gstreamer/gst/gstbuffer.c
2011-11-08 13:13:55 +01:00

1615 lines
44 KiB
C

/* GStreamer
* Copyright (C) 1999,2000 Erik Walthinsen <omega@cse.ogi.edu>
* 2000 Wim Taymans <wtay@chello.be>
*
* gstbuffer.c: Buffer operations
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public
* License along with this library; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*/
/**
* SECTION:gstbuffer
* @short_description: Data-passing buffer type, supporting sub-buffers.
* @see_also: #GstPad, #GstMiniObject, #GstBufferPool
*
* Buffers are the basic unit of data transfer in GStreamer. The #GstBuffer
* type provides all the state necessary to define the regions of memory as
* part of a stream. Region copies 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 prematurely.
*
* Buffers are usually created with gst_buffer_new(). After a buffer has been
* created one will typically allocate memory for it and add it to the buffer.
* The following example creates a buffer that can hold a given video frame
* with a given width, height and bits per plane.
* <example>
* <title>Creating a buffer for a video frame</title>
* <programlisting>
* GstBuffer *buffer;
* GstMemory *memory;
* gint size, width, height, bpp;
* ...
* size = width * height * bpp;
* buffer = gst_buffer_new ();
* memory = gst_allocator_alloc (NULL, size, 0);
* gst_buffer_take_memory (buffer, -1, memory);
* ...
* </programlisting>
* </example>
*
* Alternatively, use gst_buffer_new_allocate()
* to create a buffer with preallocated data of a given size.
*
* Buffers can contain a list of #GstMemory objects. You can retrieve how many
* memory objects with gst_buffer_n_memory() and you can get a pointer
* to memory with gst_buffer_peek_memory()
*
* A buffer will usually have timestamps, and a duration, but neither of these
* are guaranteed (they may be set to #GST_CLOCK_TIME_NONE). Whenever a
* meaningful value can be given for these, they should be set. The timestamps
* and duration are measured in nanoseconds (they are #GstClockTime values).
*
* A buffer can also have one or both of a start and an end offset. These are
* media-type specific. For video buffers, the start offset will generally be
* the frame number. For audio buffers, it will be the number of samples
* produced so far. For compressed data, it could be the byte offset in a
* source or destination file. Likewise, the end offset will be the offset of
* the end of the buffer. These can only be meaningfully interpreted if you
* know the media type of the buffer (the #GstCaps set on it). Either or both
* can be set to #GST_BUFFER_OFFSET_NONE.
*
* 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_copy_region().
*
* If a plug-in wants to modify the buffer data or metadata in-place, it should
* first obtain a buffer that is safe to modify by using
* gst_buffer_make_writable(). 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 if a certain #GstBufferFlag is set.
*
* Buffers can be efficiently merged into a larger buffer with
* gst_buffer_span(), which avoids memory copies when 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 are usually freed by unreffing them with gst_buffer_unref(). When
* the refcount drops to 0, any data pointed to by the buffer is unreffed as
* well.
