2 * Copyright (C) 1999,2000 Erik Walthinsen <omega@cse.ogi.edu>
3 * 2000 Wim Taymans <wtay@chello.be>
5 * gstbuffer.c: Buffer operations
7 * This library is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Library General Public
9 * License as published by the Free Software Foundation; either
10 * version 2 of the License, or (at your option) any later version.
12 * This library is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Library General Public License for more details.
17 * You should have received a copy of the GNU Library General Public
18 * License along with this library; if not, write to the
19 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
20 * Boston, MA 02111-1307, USA.
25 * @short_description: Data-passing buffer type, supporting sub-buffers.
26 * @see_also: #GstPad, #GstMiniObject
28 * Buffers are the basic unit of data transfer in GStreamer. The #GstBuffer type
29 * provides all the state necessary to define a region of memory as part of a
30 * stream. Sub-buffers are also supported, allowing a smaller region of a
31 * buffer to become its own buffer, with mechanisms in place to ensure that
32 * neither memory space goes away prematurely.
34 * Buffers are usually created with gst_buffer_new(). After a buffer has been
35 * created one will typically allocate memory for it and set the size of the
36 * buffer data. The following example creates a buffer that can hold a given
37 * video frame with a given width, height and bits per plane.
39 * <title>Creating a buffer for a video frame</title>
42 * gint size, width, height, bpp;
44 * size = width * height * bpp;
45 * buffer = gst_buffer_new ();
46 * GST_BUFFER_SIZE (buffer) = size;
47 * GST_BUFFER_MALLOCDATA (buffer) = g_malloc (size);
48 * GST_BUFFER_DATA (buffer) = GST_BUFFER_MALLOCDATA (buffer);
53 * Alternatively, use gst_buffer_new_and_alloc()
54 * to create a buffer with preallocated data of a given size.
56 * If an element knows what pad you will push the buffer out on, it should use
57 * gst_pad_alloc_buffer() instead to create a buffer. This allows downstream
58 * elements to provide special buffers to write in, like hardware buffers.
60 * A buffer has a pointer to a #GstCaps describing the media type of the data
61 * in the buffer. Attach caps to the buffer with gst_buffer_set_caps(); this
62 * is typically done before pushing out a buffer using gst_pad_push() so that
63 * the downstream element knows the type of the buffer.
65 * A buffer will usually have a timestamp, and a duration, but neither of these
66 * are guaranteed (they may be set to #GST_CLOCK_TIME_NONE). Whenever a
67 * meaningful value can be given for these, they should be set. The timestamp
68 * and duration are measured in nanoseconds (they are #GstClockTime values).
70 * A buffer can also have one or both of a start and an end offset. These are
71 * media-type specific. For video buffers, the start offset will generally be
72 * the frame number. For audio buffers, it will be the number of samples
73 * produced so far. For compressed data, it could be the byte offset in a
74 * source or destination file. Likewise, the end offset will be the offset of
75 * the end of the buffer. These can only be meaningfully interpreted if you
76 * know the media type of the buffer (the #GstCaps set on it). Either or both
77 * can be set to #GST_BUFFER_OFFSET_NONE.
79 * gst_buffer_ref() is used to increase the refcount of a buffer. This must be
80 * done when you want to keep a handle to the buffer after pushing it to the
83 * To efficiently create a smaller buffer out of an existing one, you can
84 * use gst_buffer_create_sub().
86 * If a plug-in wants to modify the buffer data in-place, it should first obtain
87 * a buffer that is safe to modify by using gst_buffer_make_writable(). This
88 * function is optimized so that a copy will only be made when it is necessary.
90 * A plugin that only wishes to modify the metadata of a buffer, such as the offset,
91 * timestamp or caps, should use gst_buffer_make_metadata_writable(), which will
92 * create a subbuffer of the original buffer to ensure the caller has sole ownership,
93 * and not copy the buffer data.
95 * Several flags of the buffer can be set and unset with the
96 * GST_BUFFER_FLAG_SET() and GST_BUFFER_FLAG_UNSET() macros. Use
97 * GST_BUFFER_FLAG_IS_SET() to test if a certain #GstBufferFlag is set.
99 * Buffers can be efficiently merged into a larger buffer with
100 * gst_buffer_merge() and gst_buffer_span() if the gst_buffer_is_span_fast()
101 * function returns TRUE.
103 * An element should either unref the buffer or push it out on a src pad
104 * using gst_pad_push() (see #GstPad).
