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);
124 static GType gst_subbuffer_get_type (void);
127 _gst_buffer_initialize (void)
131 gst_buffer_get_type ();
132 gst_subbuffer_get_type ();
134 /* the GstMiniObject types need to be class_ref'd once before it can be
135 * done from multiple threads;
136 * see http://bugzilla.gnome.org/show_bug.cgi?id=304551 */
137 ptr = g_type_class_ref (GST_TYPE_BUFFER);
138 g_type_class_unref (ptr);
142 gst_buffer_get_type (void)
144 static GType _gst_buffer_type;
146 if (G_UNLIKELY (_gst_buffer_type == 0)) {
147 static const GTypeInfo buffer_info = {
148 sizeof (GstBufferClass),
151 gst_buffer_class_init,
160 _gst_buffer_type = g_type_register_static (GST_TYPE_MINI_OBJECT,
161 "GstBuffer", &buffer_info, 0);
163 return _gst_buffer_type;
167 gst_buffer_class_init (gpointer g_class, gpointer class_data)
169 GstBufferClass *buffer_class = GST_BUFFER_CLASS (g_class);
171 buffer_class->mini_object_class.copy =
172 (GstMiniObjectCopyFunction) _gst_buffer_copy;
173 buffer_class->mini_object_class.finalize =
174 (GstMiniObjectFinalizeFunction) gst_buffer_finalize;
179 gst_buffer_finalize (GstBuffer * buffer)
181 g_return_if_fail (buffer != NULL);
183 GST_CAT_LOG (GST_CAT_BUFFER, "finalize %p", buffer);
186 if (buffer->malloc_data) {
187 g_free (buffer->malloc_data);
190 gst_caps_replace (&GST_BUFFER_CAPS (buffer), NULL);
194 _gst_buffer_copy (GstBuffer * buffer)
199 g_return_val_if_fail (buffer != NULL, NULL);
201 /* create a fresh new buffer */
202 copy = gst_buffer_new ();
204 GST_CAT_LOG (GST_CAT_BUFFER, "copy %p to %p", buffer, copy);
206 /* copy relevant flags */
207 mask = GST_BUFFER_FLAG_PREROLL | GST_BUFFER_FLAG_IN_CAPS |
208 GST_BUFFER_FLAG_DELTA_UNIT | GST_BUFFER_FLAG_DISCONT |
210 GST_MINI_OBJECT (copy)->flags |= GST_MINI_OBJECT (buffer)->flags & mask;
212 /* we simply copy everything from our parent */
213 copy->data = g_memdup (buffer->data, buffer->size);
214 /* make sure it gets freed (even if the parent is subclassed, we return a
216 copy->malloc_data = copy->data;
218 copy->size = buffer->size;
220 GST_BUFFER_TIMESTAMP (copy) = GST_BUFFER_TIMESTAMP (buffer);
221 GST_BUFFER_DURATION (copy) = GST_BUFFER_DURATION (buffer);
222 GST_BUFFER_OFFSET (copy) = GST_BUFFER_OFFSET (buffer);
223 GST_BUFFER_OFFSET_END (copy) = GST_BUFFER_OFFSET_END (buffer);
225 if (GST_BUFFER_CAPS (buffer))
226 GST_BUFFER_CAPS (copy) = gst_caps_ref (GST_BUFFER_CAPS (buffer));
228 GST_BUFFER_CAPS (copy) = NULL;
234 gst_buffer_init (GTypeInstance * instance, gpointer g_class)
238 buffer = (GstBuffer *) instance;
240 GST_CAT_LOG (GST_CAT_BUFFER, "init %p", buffer);
242 GST_BUFFER_TIMESTAMP (buffer) = GST_CLOCK_TIME_NONE;
243 GST_BUFFER_DURATION (buffer) = GST_CLOCK_TIME_NONE;
244 GST_BUFFER_OFFSET (buffer) = GST_BUFFER_OFFSET_NONE;
245 GST_BUFFER_OFFSET_END (buffer) = GST_BUFFER_OFFSET_NONE;
251 * Creates a newly allocated buffer without any data.
254 * Returns: the new #GstBuffer.
257 gst_buffer_new (void)
261 newbuf = (GstBuffer *) gst_mini_object_new (GST_TYPE_BUFFER);
263 GST_CAT_LOG (GST_CAT_BUFFER, "new %p", newbuf);
269 * gst_buffer_new_and_alloc:
270 * @size: the size of the new buffer's data.
