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 * The data pointed to by the buffer can be retrieved with the GST_BUFFER_DATA()
57 * macro. The size of the data can be found with GST_BUFFER_SIZE(). For buffers
58 * of size 0, the data pointer is undefined (usually NULL) and should never be used.
60 * If an element knows what pad you will push the buffer out on, it should use
61 * gst_pad_alloc_buffer() instead to create a buffer. This allows downstream
62 * elements to provide special buffers to write in, like hardware buffers.
64 * A buffer has a pointer to a #GstCaps describing the media type of the data
65 * in the buffer. Attach caps to the buffer with gst_buffer_set_caps(); this
66 * is typically done before pushing out a buffer using gst_pad_push() so that
67 * the downstream element knows the type of the buffer.
69 * A buffer will usually have a timestamp, and a duration, but neither of these
70 * are guaranteed (they may be set to #GST_CLOCK_TIME_NONE). Whenever a
71 * meaningful value can be given for these, they should be set. The timestamp
72 * and duration are measured in nanoseconds (they are #GstClockTime values).
74 * A buffer can also have one or both of a start and an end offset. These are
75 * media-type specific. For video buffers, the start offset will generally be
76 * the frame number. For audio buffers, it will be the number of samples
77 * produced so far. For compressed data, it could be the byte offset in a
78 * source or destination file. Likewise, the end offset will be the offset of
79 * the end of the buffer. These can only be meaningfully interpreted if you
80 * know the media type of the buffer (the #GstCaps set on it). Either or both
81 * can be set to #GST_BUFFER_OFFSET_NONE.
83 * gst_buffer_ref() is used to increase the refcount of a buffer. This must be
84 * done when you want to keep a handle to the buffer after pushing it to the
87 * To efficiently create a smaller buffer out of an existing one, you can
88 * use gst_buffer_create_sub().
90 * If a plug-in wants to modify the buffer data in-place, it should first obtain
91 * a buffer that is safe to modify by using gst_buffer_make_writable(). This
92 * function is optimized so that a copy will only be made when it is necessary.
94 * A plugin that only wishes to modify the metadata of a buffer, such as the
95 * offset, timestamp or caps, should use gst_buffer_make_metadata_writable(),
96 * which will create a subbuffer of the original buffer to ensure the caller
97 * has sole ownership, and not copy the buffer data.
99 * Several flags of the buffer can be set and unset with the
100 * GST_BUFFER_FLAG_SET() and GST_BUFFER_FLAG_UNSET() macros. Use
101 * GST_BUFFER_FLAG_IS_SET() to test if a certain #GstBufferFlag is set.
103 * Buffers can be efficiently merged into a larger buffer with
104 * gst_buffer_merge() and gst_buffer_span() if the gst_buffer_is_span_fast()
105 * function returns TRUE.
107 * An element should either unref the buffer or push it out on a src pad
108 * using gst_pad_push() (see #GstPad).
110 * Buffers are usually freed by unreffing them with gst_buffer_unref(). When
111 * the refcount drops to 0, any data pointed to by GST_BUFFER_MALLOCDATA() will
114 * Last reviewed on August 11th, 2006 (0.10.10)
116 #include "gst_private.h"
118 #include "gstbuffer.h"
120 #include "gstutils.h"
121 #include "gstminiobject.h"
123 static void gst_buffer_init (GTypeInstance * instance, gpointer g_class);
124 static void gst_buffer_class_init (gpointer g_class, gpointer class_data);
125 static void gst_buffer_finalize (GstBuffer * buffer);
126 static GstBuffer *_gst_buffer_copy (GstBuffer * buffer);
127 static GType gst_subbuffer_get_type (void);
129 static GType _gst_subbuffer_type = 0;
130 static GType _gst_buffer_type = 0;
133 _gst_buffer_initialize (void)
137 gst_buffer_get_type ();
138 gst_subbuffer_get_type ();
140 /* the GstMiniObject types need to be class_ref'd once before it can be
141 * done from multiple threads;
142 * see http://bugzilla.gnome.org/show_bug.cgi?id=304551 */
143 ptr = g_type_class_ref (GST_TYPE_BUFFER);
144 g_type_class_unref (ptr);
148 gst_buffer_get_type (void)
150 if (G_UNLIKELY (_gst_buffer_type == 0)) {
151 static const GTypeInfo buffer_info = {
152 sizeof (GstBufferClass),
155 gst_buffer_class_init,
164 _gst_buffer_type = g_type_register_static (GST_TYPE_MINI_OBJECT,
165 "GstBuffer", &buffer_info, 0);
167 return _gst_buffer_type;
171 gst_buffer_class_init (gpointer g_class, gpointer class_data)
173 GstBufferClass *buffer_class = GST_BUFFER_CLASS (g_class);
175 buffer_class->mini_object_class.copy =
176 (GstMiniObjectCopyFunction) _gst_buffer_copy;
177 buffer_class->mini_object_class.finalize =
178 (GstMiniObjectFinalizeFunction) gst_buffer_finalize;
183 gst_buffer_finalize (GstBuffer * buffer)
185 g_return_if_fail (buffer != NULL);
187 GST_CAT_LOG (GST_CAT_BUFFER, "finalize %p", buffer);
190 g_free (buffer->malloc_data);
192 gst_caps_replace (&GST_BUFFER_CAPS (buffer), NULL);
196 * gst_buffer_copy_metadata:
197 * @dest: a destination #GstBuffer
198 * @src: a source #GstBuffer
199 * @flags: flags indicating what metadata fields should be copied.