106 * Buffers are usually freed by unreffing them with gst_buffer_unref(). When
107 * the refcount drops to 0, any data pointed to by GST_BUFFER_MALLOCDATA() will
110 * Last reviewed on November 23th, 2005 (0.9.5)
112 #include "gst_private.h"
114 #include "gstbuffer.h"
116 #include "gstutils.h"
117 #include "gstminiobject.h"
120 static void gst_buffer_init (GTypeInstance * instance, gpointer g_class);
121 static void gst_buffer_class_init (gpointer g_class, gpointer class_data);
122 static void gst_buffer_finalize (GstBuffer * buffer);
123 static GstBuffer *_gst_buffer_copy (GstBuffer * buffer);
127 _gst_buffer_initialize (void)
131 gst_buffer_get_type ();
133 /* the GstMiniObject types need to be class_ref'd once before it can be
134 * done from multiple threads;
135 * see http://bugzilla.gnome.org/show_bug.cgi?id=304551 */
136 ptr = g_type_class_ref (GST_TYPE_BUFFER);
137 g_type_class_unref (ptr);
141 gst_buffer_get_type (void)
143 static GType _gst_buffer_type;
145 if (G_UNLIKELY (_gst_buffer_type == 0)) {
146 static const GTypeInfo buffer_info = {
147 sizeof (GstBufferClass),
150 gst_buffer_class_init,
159 _gst_buffer_type = g_type_register_static (GST_TYPE_MINI_OBJECT,
160 "GstBuffer", &buffer_info, 0);
162 return _gst_buffer_type;
166 gst_buffer_class_init (gpointer g_class, gpointer class_data)
168 GstBufferClass *buffer_class = GST_BUFFER_CLASS (g_class);
170 buffer_class->mini_object_class.copy =
171 (GstMiniObjectCopyFunction) _gst_buffer_copy;
172 buffer_class->mini_object_class.finalize =
173 (GstMiniObjectFinalizeFunction) gst_buffer_finalize;
178 gst_buffer_finalize (GstBuffer * buffer)
180 g_return_if_fail (buffer != NULL);
182 GST_CAT_LOG (GST_CAT_BUFFER, "finalize %p", buffer);
185 if (buffer->malloc_data) {
186 g_free (buffer->malloc_data);
189 gst_caps_replace (&GST_BUFFER_CAPS (buffer), NULL);
193 _gst_buffer_copy (GstBuffer * buffer)
198 g_return_val_if_fail (buffer != NULL, NULL);
200 /* create a fresh new buffer */
201 copy = gst_buffer_new ();
203 GST_CAT_LOG (GST_CAT_BUFFER, "copy %p to %p", buffer, copy);
205 /* copy relevant flags */
206 mask = GST_BUFFER_FLAG_PREROLL | GST_BUFFER_FLAG_IN_CAPS |
207 GST_BUFFER_FLAG_DELTA_UNIT | GST_BUFFER_FLAG_DISCONT |
209 GST_MINI_OBJECT (copy)->flags |= GST_MINI_OBJECT (buffer)->flags & mask;
211 /* we simply copy everything from our parent */
212 copy->data = g_memdup (buffer->data, buffer->size);
213 /* make sure it gets freed (even if the parent is subclassed, we return a
215 copy->malloc_data = copy->data;
217 copy->size = buffer->size;
219 GST_BUFFER_TIMESTAMP (copy) = GST_BUFFER_TIMESTAMP (buffer);
220 GST_BUFFER_DURATION (copy) = GST_BUFFER_DURATION (buffer);
221 GST_BUFFER_OFFSET (copy) = GST_BUFFER_OFFSET (buffer);
222 GST_BUFFER_OFFSET_END (copy) = GST_BUFFER_OFFSET_END (buffer);
224 if (GST_BUFFER_CAPS (buffer))
225 GST_BUFFER_CAPS (copy) = gst_caps_ref (GST_BUFFER_CAPS (buffer));
227 GST_BUFFER_CAPS (copy) = NULL;
233 gst_buffer_init (GTypeInstance * instance, gpointer g_class)
237 buffer = (GstBuffer *) instance;
239 GST_CAT_LOG (GST_CAT_BUFFER, "init %p", buffer);
241 GST_BUFFER_TIMESTAMP (buffer) = GST_CLOCK_TIME_NONE;
242 GST_BUFFER_DURATION (buffer) = GST_CLOCK_TIME_NONE;
243 GST_BUFFER_OFFSET (buffer) = GST_BUFFER_OFFSET_NONE;
244 GST_BUFFER_OFFSET_END (buffer) = GST_BUFFER_OFFSET_NONE;
250 * Creates a newly allocated buffer without any data.
