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
29 * type provides all the state necessary to define a region of memory as part
30 * of a 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
91 * offset, timestamp or caps, should use gst_buffer_make_metadata_writable(),
92 * which will create a subbuffer of the original buffer to ensure the caller
93 * has sole ownership, 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 = 0;
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 g_free (buffer->malloc_data);
188 gst_caps_replace (&GST_BUFFER_CAPS (buffer), NULL);
192 _gst_buffer_copy (GstBuffer * buffer)
197 g_return_val_if_fail (buffer != NULL, NULL);
199 /* create a fresh new buffer */
200 copy = gst_buffer_new ();
202 GST_CAT_LOG (GST_CAT_BUFFER, "copy %p to %p", buffer, copy);
204 /* copy relevant flags */
205 mask = GST_BUFFER_FLAG_PREROLL | GST_BUFFER_FLAG_IN_CAPS |
206 GST_BUFFER_FLAG_DELTA_UNIT | GST_BUFFER_FLAG_DISCONT |
208 GST_MINI_OBJECT_FLAGS (copy) |= GST_MINI_OBJECT_FLAGS (buffer) & mask;
210 /* we simply copy everything from our parent */
211 copy->data = g_memdup (buffer->data, buffer->size);
212 /* make sure it gets freed (even if the parent is subclassed, we return a
214 copy->malloc_data = copy->data;
216 copy->size = buffer->size;
218 GST_BUFFER_TIMESTAMP (copy) = GST_BUFFER_TIMESTAMP (buffer);
219 GST_BUFFER_DURATION (copy) = GST_BUFFER_DURATION (buffer);
220 GST_BUFFER_OFFSET (copy) = GST_BUFFER_OFFSET (buffer);
221 GST_BUFFER_OFFSET_END (copy) = GST_BUFFER_OFFSET_END (buffer);
223 if (GST_BUFFER_CAPS (buffer))
224 GST_BUFFER_CAPS (copy) = gst_caps_ref (GST_BUFFER_CAPS (buffer));
226 GST_BUFFER_CAPS (copy) = NULL;
232 gst_buffer_init (GTypeInstance * instance, gpointer g_class)
236 buffer = (GstBuffer *) instance;
238 GST_CAT_LOG (GST_CAT_BUFFER, "init %p", buffer);
240 GST_BUFFER_TIMESTAMP (buffer) = GST_CLOCK_TIME_NONE;
241 GST_BUFFER_DURATION (buffer) = GST_CLOCK_TIME_NONE;
242 GST_BUFFER_OFFSET (buffer) = GST_BUFFER_OFFSET_NONE;
243 GST_BUFFER_OFFSET_END (buffer) = GST_BUFFER_OFFSET_NONE;
249 * Creates a newly allocated buffer without any data.
252 * Returns: the new #GstBuffer.
255 gst_buffer_new (void)
259 newbuf = (GstBuffer *) gst_mini_object_new (GST_TYPE_BUFFER);
261 GST_CAT_LOG (GST_CAT_BUFFER, "new %p", newbuf);
267 * gst_buffer_new_and_alloc:
268 * @size: the size of the new buffer's data.
270 * Creates a newly allocated buffer with data of the given size.
271 * The buffer memory is not cleared.
273 * Note that when @size == 0, the buffer data pointer will be NULL.
