:right-sidebar: True Adapter =================================================================== .. currentmodule:: gi.repository.GstBase .. class:: Adapter(**properties: ~typing.Any) :no-contents-entry: Superclasses: :class:`~gi.repository.GObject.Object` 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 :func:`~gi.repository.GstBase.Adapter.new`. It can be freed again with :func:`~gi.repository.GObject.GObject.Object.unref`. The theory of operation is like this: All buffers received are put into the adapter using :func:`~gi.repository.GstBase.Adapter.push` and the data is then read back in chunks of the desired size using :func:`~gi.repository.GstBase.Adapter.map`/:func:`~gi.repository.GstBase.Adapter.unmap` and/or :func:`~gi.repository.GstBase.Adapter.copy`. After the data has been processed, it is freed using :func:`~gi.repository.GstBase.Adapter.unmap`. Other methods such as :func:`~gi.repository.GstBase.Adapter.take` and :func:`~gi.repository.GstBase.Adapter.take_buffer` combine :func:`~gi.repository.GstBase.Adapter.map` and :func:`~gi.repository.GstBase.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: .. code-block:: C :dedent: 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 :obj:`~gi.repository.GstBase.Adapter` is the libvisual element. An element using :obj:`~gi.repository.GstBase.Adapter` in its sink pad chain function should ensure that when the FLUSH_STOP event is received, that any queued data is cleared using :func:`~gi.repository.GstBase.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 :func:`~gi.repository.GstBase.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 :func:`~gi.repository.GstBase.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 :func:`~gi.repository.GstBase.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 :func:`~gi.repository.GstBase.Adapter.pts_at_discont`, :func:`~gi.repository.GstBase.Adapter.dts_at_discont` and :func:`~gi.repository.GstBase.Adapter.offset_at_discont`. The number of bytes that were consumed since then can be queried with :func:`~gi.repository.GstBase.Adapter.distance_from_discont`. A last thing to note is that while :obj:`~gi.repository.GstBase.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 :func:`~gi.repository.GstBase.Adapter.available_fast` are provided to help speed up such cases should you want to. To avoid repeated memory allocations, :func:`~gi.repository.GstBase.Adapter.copy` can be used to copy data into a (statically allocated) user provided buffer. :obj:`~gi.repository.GstBase.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 :obj:`~gi.repository.GstBase.Adapter` is inside one pad's chain function, in which case access is serialized via the pad's STREAM_LOCK. Note that :func:`~gi.repository.GstBase.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. Constructors ------------ .. rst-class:: interim-class .. class:: Adapter :no-index: .. classmethod:: new() -> ~gi.repository.GstBase.Adapter Creates a new :obj:`~gi.repository.GstBase.Adapter`\. Free with :func:`~gi.repository.GObject.GObject.Object.unref`. Methods ------- .. rst-class:: interim-class .. class:: Adapter :no-index: .. method:: available() -> int Gets the maximum amount of bytes available, that is it returns the maximum value that can be supplied to :func:`~gi.repository.GstBase.Adapter.map` without that function returning :const:`None`. .. method:: available_fast() -> int Gets the maximum number of bytes that are immediately available without requiring any expensive operations (like copying the data into a temporary buffer). .. method:: clear() -> None Removes all buffers from ``adapter``\. .. method:: distance_from_discont() -> int Get the distance in bytes since the last buffer with the %GST_BUFFER_FLAG_DISCONT flag. The distance will be reset to 0 for all buffers with %GST_BUFFER_FLAG_DISCONT on them, and then calculated for all other following buffers based on their size. .. versionadded:: 1.10 .. method:: dts_at_discont() -> int Get the DTS that was on the last buffer with the GST_BUFFER_FLAG_DISCONT flag, or GST_CLOCK_TIME_NONE. .. versionadded:: 1.10 .. method:: flush(flush: int) -> None Flushes the first ``flush`` bytes in the ``adapter``\. The caller must ensure that at least this many bytes are available. See also: :func:`~gi.repository.GstBase.Adapter.map`, :func:`~gi.repository.GstBase.Adapter.unmap` :param flush: the number of bytes to flush .. method:: get_buffer(nbytes: int) -> ~gi.repository.Gst.Buffer | None Returns a :obj:`~gi.repository.Gst.Buffer` containing the first ``nbytes`` of the ``adapter``\, but does not flush them from the adapter. See :func:`~gi.repository.GstBase.Adapter.take_buffer` for details. Caller owns a reference to the returned buffer. gst_buffer_unref() after usage. Free-function: gst_buffer_unref .. versionadded:: 1.6 :param nbytes: the number of bytes to get .. method:: get_buffer_fast(nbytes: int) -> ~gi.repository.Gst.Buffer | None Returns a :obj:`~gi.repository.Gst.Buffer` containing the first ``nbytes`` of the ``adapter``\, but does not flush them from the adapter. See :func:`~gi.repository.GstBase.Adapter.take_buffer_fast` for details. Caller owns a reference to the returned buffer. gst_buffer_unref() after usage. Free-function: gst_buffer_unref .. versionadded:: 1.6 :param nbytes: the number of bytes to get .. method:: get_buffer_list(nbytes: int) -> ~gi.repository.Gst.BufferList | None Returns a :obj:`~gi.repository.Gst.BufferList` of buffers containing the first ``nbytes`` bytes of the ``adapter`` but does not flush them from the adapter. See :func:`~gi.repository.GstBase.Adapter.take_buffer_list` for details. Caller owns the returned list. Call gst_buffer_list_unref() to free the list after usage. .. versionadded:: 1.6 :param nbytes: the number of bytes to get .. method:: get_list(nbytes: int) -> list[~gi.repository.Gst.Buffer] | None Returns a ``GList`` of buffers containing the first ``nbytes`` bytes of the ``adapter``\, but does not flush them from the adapter. See :func:`~gi.repository.GstBase.Adapter.take_list` for details. Caller owns returned list and contained buffers. gst_buffer_unref() each buffer in the list before freeing the list after usage. .. versionadded:: 1.6 :param nbytes: the number of bytes to get .. method:: map() -> list[int] | None 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 :obj:`~gi.repository.Gst.