272 * Creates a newly allocated buffer with data of the given size.
273 * The buffer memory is not cleared.
276 * Returns: the new #GstBuffer.
279 gst_buffer_new_and_alloc (guint size)
283 newbuf = gst_buffer_new ();
285 newbuf->malloc_data = g_malloc (size);
286 GST_BUFFER_DATA (newbuf) = newbuf->malloc_data;
287 GST_BUFFER_SIZE (newbuf) = size;
289 GST_CAT_LOG (GST_CAT_BUFFER, "new %p of size %d", newbuf, size);
295 * gst_buffer_get_caps:
296 * @buffer: a #GstBuffer.
298 * Gets the media type of the buffer. This can be NULL if there
299 * is no media type attached to this buffer.
301 * Returns: a reference to the #GstCaps. unref after usage.
302 * Returns NULL if there were no caps on this buffer.
304 /* FIXME can we make this threadsafe without a lock on the buffer?
305 * We can use compare and swap and atomic reads. */
307 gst_buffer_get_caps (GstBuffer * buffer)
311 g_return_val_if_fail (buffer != NULL, NULL);
313 ret = GST_BUFFER_CAPS (buffer);
322 * gst_buffer_set_caps:
323 * @buffer: a #GstBuffer.
326 * Sets the media type on the buffer. The refcount of the caps will
327 * be increased and any previous caps on the buffer will be
330 /* FIXME can we make this threadsafe without a lock on the buffer?
331 * We can use compare and swap and atomic reads. Another idea is to
332 * not attach the caps to the buffer but use an event to signal a caps
335 gst_buffer_set_caps (GstBuffer * buffer, GstCaps * caps)
337 g_return_if_fail (buffer != NULL);
339 gst_caps_replace (&GST_BUFFER_CAPS (buffer), caps);
343 * gst_buffer_is_metadata_writable:
346 * Similar to gst_buffer_is_writable, but this only ensures that the
347 * refcount of the buffer is 1, indicating that the caller is the sole
348 * owner and can change the buffer metadata, such as caps and timestamps.
350 * Returns: TRUE if the metadata is writable.
353 gst_buffer_is_metadata_writable (GstBuffer * buf)
355 return (GST_MINI_OBJECT_REFCOUNT_VALUE (GST_MINI_OBJECT (buf)) == 1);
359 * gst_buffer_make_metadata_writable:
362 * Similar to gst_buffer_make_writable, but does not ensure that the buffer
363 * data array is writable. Instead, this just ensures that the returned buffer
364 * is solely owned by the caller, by creating a subbuffer of the original
365 * buffer if necessary.
367 * After calling this function, @buf should not be referenced anymore.
369 * Returns: A new #GstBuffer with writable metadata.
372 gst_buffer_make_metadata_writable (GstBuffer * buf)
376 if (gst_buffer_is_metadata_writable (buf)) {
379 ret = gst_buffer_create_sub (buf, 0, GST_BUFFER_SIZE (buf));
380 GST_BUFFER_FLAGS (ret) = GST_BUFFER_FLAGS (buf);
381 GST_BUFFER_FLAG_UNSET (ret, GST_BUFFER_FLAG_IN_CAPS);
382 gst_buffer_unref (buf);
388 typedef struct _GstSubBuffer GstSubBuffer;
389 typedef struct _GstSubBufferClass GstSubBufferClass;
391 #define GST_TYPE_SUBBUFFER (gst_subbuffer_get_type())
393 #define GST_IS_SUBBUFFER(obj) (G_TYPE_CHECK_INSTANCE_TYPE ((obj), GST_TYPE_SUBBUFFER))
394 #define GST_SUBBUFFER(obj) (G_TYPE_CHECK_INSTANCE_CAST ((obj), GST_TYPE_SUBBUFFER, GstSubBuffer))
403 struct _GstSubBufferClass
405 GstBufferClass buffer_class;
408 static GstBufferClass *sub_parent_class;
410 static void gst_subbuffer_init (GTypeInstance * instance, gpointer g_class);
