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Original commit message from CVS: 2005-07-15 Andy Wingo <wingo@pobox.com> * tools/gst-typefind.c: Update, add copyright block. * gst/base/gstbasesrc.c (gst_base_src_default_negotiate): Normalize and truncate caps before fixation. * gst/gstcaps.h: * gst/gstcaps.c (gst_caps_truncate): New function, destructively discards all but the first structure from its argument.
407 lines
7.7 KiB
Text
407 lines
7.7 KiB
Text
<!-- ##### 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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<example>
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<title>Creating a buffer for a video frame</title>
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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_MALLOCDATA (buffer) = g_alloc (size);
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GST_BUFFER_DATA (buffer) = GST_BUFFER_MALLOCDATA (buffer);
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...
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</programlisting>
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</example>
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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 data of a given size.
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</para>
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<para>
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If an element knows what pad you will push the buffer out on, it should use
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gst_pad_alloc_buffer() instead to create a buffer. This allows downstream
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elements to provide special buffers to write in, like hardware buffers.
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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_make_writable(). 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 12th, 2004 (0.8.5)
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</para>
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<!-- ##### SECTION See_Also ##### -->
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<para>
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#GstPad, #GstMiniObject
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</para>
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<!-- ##### SECTION Stability_Level ##### -->
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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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@mini_object:
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@data:
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@size:
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@timestamp:
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@duration:
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@caps:
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@offset:
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@offset_end:
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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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<!-- ##### ENUM GstBufferFlag ##### -->
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<para>
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</para>
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@GST_BUFFER_FLAG_READONLY:
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@GST_BUFFER_FLAG_ORIGINAL:
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@GST_BUFFER_FLAG_PREROLL:
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@GST_BUFFER_FLAG_DISCONT:
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@GST_BUFFER_FLAG_IN_CAPS:
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@GST_BUFFER_FLAG_GAP:
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@GST_BUFFER_FLAG_DELTA_UNIT:
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@GST_BUFFER_FLAG_LAST:
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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_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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<!-- ##### 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_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_DURATION ##### -->
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<para>
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Gets the duration in nanoseconds of the data in the buffer.
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Value will be GST_CLOCK_TIME_NONE if the duration is unknown.
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</para>
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@buf: a #GstBuffer to get the duration from.
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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 the beinning 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_OFFSET_END ##### -->
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<para>
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Gets the offset in the source file of the end 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_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_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_is_writable ##### -->
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<para>
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Tests if you can safely write data into a buffer's data array.
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</para>
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@buf: a #GstBuffer to check
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<!-- ##### MACRO gst_buffer_make_writable ##### -->
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<para>
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</para>
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@buf:
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<!-- ##### MACRO gst_buffer_replace ##### -->
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<para>
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</para>
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@obuf:
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@nbuf:
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<!-- ##### FUNCTION gst_buffer_get_caps ##### -->
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<para>
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</para>
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@buffer:
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@Returns:
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<!-- ##### FUNCTION gst_buffer_set_caps ##### -->
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<para>
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</para>
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@buffer:
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@caps:
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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_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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<!-- ##### MACRO GST_BUFFER_TRACE_NAME ##### -->
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<para>
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The name used for tracing memory allocations
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</para>
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<!-- ##### MACRO GST_BUFFER_OFFSET_NONE ##### -->
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<para>
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</para>
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<!-- ##### MACRO GST_BUFFER_DURATION_IS_VALID ##### -->
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<para>
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Tests if the duration is known.
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</para>
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@buffer: the #GstBuffer to check for the duration
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<!-- ##### MACRO GST_BUFFER_TIMESTAMP_IS_VALID ##### -->
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<para>
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Tests if the timestamp is known.
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</para>
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@buffer: the #GstBuffer to check for the timestamp
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<!-- ##### MACRO GST_BUFFER_OFFSET_IS_VALID ##### -->
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<para>
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</para>
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@buffer:
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<!-- ##### MACRO GST_BUFFER_OFFSET_END_IS_VALID ##### -->
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<para>
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</para>
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@buffer:
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<!-- ##### FUNCTION gst_buffer_stamp ##### -->
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<para>
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</para>
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@dest:
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@src:
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<!-- ##### FUNCTION gst_buffer_join ##### -->
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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_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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