253 * Returns: the new #GstBuffer.
256 gst_buffer_new (void)
260 newbuf = (GstBuffer *) gst_mini_object_new (GST_TYPE_BUFFER);
262 GST_CAT_LOG (GST_CAT_BUFFER, "new %p", newbuf);
268 * gst_buffer_new_and_alloc:
269 * @size: the size of the new buffer's data.
271 * Creates a newly allocated buffer with data of the given size.
272 * The buffer memory is not cleared.
275 * Returns: the new #GstBuffer.
278 gst_buffer_new_and_alloc (guint size)
282 newbuf = gst_buffer_new ();
284 newbuf->malloc_data = g_malloc (size);
285 GST_BUFFER_DATA (newbuf) = newbuf->malloc_data;
286 GST_BUFFER_SIZE (newbuf) = size;
288 GST_CAT_LOG (GST_CAT_BUFFER, "new %p of size %d", newbuf, size);
294 * gst_buffer_get_caps:
295 * @buffer: a #GstBuffer.
297 * Gets the media type of the buffer. This can be NULL if there
298 * is no media type attached to this buffer.
300 * Returns: a reference to the #GstCaps. unref after usage.
301 * Returns NULL if there were no caps on this buffer.
303 /* FIXME can we make this threadsafe without a lock on the buffer?
304 * We can use compare and swap and atomic reads. */
306 gst_buffer_get_caps (GstBuffer * buffer)
310 g_return_val_if_fail (buffer != NULL, NULL);
312 ret = GST_BUFFER_CAPS (buffer);
321 * gst_buffer_set_caps:
322 * @buffer: a #GstBuffer.
325 * Sets the media type on the buffer. The refcount of the caps will
326 * be increased and any previous caps on the buffer will be
329 /* FIXME can we make this threadsafe without a lock on the buffer?
330 * We can use compare and swap and atomic reads. Another idea is to
331 * not attach the caps to the buffer but use an event to signal a caps
334 gst_buffer_set_caps (GstBuffer * buffer, GstCaps * caps)
336 g_return_if_fail (buffer != NULL);
338 gst_caps_replace (&GST_BUFFER_CAPS (buffer), caps);
342 * gst_buffer_is_metadata_writable:
345 * Similar to gst_buffer_is_writable, but this only ensures that the
346 * refcount of the buffer is 1, indicating that the caller is the sole
347 * owner and can change the buffer metadata, such as caps and timestamps.
349 * Returns: TRUE if the metadata is writable.
352 gst_buffer_is_metadata_writable (GstBuffer * buf)
354 return (GST_MINI_OBJECT_REFCOUNT_VALUE (GST_MINI_OBJECT (buf)) == 1);
358 * gst_buffer_make_metadata_writable:
361 * Similar to gst_buffer_make_writable, but does not ensure that the buffer
362 * data array is writable. Instead, this just ensures that the returned buffer
363 * is solely owned by the caller, by creating a subbuffer of the original
364 * buffer if necessary.
366 * After calling this function, @buf should not be referenced anymore.
368 * Returns: A new #GstBuffer with writable metadata.