411 static void gst_subbuffer_class_init (gpointer g_class, gpointer class_data);
412 static void gst_subbuffer_finalize (GstSubBuffer * buffer);
415 gst_subbuffer_get_type (void)
417 static GType _gst_subbuffer_type = 0;
419 if (G_UNLIKELY (_gst_subbuffer_type == 0)) {
420 static const GTypeInfo subbuffer_info = {
421 sizeof (GstSubBufferClass),
424 gst_subbuffer_class_init,
427 sizeof (GstSubBuffer),
433 _gst_subbuffer_type = g_type_register_static (GST_TYPE_BUFFER,
434 "GstSubBuffer", &subbuffer_info, 0);
436 return _gst_subbuffer_type;
440 gst_subbuffer_class_init (gpointer g_class, gpointer class_data)
442 GstBufferClass *buffer_class = GST_BUFFER_CLASS (g_class);
444 sub_parent_class = g_type_class_peek_parent (g_class);
446 buffer_class->mini_object_class.finalize =
447 (GstMiniObjectFinalizeFunction) gst_subbuffer_finalize;
451 gst_subbuffer_finalize (GstSubBuffer * buffer)
453 gst_buffer_unref (buffer->parent);
455 GST_MINI_OBJECT_CLASS (sub_parent_class)->finalize (GST_MINI_OBJECT (buffer));
459 gst_subbuffer_init (GTypeInstance * instance, gpointer g_class)
461 GST_BUFFER_FLAG_SET (GST_BUFFER_CAST (instance), GST_BUFFER_FLAG_READONLY);
465 * gst_buffer_create_sub:
466 * @parent: a #GstBuffer.
467 * @offset: the offset into parent #GstBuffer at which the new sub-buffer
469 * @size: the size of the new #GstBuffer sub-buffer, in bytes (with size > 0).
471 * Creates a sub-buffer from @parent at @offset and @size.
472 * This sub-buffer uses the actual memory space of the parent buffer.
473 * This function will copy the offset and timestamp fields when the
474 * offset is 0, else they are set to #GST_CLOCK_TIME_NONE/#GST_BUFFER_OFFSET_NONE.
475 * The duration field of the new buffer is set to #GST_CLOCK_TIME_NONE.
478 * Returns: the new #GstBuffer.
479 * Returns NULL if the arguments were invalid.
482 gst_buffer_create_sub (GstBuffer * buffer, guint offset, guint size)
484 GstSubBuffer *subbuffer;
487 g_return_val_if_fail (buffer != NULL, NULL);
488 g_return_val_if_fail (buffer->mini_object.refcount > 0, NULL);
489 g_return_val_if_fail (size > 0, NULL);
490 g_return_val_if_fail (buffer->size >= offset + size, NULL);
492 /* find real parent */
493 if (GST_IS_SUBBUFFER (buffer)) {
494 parent = GST_SUBBUFFER (buffer)->parent;
498 gst_buffer_ref (parent);
500 /* create the new buffer */
501 subbuffer = (GstSubBuffer *) gst_mini_object_new (GST_TYPE_SUBBUFFER);
502 subbuffer->parent = parent;
504 GST_CAT_LOG (GST_CAT_BUFFER, "new subbuffer %p (parent %p)", subbuffer,
507 /* set the right values in the child */
508 GST_BUFFER_DATA (GST_BUFFER_CAST (subbuffer)) = buffer->data + offset;
509 GST_BUFFER_SIZE (GST_BUFFER_CAST (subbuffer)) = size;
511 /* we can copy the timestamp and offset if the new buffer starts at
514 GST_BUFFER_TIMESTAMP (subbuffer) = GST_BUFFER_TIMESTAMP (buffer);
515 GST_BUFFER_OFFSET (subbuffer) = GST_BUFFER_OFFSET (buffer);
517 GST_BUFFER_TIMESTAMP (subbuffer) = GST_CLOCK_TIME_NONE;
518 GST_BUFFER_OFFSET (subbuffer) = GST_BUFFER_OFFSET_NONE;
521 GST_BUFFER_DURATION (subbuffer) = GST_CLOCK_TIME_NONE;
522 GST_BUFFER_OFFSET_END (subbuffer) = GST_BUFFER_OFFSET_NONE;
524 GST_BUFFER_CAPS (subbuffer) = NULL;
526 return GST_BUFFER_CAST (subbuffer);
530 * gst_buffer_is_span_fast:
531 * @buf1: the first #GstBuffer.