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_CAST (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))
395 #define GST_SUBBUFFER_CAST(obj) ((GstSubBuffer *)(obj))
404 struct _GstSubBufferClass
406 GstBufferClass buffer_class;
409 static GstBufferClass *sub_parent_class;
411 static void gst_subbuffer_init (GTypeInstance * instance, gpointer g_class);
412 static void gst_subbuffer_class_init (gpointer g_class, gpointer class_data);
413 static void gst_subbuffer_finalize (GstSubBuffer * buffer);
416 gst_subbuffer_get_type (void)
418 static GType _gst_subbuffer_type = 0;
420 if (G_UNLIKELY (_gst_subbuffer_type == 0)) {
421 static const GTypeInfo subbuffer_info = {
422 sizeof (GstSubBufferClass),
425 gst_subbuffer_class_init,
428 sizeof (GstSubBuffer),
434 _gst_subbuffer_type = g_type_register_static (GST_TYPE_BUFFER,
435 "GstSubBuffer", &subbuffer_info, 0);
437 return _gst_subbuffer_type;
441 gst_subbuffer_class_init (gpointer g_class, gpointer class_data)
443 GstBufferClass *buffer_class = GST_BUFFER_CLASS (g_class);
445 sub_parent_class = g_type_class_peek_parent (g_class);
447 buffer_class->mini_object_class.finalize =
448 (GstMiniObjectFinalizeFunction) gst_subbuffer_finalize;
452 gst_subbuffer_finalize (GstSubBuffer * buffer)
454 gst_buffer_unref (buffer->parent);
456 GST_MINI_OBJECT_CLASS (sub_parent_class)->
457 finalize (GST_MINI_OBJECT_CAST (buffer));
461 gst_subbuffer_init (GTypeInstance * instance, gpointer g_class)
463 GST_BUFFER_FLAG_SET (GST_BUFFER_CAST (instance), GST_BUFFER_FLAG_READONLY);
467 * gst_buffer_create_sub:
468 * @parent: a #GstBuffer.
469 * @offset: the offset into parent #GstBuffer at which the new sub-buffer
471 * @size: the size of the new #GstBuffer sub-buffer, in bytes.
473 * Creates a sub-buffer from @parent at @offset and @size.
474 * This sub-buffer uses the actual memory space of the parent buffer.
475 * This function will copy the offset and timestamp fields when the
476 * offset is 0, else they are set to #GST_CLOCK_TIME_NONE/#GST_BUFFER_OFFSET_NONE.
477 * The duration field of the new buffer is set to #GST_CLOCK_TIME_NONE.
480 * Returns: the new #GstBuffer.
481 * Returns NULL if the arguments were invalid.
484 gst_buffer_create_sub (GstBuffer * buffer, guint offset, guint size)
486 GstSubBuffer *subbuffer;
489 g_return_val_if_fail (buffer != NULL, NULL);
490 g_return_val_if_fail (buffer->mini_object.refcount > 0, NULL);
491 g_return_val_if_fail (buffer->size >= offset + size, NULL);
493 /* find real parent */
494 if (GST_IS_SUBBUFFER (buffer)) {
495 parent = GST_SUBBUFFER_CAST (buffer)->parent;
499 gst_buffer_ref (parent);
501 /* create the new buffer */
502 subbuffer = (GstSubBuffer *) gst_mini_object_new (GST_TYPE_SUBBUFFER);
503 subbuffer->parent = parent;
505 GST_CAT_LOG (GST_CAT_BUFFER, "new subbuffer %p (parent %p)", subbuffer,
508 /* set the right values in the child */
509 GST_BUFFER_DATA (GST_BUFFER_CAST (subbuffer)) = buffer->data + offset;
510 GST_BUFFER_SIZE (GST_BUFFER_CAST (subbuffer)) = size;
512 /* we can copy the timestamp and offset if the new buffer starts at
515 GST_BUFFER_TIMESTAMP (subbuffer) = GST_BUFFER_TIMESTAMP (buffer);
516 GST_BUFFER_OFFSET (subbuffer) = GST_BUFFER_OFFSET (buffer);
518 GST_BUFFER_TIMESTAMP (subbuffer) = GST_CLOCK_TIME_NONE;
519 GST_BUFFER_OFFSET (subbuffer) = GST_BUFFER_OFFSET_NONE;
522 GST_BUFFER_DURATION (subbuffer) = GST_CLOCK_TIME_NONE;
523 GST_BUFFER_OFFSET_END (subbuffer) = GST_BUFFER_OFFSET_NONE;
525 GST_BUFFER_CAPS (subbuffer) = NULL;
527 return GST_BUFFER_CAST (subbuffer);
531 * gst_buffer_is_span_fast:
532 * @buf1: the first #GstBuffer.
533 * @buf2: the second #GstBuffer.
535 * Determines whether a gst_buffer_span() can be done without copying
536 * the contents, that is, whether the data areas are contiguous sub-buffers of
540 * Returns: TRUE if the buffers are contiguous,
541 * FALSE if a copy would be required.