201 * Copies the metadata from @src into @dest. The data, size and mallocdata
202 * fields are not copied.
204 * @flags indicate which fields will be copied. Use #GST_BUFFER_COPY_ALL to copy
205 * all the metadata fields.
207 * This function is typically called from a custom buffer copy function after
208 * creating @dest and setting the data, size, mallocdata.
213 gst_buffer_copy_metadata (GstBuffer * dest, const GstBuffer * src,
214 GstBufferCopyFlags flags)
216 g_return_if_fail (dest != NULL);
217 g_return_if_fail (src != NULL);
219 GST_CAT_LOG (GST_CAT_BUFFER, "copy %p to %p", src, dest);
221 if (flags & GST_BUFFER_COPY_FLAGS) {
224 /* copy relevant flags */
225 mask = GST_BUFFER_FLAG_PREROLL | GST_BUFFER_FLAG_IN_CAPS |
226 GST_BUFFER_FLAG_DELTA_UNIT | GST_BUFFER_FLAG_DISCONT |
228 GST_MINI_OBJECT_FLAGS (dest) |= GST_MINI_OBJECT_FLAGS (src) & mask;
231 if (flags & GST_BUFFER_COPY_TIMESTAMPS) {
232 GST_BUFFER_TIMESTAMP (dest) = GST_BUFFER_TIMESTAMP (src);
233 GST_BUFFER_DURATION (dest) = GST_BUFFER_DURATION (src);
234 GST_BUFFER_OFFSET (dest) = GST_BUFFER_OFFSET (src);
235 GST_BUFFER_OFFSET_END (dest) = GST_BUFFER_OFFSET_END (src);
238 if (flags & GST_BUFFER_COPY_CAPS) {
239 if (GST_BUFFER_CAPS (src))
240 GST_BUFFER_CAPS (dest) = gst_caps_ref (GST_BUFFER_CAPS (src));
242 GST_BUFFER_CAPS (dest) = NULL;
247 _gst_buffer_copy (GstBuffer * buffer)
251 g_return_val_if_fail (buffer != NULL, NULL);
253 /* create a fresh new buffer */
254 copy = gst_buffer_new ();
256 /* we simply copy everything from our parent */
257 copy->data = g_memdup (buffer->data, buffer->size);
258 /* make sure it gets freed (even if the parent is subclassed, we return a
260 copy->malloc_data = copy->data;
261 copy->size = buffer->size;
263 gst_buffer_copy_metadata (copy, buffer, GST_BUFFER_COPY_ALL);
269 gst_buffer_init (GTypeInstance * instance, gpointer g_class)
273 buffer = (GstBuffer *) instance;
275 GST_CAT_LOG (GST_CAT_BUFFER, "init %p", buffer);
277 GST_BUFFER_TIMESTAMP (buffer) = GST_CLOCK_TIME_NONE;
278 GST_BUFFER_DURATION (buffer) = GST_CLOCK_TIME_NONE;
279 GST_BUFFER_OFFSET (buffer) = GST_BUFFER_OFFSET_NONE;
280 GST_BUFFER_OFFSET_END (buffer) = GST_BUFFER_OFFSET_NONE;
286 * Creates a newly allocated buffer without any data.
289 * Returns: the new #GstBuffer.
292 gst_buffer_new (void)
296 newbuf = (GstBuffer *) gst_mini_object_new (_gst_buffer_type);
298 GST_CAT_LOG (GST_CAT_BUFFER, "new %p", newbuf);
304 * gst_buffer_new_and_alloc:
305 * @size: the size of the new buffer's data.