371 gst_buffer_make_metadata_writable (GstBuffer * buf)
375 if (gst_buffer_is_metadata_writable (buf)) {
378 ret = gst_buffer_create_sub (buf, 0, GST_BUFFER_SIZE (buf));
379 gst_buffer_unref (buf);
385 typedef struct _GstSubBuffer GstSubBuffer;
386 typedef struct _GstSubBufferClass GstSubBufferClass;
388 #define GST_TYPE_SUBBUFFER (gst_subbuffer_get_type())
390 #define GST_IS_SUBBUFFER(obj) (G_TYPE_CHECK_INSTANCE_TYPE ((obj), GST_TYPE_SUBBUFFER))
391 #define GST_SUBBUFFER(obj) (G_TYPE_CHECK_INSTANCE_CAST ((obj), GST_TYPE_SUBBUFFER, GstSubBuffer))
400 struct _GstSubBufferClass
402 GstBufferClass buffer_class;
405 static GstBufferClass *sub_parent_class;
407 static void gst_subbuffer_init (GTypeInstance * instance, gpointer g_class);
408 static void gst_subbuffer_class_init (gpointer g_class, gpointer class_data);
409 static void gst_subbuffer_finalize (GstSubBuffer * buffer);
412 gst_subbuffer_get_type (void)
414 static GType _gst_subbuffer_type = 0;
416 if (G_UNLIKELY (_gst_subbuffer_type == 0)) {
417 static const GTypeInfo subbuffer_info = {
418 sizeof (GstSubBufferClass),
421 gst_subbuffer_class_init,
424 sizeof (GstSubBuffer),
430 _gst_subbuffer_type = g_type_register_static (GST_TYPE_BUFFER,
431 "GstSubBuffer", &subbuffer_info, 0);
433 return _gst_subbuffer_type;
437 gst_subbuffer_class_init (gpointer g_class, gpointer class_data)
439 GstBufferClass *buffer_class = GST_BUFFER_CLASS (g_class);
441 sub_parent_class = g_type_class_peek_parent (g_class);
443 buffer_class->mini_object_class.finalize =
444 (GstMiniObjectFinalizeFunction) gst_subbuffer_finalize;
448 gst_subbuffer_finalize (GstSubBuffer * buffer)
450 gst_buffer_unref (buffer->parent);
452 GST_MINI_OBJECT_CLASS (sub_parent_class)->finalize (GST_MINI_OBJECT (buffer));
456 gst_subbuffer_init (GTypeInstance * instance, gpointer g_class)
458 GST_BUFFER_FLAG_SET (GST_BUFFER_CAST (instance), GST_BUFFER_FLAG_READONLY);
462 * gst_buffer_create_sub:
463 * @parent: a #GstBuffer.
464 * @offset: the offset into parent #GstBuffer at which the new sub-buffer
466 * @size: the size of the new #GstBuffer sub-buffer, in bytes (with size > 0).
468 * Creates a sub-buffer from @parent at @offset and @size.
469 * This sub-buffer uses the actual memory space of the parent buffer.
470 * This function will copy the offset and timestamp fields when the
471 * offset is 0, else they are set to #GST_CLOCK_TIME_NONE/#GST_BUFFER_OFFSET_NONE.
472 * The duration field of the new buffer is set to #GST_CLOCK_TIME_NONE.
475 * Returns: the new #GstBuffer.
476 * Returns NULL if the arguments were invalid.
479 gst_buffer_create_sub (GstBuffer * buffer, guint offset, guint size)
481 GstSubBuffer *subbuffer;
484 g_return_val_if_fail (buffer != NULL, NULL);
485 g_return_val_if_fail (buffer->mini_object.refcount > 0, NULL);
486 g_return_val_if_fail (size > 0, NULL);
487 g_return_val_if_fail (buffer->size >= offset + size, NULL);
489 /* find real parent */
490 if (GST_IS_SUBBUFFER (buffer)) {
491 parent = GST_SUBBUFFER (buffer)->parent;
495 gst_buffer_ref (parent);
497 /* create the new buffer */
498 subbuffer = (GstSubBuffer *) gst_mini_object_new (GST_TYPE_SUBBUFFER);
499 subbuffer->parent = parent;
501 GST_CAT_LOG (GST_CAT_BUFFER, "new subbuffer %p (parent %p)", subbuffer,
504 /* set the right values in the child */
505 GST_BUFFER_DATA (GST_BUFFER_CAST (subbuffer)) = buffer->data + offset;
506 GST_BUFFER_SIZE (GST_BUFFER_CAST (subbuffer)) = size;
508 /* we can copy the timestamp and offset if the new buffer starts at
511 GST_BUFFER_TIMESTAMP (subbuffer) = GST_BUFFER_TIMESTAMP (buffer);
512 GST_BUFFER_OFFSET (subbuffer) = GST_BUFFER_OFFSET (buffer);
514 GST_BUFFER_TIMESTAMP (subbuffer) = GST_CLOCK_TIME_NONE;
515 GST_BUFFER_OFFSET (subbuffer) = GST_BUFFER_OFFSET_NONE;
518 GST_BUFFER_DURATION (subbuffer) = GST_CLOCK_TIME_NONE;
519 GST_BUFFER_OFFSET_END (subbuffer) = GST_BUFFER_OFFSET_NONE;
521 GST_BUFFER_CAPS (subbuffer) = NULL;
523 return GST_BUFFER_CAST (subbuffer);
527 * gst_buffer_is_span_fast:
528 * @buf1: the first #GstBuffer.
