needed.

Returns a Buffer containing the first nbytes of the adapter. The returned bytes will be flushed from the adapter. This function is potentially more performant than adapterTakeBuffer since it can reuse the memory in pushed buffers by subbuffering or merging. Unlike adapterTakeBuffer, the returned buffer may be composed of multiple non-contiguous Memory objects, no copies are made.

Note that no assumptions should be made as to whether certain buffer flags such as the DISCONT flag are set on the returned buffer, or not. The caller needs to explicitly set or unset flags that should be set or unset.

This will also copy over all GstMeta of the input buffers except for meta with the MetaFlagsPooled flag or with the "memory" tag.

This function can return buffer up to the return value of adapterAvailable without making copies if possible.

Caller owns a reference to the returned buffer. gst_buffer_unref() after usage.

Free-function: gst_buffer_unref

Since: 1.2

takeBufferList

adapterTakeBufferList

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> Word64

nbytes: the number of bytes to take

-> m (Maybe BufferList)

Returns: a BufferList of buffers containing the first nbytes of the adapter, or Nothing if nbytes bytes are not available

Returns a BufferList 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.

Caller owns the returned list. Call gst_buffer_list_unref() to free the list after usage.

Since: 1.6

takeList

adapterTakeList

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> Word64

nbytes: the number of bytes to take

-> m [Buffer]

Returns: a List of buffers containing the first nbytes of the adapter, or Nothing if nbytes bytes are not available

Returns a List 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.

Caller owns returned list and contained buffers. gst_buffer_unref() each buffer in the list before freeing the list after usage.

unmap

adapterUnmap

Arguments

:: (HasCallStack, MonadIO m, IsAdapter a)

=> a

adapter: a Adapter

-> m ()

Releases the memory obtained with the last adapterMap.