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 :func:`~gi.repository.GstBase.Adapter.take`, which returns a freshly-allocated buffer that you can set as :obj:`~gi.repository.Gst.Buffer` memory or the potentially more performant :func:`~gi.repository.GstBase.Adapter.take_buffer`. Returns :const:`None` if ``size`` bytes are not available. .. method:: masked_scan_uint32(mask: int, pattern: int, offset: int, size: int) -> int 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 :func:`~gi.repository.GstBase.Adapter.masked_scan_uint32_peek` passing :const:`None` for value. :param mask: mask to apply to data before matching against ``pattern`` :param pattern: pattern to match (after mask is applied) :param offset: offset into the adapter data from which to start scanning, returns the last scanned position. :param size: number of bytes to scan from offset .. method:: masked_scan_uint32_peek(mask: int, pattern: int, offset: int, size: int) -> ~typing.Tuple[int, int] 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. :param mask: mask to apply to data before matching against ``pattern`` :param pattern: pattern to match (after mask is applied) :param offset: offset into the adapter data from which to start scanning, returns the last scanned position. :param size: number of bytes to scan from offset .. method:: offset_at_discont() -> int Get the offset that was on the last buffer with the GST_BUFFER_FLAG_DISCONT flag, or GST_BUFFER_OFFSET_NONE. .. versionadded:: 1.10 .. method:: prev_dts() -> ~typing.Tuple[int, int] 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. .. method:: prev_dts_at_offset(offset: int) -> ~typing.Tuple[int, int] 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. .. versionadded:: 1.2 :param offset: the offset in the adapter at which to get timestamp .. method:: prev_offset() -> ~typing.Tuple[int, int] 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. .. versionadded:: 1.10 .. method:: prev_pts() -> ~typing.Tuple[int, int] 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. .. method:: prev_pts_at_offset(offset: int) -> ~typing.Tuple[int, int] 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. .. versionadded:: 1.2 :param offset: the offset in the adapter at which to get timestamp .. method:: pts_at_discont() -> int Get the PTS that was on the last buffer with the GST_BUFFER_FLAG_DISCONT flag, or GST_CLOCK_TIME_NONE. .. versionadded:: 1.10 .. method:: push(buf: ~gi.repository.Gst.Buffer) -> None Adds the data from ``buf`` to the data stored inside ``adapter`` and takes ownership of the buffer. :param buf: a :obj:`~gi.repository.Gst.Buffer` to add to queue in the adapter .. method:: take() -> list[int] | None 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 .. method:: take_buffer(nbytes: int) -> ~gi.repository.Gst.Buffer | None Returns a :obj:`~gi.repository.Gst.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 :func:`~gi.repository.GstBase.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. 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 %GST_META_FLAG_POOLED flag or with the "memory" tag. Caller owns a reference to the returned buffer. gst_buffer_unref() after usage. Free-function: gst_buffer_unref :param nbytes: the number of bytes to take .. method:: take_buffer_fast(nbytes: int) -> ~gi.repository.Gst.Buffer | None Returns a :obj:`~gi.repository.Gst.Buffer` containing the first ``nbytes`` of the ``adapter``\. The returned bytes will be flushed from the adapter. This function is potentially more performant than :func:`~gi.repository.GstBase.Adapter.take_buffer` since it can reuse the memory in pushed buffers by subbuffering or merging. Unlike :func:`~gi.repository.GstBase.Adapter.take_buffer`, the returned buffer may be composed of multiple non-contiguous :obj:`~gi.repository.Gst.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 %GST_META_FLAG_POOLED flag or with the "memory" tag. This function can return buffer up to the return value of :func:`~gi.repository.GstBase.Adapter.available` without making copies if possible. Caller owns a reference to the returned buffer. gst_buffer_unref() after usage. Free-function: gst_buffer_unref .. versionadded:: 1.2 :param nbytes: the number of bytes to take .. method:: take_buffer_list(nbytes: int) -> ~gi.repository.Gst.BufferList | None Returns a :obj:`~gi.repository.Gst.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. .. versionadded:: 1.6 :param nbytes: the number of bytes to take .. method:: take_list(nbytes: int) -> list[~gi.repository.Gst.Buffer] | None 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. Caller owns returned list and contained buffers. gst_buffer_unref() each buffer in the list before freeing the list after usage. :param nbytes: the number of bytes to take .. method:: unmap() -> None Releases the memory obtained with the last :func:`~gi.repository.GstBase.Adapter.map`.