GstBuffer
Data-passing buffer type, supporting sub-buffers.
Buffers are the basic unit of data transfer in GStreamer. The GstBuffer type
provides all the state necessary to define a region of memory as part of a
stream. Sub-buffers are also supported, allowing a smaller region of a
buffer to become its own buffer, with mechanisms in place to ensure that
neither memory space goes away.
Buffers are usually created with gst_buffer_new(). After a buffer has been
created one will typically allocate memory for it and set the size of the
buffer data. The following example creates a buffer that can hold a given
video frame with a given width, height and bits per plane.
Creating a buffer for a video frame
GstBuffer *buffer;
gint size, width, height, bpp;
...
size = width * height * bpp;
buffer = gst_buffer_new ();
GST_BUFFER_SIZE (buffer) = size;
GST_BUFFER_DATA (buffer) = g_alloc (size);
...
Alternatively, use gst_buffer_new_and_alloc()
to create a buffer with preallocated data of a given size.
If an element knows what pad you will push the buffer out on, it should use
gst_pad_alloc_buffer() instead to create a buffer. This allows downstream
elements to provide special buffers to write in, like hardware buffers.
gst_buffer_ref() is used to increase the refcount of a buffer. This must be
done when you want to keep a handle to the buffer after pushing it to the
next element.
To efficiently create a smaller buffer out of an existing one, you can
use gst_buffer_create_sub().
If the plug-in wants to modify the buffer in-place, it should first obtain
a buffer that is safe to modify by using gst_buffer_copy_on_write(). This
function is optimized so that a copy will only be made when it is necessary.
Several flags of the buffer can be set and unset with the GST_BUFFER_FLAG_SET()
and GST_BUFFER_FLAG_UNSET() macros. Use GST_BUFFER_FLAG_IS_SET() to test it
a certain #GstBufferFlag is set.
Buffers can be efficiently merged into a larger buffer with gst_buffer_merge() and
gst_buffer_span() if the gst_buffer_is_span_fast() function returns TRUE.
An element should either unref the buffer or push it out on a src pad
using gst_pad_push() (see #GstPad).
Buffers usually are freed by unreffing them with gst_buffer_unref().
Do not use gst_buffer_free() : this function effectively frees the buffer
regardless of the refcount, which is dangerous.
Last reviewed on August 12th, 2004 (0.8.5)
#GstBufferPool, #GstPad, #GstData
The basic structure of a buffer.
@mini_object:
@data:
@size:
@timestamp:
@duration:
@caps:
@offset:
@offset_end:
@Returns:
@size:
@Returns:
@GST_BUFFER_FLAG_READONLY:
@GST_BUFFER_FLAG_ORIGINAL:
@GST_BUFFER_FLAG_PREROLL:
@GST_BUFFER_FLAG_DISCONT:
@GST_BUFFER_FLAG_IN_CAPS:
@GST_BUFFER_FLAG_GAP:
@GST_BUFFER_FLAG_DELTA_UNIT:
@GST_BUFFER_FLAG_LAST:
Gets the flags from this buffer.
@buf: a #GstBuffer to retrieve the flags from.
Gives the status of a given flag of a buffer.
@buf: a #GstBuffer to query flags of.
@flag: the #GstBufferFlag to check.
Sets a buffer flag.
@buf: a #GstBuffer to modify flags of.
@flag: the #GstBufferFlag to set.
Clears a buffer flag.
@buf: a #GstBuffer to modify flags of.
@flag: the #GstBufferFlag to clear.
A convenience function to set the data and size on a buffer
@buf: The buffer to modify
@data: The data to set on the buffer
@size: The size to set on the buffer
Retrieves a pointer to the data element of this buffer.
@buf: a #GstBuffer to get data pointer of.
@Returns: the pointer to the actual data contents of the buffer.
Gets the size of the data in this buffer.
@buf: a #GstBuffer to get data size of.
Gets the timestamp for this buffer.
@buf: a #GstBuffer to get timestamp of.
Gets the duration in nanoseconds of the data in the buffer.
Value will be GST_CLOCK_TIME_NONE if the duration is unknown.
@buf: a #GstBuffer to get the duration from.
Gets the offset in the source file of the beinning of this buffer.
@buf: a #GstBuffer to get offset of.
Gets the offset in the source file of the end of this buffer.
@buf: a #GstBuffer to get offset of.
Increases the refcount of the given buffer by one.
@buf: a #GstBuffer to increase the refcount of.
Decreases the refcount of the buffer. If the refcount reaches 0, the buffer
will be freed.
@buf: a #GstBuffer to unref.
@dest:
@src:
Copies the given buffer using the copy function of the parent GstData structure.
@buf: a #GstBuffer to copy.
@Returns: a new #GstBuffer copy of the buffer.
Tests if you can safely write data into a buffer's data array.
@buf: a #GstBuffer to check
@parent:
@offset:
@size:
@Returns:
@buf1:
@buf2:
@Returns:
@buf1:
@offset:
@buf2:
@len:
@Returns:
@buf1:
@buf2:
@Returns:
@buffer:
@buffer:
@Returns:
The name used for tracing memory allocations
Tests if the duration is known.
@buffer: the #GstBuffer to check for the duration
Tests if the timestamp is known.
@buffer: the #GstBuffer to check for the timestamp
@buffer:
@buffer:
@buffer: