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421 lines
9 KiB
Plaintext
421 lines
9 KiB
Plaintext
<!-- ##### SECTION Title ##### -->
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GstBuffer
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<!-- ##### SECTION Short_Description ##### -->
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Data-passing buffer type, supporting sub-buffers.
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<!-- ##### SECTION Long_Description ##### -->
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<para>
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Buffers are the basic unit of data transfer in GStreamer. The GstBuffer type
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provides all the state necessary to define a region of memory as part of a
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stream. Sub-buffers are also supported, allowing a smaller region of a
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buffer to become its own buffer, with mechanisms in place to ensure that
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neither memory space goes away.
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</para>
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<para>
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Buffers are usually created with gst_buffer_new(). After a buffer has been
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created one will typically allocate memory for it and set the size of the
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buffer data. The following example creates a buffer that can hold a given
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video frame with a given width, height and bits per plane.
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<programlisting>
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GstBuffer *buffer;
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gint size, width, height, bpp;
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...
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size = width * height * bpp;
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buffer = gst_buffer_new ();
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GST_BUFFER_SIZE (buffer) = size;
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GST_BUFFER_DATA (buffer) = g_alloc (size);
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...
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</programlisting>
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</para>
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<para>
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Alternatively, use gst_buffer_new_and_alloc()
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to create a buffer with preallocated
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data of a given size.
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</para>
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<para>
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GstBuffers can also be created from a #GstBufferPool with
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gst_buffer_new_from_pool(). The bufferpool can be obtained from a
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peer element with gst_pad_get_bufferpool().
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</para>
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<para>
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gst_buffer_ref() is used to increase the refcount of a buffer. This must be
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done when you want to keep a handle to the buffer after pushing it to the
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next element.
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</para>
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<para>
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To efficiently create a smaller buffer out of an existing one, you can
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use gst_buffer_create_sub().
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</para>
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<para>
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If the plug-in wants to modify the buffer in-place, it should first obtain
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a buffer that is safe to modify by using gst_buffer_copy_on_write(). This
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function is optimized so that a copy will only be made when it is necessary.
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</para>
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<para>
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Several flags of the buffer can be set and unset with the GST_BUFFER_FLAG_SET()
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and GST_BUFFER_FLAG_UNSET() macros. Use GST_BUFFER_FLAG_IS_SET() to test it
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a certain #GstBufferFlag is set.
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</para>
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<para>
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Buffers can be efficiently merged into a larger buffer with gst_buffer_merge() and
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gst_buffer_span() if the gst_buffer_is_span_fast() function returns TRUE.
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</para>
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<para>
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An element should either unref the buffer or push it out on a src pad
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using gst_pad_push() (see #GstPad).
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Buffers usually are freed by unreffing them with gst_buffer_unref().
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Do not use gst_buffer_free() : this function effectively frees the buffer
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regardless of the refcount, which is dangerous.
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</para>
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<para>
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Last reviewed on August 30th, 2002 (0.4.0.1)
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</para>
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<!-- ##### SECTION See_Also ##### -->
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<para>
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#GstBufferPool, #GstPad, #GstData
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</para>
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<!-- ##### MACRO GST_BUFFER ##### -->
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<para>
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Casts an object to a GstBuffer.
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</para>
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@buf: an object to cast.
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@Returns: the #GstBuffer to which the given object points.
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<!-- ##### MACRO GST_IS_BUFFER ##### -->
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<para>
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Checks if the pointer is a GstBuffer.
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</para>
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@buf: a pointer to query.
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<!-- ##### MACRO GST_BUFFER_REFCOUNT ##### -->
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<para>
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Gets a handle to the refcount structure of the buffer.
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</para>
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@buf: a #GstBuffer to get the refcount structure of.
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<!-- ##### MACRO GST_BUFFER_REFCOUNT_VALUE ##### -->
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<para>
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Gets the current refcount value of the buffer.
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</para>
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@buf: a #GstBuffer to get the refcount value of.
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<!-- ##### MACRO GST_BUFFER_COPY_FUNC ##### -->
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<para>
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Calls the buffer-specific copy function on the given buffer.
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</para>
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@buf: a #GstBuffer to copy.
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<!-- ##### MACRO GST_BUFFER_FREE_FUNC ##### -->
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<para>
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Calls the buffer-specific free function on the given buffer.
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</para>
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@buf: a #GstBuffer to free.
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<!-- ##### MACRO GST_BUFFER_FLAGS ##### -->
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<para>
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Gets the flags from this buffer.
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</para>
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@buf: a #GstBuffer to retrieve the flags from.
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<!-- ##### MACRO GST_BUFFER_FLAG_IS_SET ##### -->
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<para>
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Gives the status of a given flag of a buffer.
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</para>
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@buf: a #GstBuffer to query flags of.
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@flag: the #GstBufferFlag to check.
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<!-- ##### MACRO GST_BUFFER_FLAG_SET ##### -->
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<para>
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Sets a buffer flag.
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</para>
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@buf: a #GstBuffer to modify flags of.
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@flag: the #GstBufferFlag to set.
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<!-- ##### MACRO GST_BUFFER_FLAG_UNSET ##### -->
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<para>
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Clears a buffer flag.
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</para>
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@buf: a #GstBuffer to modify flags of.
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@flag: the #GstBufferFlag to clear.
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<!-- ##### MACRO GST_BUFFER_DATA ##### -->
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<para>
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Retrieves a pointer to the data element of this buffer.
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</para>
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@buf: a #GstBuffer to get data pointer of.
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@Returns: the pointer to the actual data contents of the buffer.
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<!-- ##### MACRO GST_BUFFER_SIZE ##### -->
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<para>
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Gets the size of the data in this buffer.