307 * Creates a newly allocated buffer with data of the given size.
308 * The buffer memory is not cleared.
310 * Note that when @size == 0, the buffer data pointer will be NULL.
313 * Returns: the new #GstBuffer.
316 gst_buffer_new_and_alloc (guint size)
320 newbuf = gst_buffer_new ();
322 newbuf->malloc_data = g_malloc (size);
323 GST_BUFFER_DATA (newbuf) = newbuf->malloc_data;
324 GST_BUFFER_SIZE (newbuf) = size;
326 GST_CAT_LOG (GST_CAT_BUFFER, "new %p of size %d", newbuf, size);
332 * gst_buffer_get_caps:
333 * @buffer: a #GstBuffer.
335 * Gets the media type of the buffer. This can be NULL if there
336 * is no media type attached to this buffer.
338 * Returns: a reference to the #GstCaps. unref after usage.
339 * Returns NULL if there were no caps on this buffer.
341 /* FIXME can we make this threadsafe without a lock on the buffer?
342 * We can use compare and swap and atomic reads. */
344 gst_buffer_get_caps (GstBuffer * buffer)
348 g_return_val_if_fail (buffer != NULL, NULL);
350 ret = GST_BUFFER_CAPS (buffer);
359 * gst_buffer_set_caps:
360 * @buffer: a #GstBuffer.
363 * Sets the media type on the buffer. The refcount of the caps will
364 * be increased and any previous caps on the buffer will be
367 /* FIXME can we make this threadsafe without a lock on the buffer?
368 * We can use compare and swap and atomic reads. Another idea is to
369 * not attach the caps to the buffer but use an event to signal a caps
372 gst_buffer_set_caps (GstBuffer * buffer, GstCaps * caps)
374 g_return_if_fail (buffer != NULL);
376 gst_caps_replace (&GST_BUFFER_CAPS (buffer), caps);
380 * gst_buffer_is_metadata_writable:
383 * Similar to gst_buffer_is_writable, but this only ensures that the
384 * refcount of the buffer is 1, indicating that the caller is the sole
385 * owner and can change the buffer metadata, such as caps and timestamps.
387 * Returns: TRUE if the metadata is writable.
390 gst_buffer_is_metadata_writable (GstBuffer * buf)
392 return (GST_MINI_OBJECT_REFCOUNT_VALUE (GST_MINI_OBJECT_CAST (buf)) == 1);
396 * gst_buffer_make_metadata_writable:
399 * Similar to gst_buffer_make_writable, but does not ensure that the buffer
400 * data array is writable. Instead, this just ensures that the returned buffer
401 * is solely owned by the caller, by creating a subbuffer of the original
402 * buffer if necessary.
404 * After calling this function, @buf should not be referenced anymore. The
405 * result of this function has guaranteed writable metadata.
407 * Returns: A new #GstBuffer with writable metadata.
410 gst_buffer_make_metadata_writable (GstBuffer * buf)
414 if (gst_buffer_is_metadata_writable (buf)) {
417 ret = gst_buffer_create_sub (buf, 0, GST_BUFFER_SIZE (buf));
419 /* copy all the flags except IN_CAPS */
420 GST_BUFFER_FLAGS (ret) = GST_BUFFER_FLAGS (buf);
421 GST_BUFFER_FLAG_UNSET (ret, GST_BUFFER_FLAG_IN_CAPS);
422 /* data should always be set to READONLY */
423 GST_BUFFER_FLAG_SET (ret, GST_BUFFER_FLAG_READONLY);
425 gst_buffer_unref (buf);
431 typedef struct _GstSubBuffer GstSubBuffer;
432 typedef struct _GstSubBufferClass GstSubBufferClass;
434 #define GST_IS_SUBBUFFER(obj) (G_TYPE_CHECK_INSTANCE_TYPE ((obj), _gst_subbuffer_type))
435 #define GST_SUBBUFFER_CAST(obj) ((GstSubBuffer *)(obj))
444 struct _GstSubBufferClass
446 GstBufferClass buffer_class;
449 static GstBufferClass *sub_parent_class;
451 static void gst_subbuffer_init (GTypeInstance * instance, gpointer g_class);
452 static void gst_subbuffer_class_init (gpointer g_class, gpointer class_data);
453 static void gst_subbuffer_finalize (GstSubBuffer * buffer);
456 gst_subbuffer_get_type (void)
458 if (G_UNLIKELY (_gst_subbuffer_type == 0)) {
459 static const GTypeInfo subbuffer_info = {
460 sizeof (GstSubBufferClass),
463 gst_subbuffer_class_init,
466 sizeof (GstSubBuffer),
472 _gst_subbuffer_type = g_type_register_static (GST_TYPE_BUFFER,
473 "GstSubBuffer", &subbuffer_info, 0);
475 return _gst_subbuffer_type;
479 gst_subbuffer_class_init (gpointer g_class, gpointer class_data)
481 GstBufferClass *buffer_class = GST_BUFFER_CLASS (g_class);
483 sub_parent_class = g_type_class_peek_parent (g_class);
485 buffer_class->mini_object_class.finalize =
486 (GstMiniObjectFinalizeFunction) gst_subbuffer_finalize;
490 gst_subbuffer_finalize (GstSubBuffer * buffer)
492 gst_buffer_unref (buffer->parent);
494 GST_MINI_OBJECT_CLASS (sub_parent_class)->
495 finalize (GST_MINI_OBJECT_CAST (buffer));
499 gst_subbuffer_init (GTypeInstance * instance, gpointer g_class)
501 GST_BUFFER_FLAG_SET (GST_BUFFER_CAST (instance), GST_BUFFER_FLAG_READONLY);
505 * gst_buffer_create_sub:
506 * @parent: a #GstBuffer.