*
* Last reviewed on November 8, 2011 (0.11.2)
*/
#include "gst_private.h"
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#ifdef HAVE_STDLIB_H
#include <stdlib.h>
#endif
#include "gstbuffer.h"
#include "gstbufferpool.h"
#include "gstinfo.h"
#include "gstutils.h"
#include "gstminiobject.h"
#include "gstversion.h"
GType _gst_buffer_type = 0;
static GstMemory *_gst_buffer_arr_span (GstMemory ** mem[], gsize len[],
guint n, gsize offset, gsize size, gboolean writable);
typedef struct _GstMetaItem GstMetaItem;
struct _GstMetaItem
{
GstMetaItem *next;
GstMeta meta;
};
#define ITEM_SIZE(info) ((info)->size + sizeof (GstMetaItem))
#define GST_BUFFER_MEM_MAX 16
#define GST_BUFFER_MEM_LEN(b) (((GstBufferImpl *)(b))->len)
#define GST_BUFFER_MEM_ARRAY(b) (((GstBufferImpl *)(b))->mem)
#define GST_BUFFER_MEM_PTR(b,i) (((GstBufferImpl *)(b))->mem[i])
#define GST_BUFFER_BUFMEM(b) (((GstBufferImpl *)(b))->bufmem)
#define GST_BUFFER_META(b) (((GstBufferImpl *)(b))->item)
typedef struct
{
GstBuffer buffer;
/* the memory blocks */
guint len;
GstMemory *mem[GST_BUFFER_MEM_MAX];
/* memory of the buffer when allocated from 1 chunk */
GstMemory *bufmem;
/* FIXME, make metadata allocation more efficient by using part of the
* GstBufferImpl */
GstMetaItem *item;
} GstBufferImpl;
static GstMemory *
_span_memory (GstBuffer * buffer, gsize offset, gsize size, gboolean writable)
{
GstMemory *span, **mem[1];
gsize len[1];
/* not enough room, span buffers */
mem[0] = GST_BUFFER_MEM_ARRAY (buffer);
len[0] = GST_BUFFER_MEM_LEN (buffer);
if (size == -1)
size = gst_buffer_get_size (buffer);
span = _gst_buffer_arr_span (mem, len, 1, offset, size, writable);
return span;
}
static void
_replace_memory (GstBuffer * buffer, GstMemory * mem)
{
gsize len, i;
/* unref old buffers */
len = GST_BUFFER_MEM_LEN (buffer);
for (i = 0; i < len; i++)
gst_memory_unref (GST_BUFFER_MEM_PTR (buffer, i));
/* replace with single spanned buffer */
GST_BUFFER_MEM_PTR (buffer, 0) = mem;
GST_BUFFER_MEM_LEN (buffer) = 1;
}
static inline void
_memory_add (GstBuffer * buffer, guint idx, GstMemory * mem)
{
guint i, len = GST_BUFFER_MEM_LEN (buffer);
if (G_UNLIKELY (len >= GST_BUFFER_MEM_MAX)) {
/* too many buffer, span them. */
/* FIXME, there is room for improvement here: We could only try to merge
* 2 buffers to make some room. If we can't efficiently merge 2 buffers we
* could try to only merge the two smallest buffers to avoid memcpy, etc. */
_replace_memory (buffer, _span_memory (buffer, 0, -1, FALSE));
/* we now have 1 single spanned buffer */
len = 1;
}
if (idx == -1)
idx = len;
for (i = len; i > idx; i--) {
/* move buffers to insert, FIXME, we need to insert first and then merge */
GST_BUFFER_MEM_PTR (buffer, i) = GST_BUFFER_MEM_PTR (buffer, i - 1);
}
/* and insert the new buffer */
GST_BUFFER_MEM_PTR (buffer, idx) = mem;
GST_BUFFER_MEM_LEN (buffer) = len + 1;
}
GST_DEFINE_MINI_OBJECT_TYPE (GstBuffer, gst_buffer);
void
_priv_gst_buffer_initialize (void)
{
_gst_buffer_type = gst_buffer_get_type ();
}
/**
* gst_buffer_copy_into:
* @dest: a destination #GstBuffer
* @src: a source #GstBuffer
* @flags: flags indicating what metadata fields should be copied.
* @offset: offset to copy from
* @size: total size to copy. If -1, all data is copied.
*
* Copies the information from @src into @dest.
*
* @flags indicate which fields will be copied.