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</para>
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@buf: a #GstBuffer to get data size of.
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<!-- ##### MACRO GST_BUFFER_MAXSIZE ##### -->
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<para>
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Gets the maximum size of this buffer.
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</para>
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@buf: a #GstBuffer to get maximum size of.
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<!-- ##### MACRO GST_BUFFER_TIMESTAMP ##### -->
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<para>
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Gets the timestamp for this buffer.
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</para>
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@buf: a #GstBuffer to get timestamp of.
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<!-- ##### MACRO GST_BUFFER_OFFSET ##### -->
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<para>
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Gets the offset in the source file of this buffer.
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</para>
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@buf: a #GstBuffer to get offset of.
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<!-- ##### MACRO GST_BUFFER_BUFFERPOOL ##### -->
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<para>
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Gets the bufferpool for this buffer.
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</para>
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@buf: a #GstBuffer to get the bufferpool of.
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@Returns: the #GstBufferPool of this buffer.
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<!-- ##### MACRO GST_BUFFER_POOL_PRIVATE ##### -->
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<para>
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Gets the bufferpool private data.
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</para>
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@buf: a #GstBuffer to get bufferpool's private data of.
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<!-- ##### ENUM GstBufferFlag ##### -->
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<para>
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A set of buffer flags used to describe properties of a #GstBuffer.
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</para>
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@GST_BUFFER_READONLY: the buffer is read-only.
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@GST_BUFFER_SUBBUFFER: the buffer is a subbuffer, the parent buffer can be
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found with the GST_BUFFER_POOL_PRIVATE() macro.
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@GST_BUFFER_ORIGINAL: buffer is not a copy of another buffer.
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@GST_BUFFER_DONTFREE: do not try to free the data when this buffer is
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unreferenced.
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@GST_BUFFER_DISCONTINUOUS: the buffer is the first one after a discontinuity
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in the stream.
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@GST_BUFFER_KEY_UNIT: the buffer holds a key unit, a unit that can be
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decoded independently of other buffers.
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@GST_BUFFER_PREROLL: the buffer should be decoded but not rendered, it is
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mainly used to resynchronise the stream.
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@GST_BUFFER_FLAG_LAST: additional flags can be added starting from this flag.
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<!-- ##### STRUCT GstBuffer ##### -->
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<para>
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The basic structure of a buffer.
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</para>
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@data_type:
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@data:
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@size:
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@maxsize:
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@timestamp:
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@offset:
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@pool:
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@pool_private:
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<!-- ##### FUNCTION gst_buffer_new ##### -->
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<para>
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</para>
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@Returns:
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<!-- ##### FUNCTION gst_buffer_new_and_alloc ##### -->
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<para>
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</para>
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@size:
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@Returns:
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<!-- ##### MACRO gst_buffer_set_data ##### -->
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<para>
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A convenience function to set the data and size on a buffer
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</para>
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@buf: The buffer to modify
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@data: The data to set on the buffer
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@size: The size to set on the buffer
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<!-- ##### FUNCTION gst_buffer_new_from_pool ##### -->
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<para>
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</para>
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@pool:
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@offset:
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@size:
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@Returns:
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<!-- ##### FUNCTION gst_buffer_default_free ##### -->
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<para>
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</para>
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@buffer:
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<!-- ##### FUNCTION gst_buffer_default_copy ##### -->
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<para>
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</para>
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@buffer:
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@Returns:
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<!-- ##### MACRO gst_buffer_ref ##### -->
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<para>
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Increases the refcount of the given buffer by one.
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</para>
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@buf: a #GstBuffer to increase the refcount of.
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<!-- ##### MACRO gst_buffer_ref_by_count ##### -->
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<para>
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Increases the refcount of the buffer by the given value.
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</para>
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@buf: a #GstBuffer to increase the refcount of.
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@c: the value to add to the refcount.
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<!-- ##### MACRO gst_buffer_unref ##### -->
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<para>
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Decreases the refcount of the buffer. If the refcount reaches 0, the buffer
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will be freed.
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</para>
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@buf: a #GstBuffer to unref.
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<!-- ##### MACRO gst_buffer_copy ##### -->
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<para>
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Copies the given buffer using the copy function of the parent GstData structure.
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</para>
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@buf: a #GstBuffer to copy.
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@Returns: a new #GstBuffer copy of the buffer.
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<!-- ##### MACRO gst_buffer_copy_on_write ##### -->
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<para>
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This function returns a buffer that is safe to write to.
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Copy the buffer if the refcount > 1 so that the newly
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created buffer can be safely written to.
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If the refcount is 1, this function just returns the original buffer.
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</para>
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@buf: a #GstBuffer to copy
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@Returns: the #GstBuffer that can safely be written to.
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<!-- ##### MACRO gst_buffer_free ##### -->
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<para>
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Frees the given buffer, regardless of the refcount.
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It is dangerous to use this function, you should use gst_buffer_unref() instead.
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</para>
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@buf: a #GstBuffer to free.
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<!-- ##### FUNCTION gst_buffer_create_sub ##### -->
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<para>
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</para>
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@parent:
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@offset:
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@size:
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@Returns:
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<!-- ##### FUNCTION gst_buffer_merge ##### -->
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<para>
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</para>
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@buf1:
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@buf2:
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@Returns:
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<!-- ##### FUNCTION gst_buffer_is_span_fast ##### -->
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<para>
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</para>
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@buf1:
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@buf2:
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@Returns:
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<!-- ##### FUNCTION gst_buffer_span ##### -->
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<para>
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</para>
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@buf1:
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@offset:
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@buf2:
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@len:
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@Returns:
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<!-- ##### FUNCTION gst_buffer_print_stats ##### -->
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<para>
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</para>
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