529 * @buf2: the second #GstBuffer.
531 * Determines whether a gst_buffer_span() can be done without copying
532 * the contents, that is, whether the data areas are contiguous sub-buffers of
536 * Returns: TRUE if the buffers are contiguous,
537 * FALSE if a copy would be required.
540 gst_buffer_is_span_fast (GstBuffer * buf1, GstBuffer * buf2)
542 g_return_val_if_fail (buf1 != NULL && buf2 != NULL, FALSE);
543 g_return_val_if_fail (buf1->mini_object.refcount > 0, FALSE);
544 g_return_val_if_fail (buf2->mini_object.refcount > 0, FALSE);
546 /* it's only fast if we have subbuffers of the same parent */
547 return (GST_IS_SUBBUFFER (buf1) &&
548 GST_IS_SUBBUFFER (buf2) &&
549 (GST_SUBBUFFER (buf1)->parent == GST_SUBBUFFER (buf2)->parent) &&
550 ((buf1->data + buf1->size) == buf2->data));
555 * @buf1: the first source #GstBuffer to merge.
556 * @offset: the offset in the first buffer from where the new
557 * buffer should start.
558 * @buf2: the second source #GstBuffer to merge.
559 * @len: the total length of the new buffer.
561 * Creates a new buffer that consists of part of buf1 and buf2.
562 * Logically, buf1 and buf2 are concatenated into a single larger
563 * buffer, and a new buffer is created at the given offset inside
564 * this space, with a given length.
566 * If the two source buffers are children of the same larger buffer,
567 * and are contiguous, the new buffer will be a child of the shared
568 * parent, and thus no copying is necessary. you can use
569 * gst_buffer_is_span_fast() to determine if a memcpy will be needed.
572 * Returns: the new #GstBuffer that spans the two source buffers.
573 * Returns NULL if the arguments are invalid.
576 gst_buffer_span (GstBuffer * buf1, guint32 offset, GstBuffer * buf2,
581 g_return_val_if_fail (buf1 != NULL && buf2 != NULL, NULL);
582 g_return_val_if_fail (buf1->mini_object.refcount > 0, NULL);
583 g_return_val_if_fail (buf2->mini_object.refcount > 0, NULL);
584 g_return_val_if_fail (len > 0, NULL);
585 g_return_val_if_fail (len <= buf1->size + buf2->size - offset, NULL);
587 /* if the two buffers have the same parent and are adjacent */
588 if (gst_buffer_is_span_fast (buf1, buf2)) {
589 GstBuffer *parent = GST_SUBBUFFER (buf1)->parent;
591 /* we simply create a subbuffer of the common parent */
592 newbuf = gst_buffer_create_sub (parent,
593 buf1->data - parent->data + offset, len);
595 GST_CAT_DEBUG (GST_CAT_BUFFER,
596 "slow path taken while spanning buffers %p and %p", buf1, buf2);
597 /* otherwise we simply have to brute-force copy the buffers */
598 newbuf = gst_buffer_new_and_alloc (len);
600 /* copy the first buffer's data across */
601 memcpy (newbuf->data, buf1->data + offset, buf1->size - offset);
602 /* copy the second buffer's data across */
603 memcpy (newbuf->data + (buf1->size - offset), buf2->data,
604 len - (buf1->size - offset));
606 /* if the offset is 0, the new buffer has the same timestamp as buf1 */
608 GST_BUFFER_OFFSET (newbuf) = GST_BUFFER_OFFSET (buf1);
609 GST_BUFFER_TIMESTAMP (newbuf) = GST_BUFFER_TIMESTAMP (buf1);
611 /* if we completely merged the two buffers (appended), we can
612 * calculate the duration too. Also make sure we's not messing with
613 * invalid DURATIONS */
614 if (buf1->size + buf2->size == len) {
615 if (GST_BUFFER_DURATION_IS_VALID (buf1) &&
616 GST_BUFFER_DURATION_IS_VALID (buf2)) {
618 GST_BUFFER_DURATION (newbuf) = GST_BUFFER_DURATION (buf1) +
619 GST_BUFFER_DURATION (buf2);
621 if (GST_BUFFER_OFFSET_END_IS_VALID (buf2)) {
623 GST_BUFFER_OFFSET_END (newbuf) = GST_BUFFER_OFFSET_END (buf2);