544 gst_buffer_is_span_fast (GstBuffer * buf1, GstBuffer * buf2)
546 g_return_val_if_fail (buf1 != NULL && buf2 != NULL, FALSE);
547 g_return_val_if_fail (buf1->mini_object.refcount > 0, FALSE);
548 g_return_val_if_fail (buf2->mini_object.refcount > 0, FALSE);
550 /* it's only fast if we have subbuffers of the same parent */
551 return (GST_IS_SUBBUFFER (buf1) &&
552 GST_IS_SUBBUFFER (buf2) &&
553 (GST_SUBBUFFER_CAST (buf1)->parent == GST_SUBBUFFER_CAST (buf2)->parent)
554 && ((buf1->data + buf1->size) == buf2->data));
559 * @buf1: the first source #GstBuffer to merge.
560 * @offset: the offset in the first buffer from where the new
561 * buffer should start.
562 * @buf2: the second source #GstBuffer to merge.
563 * @len: the total length of the new buffer.
565 * Creates a new buffer that consists of part of buf1 and buf2.
566 * Logically, buf1 and buf2 are concatenated into a single larger
567 * buffer, and a new buffer is created at the given offset inside
568 * this space, with a given length.
570 * If the two source buffers are children of the same larger buffer,
571 * and are contiguous, the new buffer will be a child of the shared
572 * parent, and thus no copying is necessary. you can use
573 * gst_buffer_is_span_fast() to determine if a memcpy will be needed.
576 * Returns: the new #GstBuffer that spans the two source buffers.
577 * Returns NULL if the arguments are invalid.
580 gst_buffer_span (GstBuffer * buf1, guint32 offset, GstBuffer * buf2,
585 g_return_val_if_fail (buf1 != NULL && buf2 != NULL, NULL);
586 g_return_val_if_fail (buf1->mini_object.refcount > 0, NULL);
587 g_return_val_if_fail (buf2->mini_object.refcount > 0, NULL);
588 g_return_val_if_fail (len > 0, NULL);
589 g_return_val_if_fail (len <= buf1->size + buf2->size - offset, NULL);
591 /* if the two buffers have the same parent and are adjacent */
592 if (gst_buffer_is_span_fast (buf1, buf2)) {
593 GstBuffer *parent = GST_SUBBUFFER_CAST (buf1)->parent;
595 /* we simply create a subbuffer of the common parent */
596 newbuf = gst_buffer_create_sub (parent,
597 buf1->data - parent->data + offset, len);
599 GST_CAT_DEBUG (GST_CAT_BUFFER,
600 "slow path taken while spanning buffers %p and %p", buf1, buf2);
601 /* otherwise we simply have to brute-force copy the buffers */
602 newbuf = gst_buffer_new_and_alloc (len);
604 /* copy the first buffer's data across */
605 memcpy (newbuf->data, buf1->data + offset, buf1->size - offset);
606 /* copy the second buffer's data across */
607 memcpy (newbuf->data + (buf1->size - offset), buf2->data,
608 len - (buf1->size - offset));
610 /* if the offset is 0, the new buffer has the same timestamp as buf1 */
612 GST_BUFFER_OFFSET (newbuf) = GST_BUFFER_OFFSET (buf1);
613 GST_BUFFER_TIMESTAMP (newbuf) = GST_BUFFER_TIMESTAMP (buf1);
615 /* if we completely merged the two buffers (appended), we can
616 * calculate the duration too. Also make sure we's not messing with
617 * invalid DURATIONS */
618 if (buf1->size + buf2->size == len) {
619 if (GST_BUFFER_DURATION_IS_VALID (buf1) &&
620 GST_BUFFER_DURATION_IS_VALID (buf2)) {
622 GST_BUFFER_DURATION (newbuf) = GST_BUFFER_DURATION (buf1) +
623 GST_BUFFER_DURATION (buf2);
625 if (GST_BUFFER_OFFSET_END_IS_VALID (buf2)) {
627 GST_BUFFER_OFFSET_END (newbuf) = GST_BUFFER_OFFSET_END (buf2);