507 * @offset: the offset into parent #GstBuffer at which the new sub-buffer
509 * @size: the size of the new #GstBuffer sub-buffer, in bytes.
511 * Creates a sub-buffer from @parent at @offset and @size.
512 * This sub-buffer uses the actual memory space of the parent buffer.
513 * This function will copy the offset and timestamp fields when the
514 * offset is 0. If not, they will be set to #GST_CLOCK_TIME_NONE and
515 * #GST_BUFFER_OFFSET_NONE.
516 * If @offset equals 0 and @size equals the total size of @buffer, the
517 * duration and offset end fields are also copied. If not they will be set
518 * to #GST_CLOCK_TIME_NONE and #GST_BUFFER_OFFSET_NONE.
521 * Returns: the new #GstBuffer.
522 * Returns NULL if the arguments were invalid.
525 gst_buffer_create_sub (GstBuffer * buffer, guint offset, guint size)
527 GstSubBuffer *subbuffer;
531 g_return_val_if_fail (buffer != NULL, NULL);
532 g_return_val_if_fail (buffer->mini_object.refcount > 0, NULL);
533 g_return_val_if_fail (buffer->size >= offset + size, NULL);
535 /* find real parent */
536 if (GST_IS_SUBBUFFER (buffer)) {
537 parent = GST_SUBBUFFER_CAST (buffer)->parent;
541 gst_buffer_ref (parent);
543 /* create the new buffer */
544 subbuffer = (GstSubBuffer *) gst_mini_object_new (_gst_subbuffer_type);
545 subbuffer->parent = parent;
547 GST_CAT_LOG (GST_CAT_BUFFER, "new subbuffer %p (parent %p)", subbuffer,
550 /* set the right values in the child */
551 GST_BUFFER_DATA (GST_BUFFER_CAST (subbuffer)) = buffer->data + offset;
552 GST_BUFFER_SIZE (GST_BUFFER_CAST (subbuffer)) = size;
554 /* we can copy the timestamp and offset if the new buffer starts at
557 GST_BUFFER_TIMESTAMP (subbuffer) = GST_BUFFER_TIMESTAMP (buffer);
558 GST_BUFFER_OFFSET (subbuffer) = GST_BUFFER_OFFSET (buffer);
559 complete = (buffer->size == size);
561 GST_BUFFER_TIMESTAMP (subbuffer) = GST_CLOCK_TIME_NONE;
562 GST_BUFFER_OFFSET (subbuffer) = GST_BUFFER_OFFSET_NONE;
569 /* if we copied the complete buffer we can copy the duration,
570 * offset_end and caps as well */
571 GST_BUFFER_DURATION (subbuffer) = GST_BUFFER_DURATION (buffer);
572 GST_BUFFER_OFFSET_END (subbuffer) = GST_BUFFER_OFFSET_END (buffer);
573 if ((caps = GST_BUFFER_CAPS (buffer)))
575 GST_BUFFER_CAPS (subbuffer) = caps;
577 GST_BUFFER_DURATION (subbuffer) = GST_CLOCK_TIME_NONE;
578 GST_BUFFER_OFFSET_END (subbuffer) = GST_BUFFER_OFFSET_NONE;
579 GST_BUFFER_CAPS (subbuffer) = NULL;
581 return GST_BUFFER_CAST (subbuffer);
585 * gst_buffer_is_span_fast:
586 * @buf1: the first #GstBuffer.