532 * @buf2: the second #GstBuffer.
534 * Determines whether a gst_buffer_span() can be done without copying
535 * the contents, that is, whether the data areas are contiguous sub-buffers of
539 * Returns: TRUE if the buffers are contiguous,
540 * FALSE if a copy would be required.
543 gst_buffer_is_span_fast (GstBuffer * buf1, GstBuffer * buf2)
545 g_return_val_if_fail (buf1 != NULL && buf2 != NULL, FALSE);
546 g_return_val_if_fail (buf1->mini_object.refcount > 0, FALSE);
547 g_return_val_if_fail (buf2->mini_object.refcount > 0, FALSE);
549 /* it's only fast if we have subbuffers of the same parent */
550 return (GST_IS_SUBBUFFER (buf1) &&
551 GST_IS_SUBBUFFER (buf2) &&
552 (GST_SUBBUFFER (buf1)->parent == GST_SUBBUFFER (buf2)->parent) &&
553 ((buf1->data + buf1->size) == buf2->data));
558 * @buf1: the first source #GstBuffer to merge.
559 * @offset: the offset in the first buffer from where the new
560 * buffer should start.
561 * @buf2: the second source #GstBuffer to merge.
562 * @len: the total length of the new buffer.
564 * Creates a new buffer that consists of part of buf1 and buf2.
565 * Logically, buf1 and buf2 are concatenated into a single larger
566 * buffer, and a new buffer is created at the given offset inside
567 * this space, with a given length.
569 * If the two source buffers are children of the same larger buffer,
570 * and are contiguous, the new buffer will be a child of the shared
571 * parent, and thus no copying is necessary. you can use
572 * gst_buffer_is_span_fast() to determine if a memcpy will be needed.
575 * Returns: the new #GstBuffer that spans the two source buffers.
576 * Returns NULL if the arguments are invalid.
579 gst_buffer_span (GstBuffer * buf1, guint32 offset, GstBuffer * buf2,
584 g_return_val_if_fail (buf1 != NULL && buf2 != NULL, NULL);
585 g_return_val_if_fail (buf1->mini_object.refcount > 0, NULL);
586 g_return_val_if_fail (buf2->mini_object.refcount > 0, NULL);
587 g_return_val_if_fail (len > 0, NULL);
588 g_return_val_if_fail (len <= buf1->size + buf2->size - offset, NULL);
590 /* if the two buffers have the same parent and are adjacent */
591 if (gst_buffer_is_span_fast (buf1, buf2)) {
592 GstBuffer *parent = GST_SUBBUFFER (buf1)->parent;
594 /* we simply create a subbuffer of the common parent */
595 newbuf = gst_buffer_create_sub (parent,
596 buf1->data - parent->data + offset, len);
598 GST_CAT_DEBUG (GST_CAT_BUFFER,
599 "slow path taken while spanning buffers %p and %p", buf1, buf2);
600 /* otherwise we simply have to brute-force copy the buffers */
601 newbuf = gst_buffer_new_and_alloc (len);
603 /* copy the first buffer's data across */
604 memcpy (newbuf->data, buf1->data + offset, buf1->size - offset);
605 /* copy the second buffer's data across */
606 memcpy (newbuf->data + (buf1->size - offset), buf2->data,
607 len - (buf1->size - offset));
609 /* if the offset is 0, the new buffer has the same timestamp as buf1 */
611 GST_BUFFER_OFFSET (newbuf) = GST_BUFFER_OFFSET (buf1);
612 GST_BUFFER_TIMESTAMP (newbuf) = GST_BUFFER_TIMESTAMP (buf1);
614 /* if we completely merged the two buffers (appended), we can
615 * calculate the duration too. Also make sure we's not messing with
616 * invalid DURATIONS */
617 if (buf1->size + buf2->size == len) {
618 if (GST_BUFFER_DURATION_IS_VALID (buf1) &&
619 GST_BUFFER_DURATION_IS_VALID (buf2)) {
621 GST_BUFFER_DURATION (newbuf) = GST_BUFFER_DURATION (buf1) +
622 GST_BUFFER_DURATION (buf2);
624 if (GST_BUFFER_OFFSET_END_IS_VALID (buf2)) {
626 GST_BUFFER_OFFSET_END (newbuf) = GST_BUFFER_OFFSET_END (buf2);