587 * @buf2: the second #GstBuffer.
589 * Determines whether a gst_buffer_span() can be done without copying
590 * the contents, that is, whether the data areas are contiguous sub-buffers of
594 * Returns: TRUE if the buffers are contiguous,
595 * FALSE if a copy would be required.
598 gst_buffer_is_span_fast (GstBuffer * buf1, GstBuffer * buf2)
600 g_return_val_if_fail (buf1 != NULL && buf2 != NULL, FALSE);
601 g_return_val_if_fail (buf1->mini_object.refcount > 0, FALSE);
602 g_return_val_if_fail (buf2->mini_object.refcount > 0, FALSE);
604 /* it's only fast if we have subbuffers of the same parent */
605 return (GST_IS_SUBBUFFER (buf1) &&
606 GST_IS_SUBBUFFER (buf2) &&
607 (GST_SUBBUFFER_CAST (buf1)->parent == GST_SUBBUFFER_CAST (buf2)->parent)
608 && ((buf1->data + buf1->size) == buf2->data));
613 * @buf1: the first source #GstBuffer to merge.
614 * @offset: the offset in the first buffer from where the new
615 * buffer should start.
616 * @buf2: the second source #GstBuffer to merge.
617 * @len: the total length of the new buffer.
619 * Creates a new buffer that consists of part of buf1 and buf2.
620 * Logically, buf1 and buf2 are concatenated into a single larger
621 * buffer, and a new buffer is created at the given offset inside
622 * this space, with a given length.
624 * If the two source buffers are children of the same larger buffer,
625 * and are contiguous, the new buffer will be a child of the shared
626 * parent, and thus no copying is necessary. you can use
627 * gst_buffer_is_span_fast() to determine if a memcpy will be needed.
630 * Returns: the new #GstBuffer that spans the two source buffers.
631 * Returns NULL if the arguments are invalid.
634 gst_buffer_span (GstBuffer * buf1, guint32 offset, GstBuffer * buf2,
639 g_return_val_if_fail (buf1 != NULL && buf2 != NULL, NULL);
640 g_return_val_if_fail (buf1->mini_object.refcount > 0, NULL);
641 g_return_val_if_fail (buf2->mini_object.refcount > 0, NULL);
642 g_return_val_if_fail (len > 0, NULL);
643 g_return_val_if_fail (len <= buf1->size + buf2->size - offset, NULL);
645 /* if the two buffers have the same parent and are adjacent */
646 if (gst_buffer_is_span_fast (buf1, buf2)) {
647 GstBuffer *parent = GST_SUBBUFFER_CAST (buf1)->parent;
649 /* we simply create a subbuffer of the common parent */
650 newbuf = gst_buffer_create_sub (parent,
651 buf1->data - parent->data + offset, len);
653 GST_CAT_DEBUG (GST_CAT_BUFFER,
654 "slow path taken while spanning buffers %p and %p", buf1, buf2);
655 /* otherwise we simply have to brute-force copy the buffers */
656 newbuf = gst_buffer_new_and_alloc (len);
658 /* copy the first buffer's data across */
659 memcpy (newbuf->data, buf1->data + offset, buf1->size - offset);
660 /* copy the second buffer's data across */
661 memcpy (newbuf->data + (buf1->size - offset), buf2->data,
662 len - (buf1->size - offset));
664 /* if the offset is 0, the new buffer has the same timestamp as buf1 */
666 GST_BUFFER_OFFSET (newbuf) = GST_BUFFER_OFFSET (buf1);
667 GST_BUFFER_TIMESTAMP (newbuf) = GST_BUFFER_TIMESTAMP (buf1);
669 /* if we completely merged the two buffers (appended), we can
670 * calculate the duration too. Also make sure we's not messing with
671 * invalid DURATIONS */
672 if (buf1->size + buf2->size == len) {
673 if (GST_BUFFER_DURATION_IS_VALID (buf1) &&
674 GST_BUFFER_DURATION_IS_VALID (buf2)) {
676 GST_BUFFER_DURATION (newbuf) = GST_BUFFER_DURATION (buf1) +
677 GST_BUFFER_DURATION (buf2);
679 if (GST_BUFFER_OFFSET_END_IS_VALID (buf2)) {
681 GST_BUFFER_OFFSET_END (newbuf) = GST_BUFFER_OFFSET_END (buf2);