*/
void
gst_buffer_copy_into (GstBuffer * dest, GstBuffer * src,
GstBufferCopyFlags flags, gsize offset, gsize size)
{
GstMetaItem *walk;
gsize bufsize;
g_return_if_fail (dest != NULL);
g_return_if_fail (src != NULL);
/* nothing to copy if the buffers are the same */
if (G_UNLIKELY (dest == src))
return;
g_return_if_fail (gst_buffer_is_writable (dest));
bufsize = gst_buffer_get_size (src);
g_return_if_fail (bufsize >= offset);
if (size == -1)
size = bufsize - offset;
g_return_if_fail (bufsize >= offset + size);
GST_CAT_LOG (GST_CAT_BUFFER, "copy %p to %p, offset %" G_GSIZE_FORMAT
"-%" G_GSIZE_FORMAT "/%" G_GSIZE_FORMAT, src, dest, offset, size,
bufsize);
if (flags & GST_BUFFER_COPY_FLAGS) {
/* copy flags */
GST_MINI_OBJECT_FLAGS (dest) = GST_MINI_OBJECT_FLAGS (src);
}
if (flags & GST_BUFFER_COPY_TIMESTAMPS) {
if (offset == 0) {
GST_BUFFER_PTS (dest) = GST_BUFFER_PTS (src);
GST_BUFFER_DTS (dest) = GST_BUFFER_DTS (src);
GST_BUFFER_OFFSET (dest) = GST_BUFFER_OFFSET (src);
if (size == bufsize) {
GST_BUFFER_DURATION (dest) = GST_BUFFER_DURATION (src);
GST_BUFFER_OFFSET_END (dest) = GST_BUFFER_OFFSET_END (src);
}
} else {
GST_BUFFER_PTS (dest) = GST_CLOCK_TIME_NONE;
GST_BUFFER_DTS (dest) = GST_CLOCK_TIME_NONE;
GST_BUFFER_DURATION (dest) = GST_CLOCK_TIME_NONE;
GST_BUFFER_OFFSET (dest) = GST_BUFFER_OFFSET_NONE;
GST_BUFFER_OFFSET_END (dest) = GST_BUFFER_OFFSET_NONE;
}
}
if (flags & GST_BUFFER_COPY_MEMORY) {
GstMemory *mem;
gsize skip, left, len, i, bsize;
len = GST_BUFFER_MEM_LEN (src);
left = size;
skip = offset;
/* copy and make regions of the memory */
for (i = 0; i < len && left > 0; i++) {
mem = GST_BUFFER_MEM_PTR (src, i);
bsize = gst_memory_get_sizes (mem, NULL, NULL);
if (bsize <= skip) {
/* don't copy buffer */
skip -= bsize;
} else {
gsize tocopy;
tocopy = MIN (bsize - skip, left);
if (mem->flags & GST_MEMORY_FLAG_NO_SHARE) {
/* no share, always copy then */
mem = gst_memory_copy (mem, skip, tocopy);
skip = 0;
} else if (tocopy < bsize) {
/* we need to clip something */
mem = gst_memory_share (mem, skip, tocopy);
skip = 0;
} else {
mem = gst_memory_ref (mem);
}
_memory_add (dest, -1, mem);
left -= tocopy;
}
}
if (flags & GST_BUFFER_COPY_MERGE) {
_replace_memory (dest, _span_memory (dest, 0, size, FALSE));
}
}
for (walk = GST_BUFFER_META (src); walk; walk = walk->next) {
GstMeta *meta = &walk->meta;
const GstMetaInfo *info = meta->info;
if (info->copy_func)
info->copy_func (dest, meta, src, offset, size);
}
}
static GstBuffer *
_gst_buffer_copy (GstBuffer * buffer)
{
GstBuffer *copy;
g_return_val_if_fail (buffer != NULL, NULL);
/* create a fresh new buffer */
copy = gst_buffer_new ();
/* we simply copy everything from our parent */
gst_buffer_copy_into (copy, buffer, GST_BUFFER_COPY_ALL, 0, -1);
return copy;
}
/* the default dispose function revives the buffer and returns it to the
* pool when there is a pool */
static gboolean
_gst_buffer_dispose (GstBuffer * buffer)
{
GstBufferPool *pool;
/* no pool, do free */
if ((pool = buffer->pool) == NULL)
return TRUE;
/* keep the buffer alive */
gst_buffer_ref (buffer);
/* return the buffer to the pool */
GST_CAT_LOG (GST_CAT_BUFFER, "release %p to pool %p", buffer, pool);
gst_buffer_pool_release_buffer (pool, buffer);
return FALSE;
}
static void
_gst_buffer_free (GstBuffer * buffer)
{
GstMetaItem *walk, *next;
guint i, len;
gsize msize;
g_return_if_fail (buffer != NULL);
GST_CAT_LOG (GST_CAT_BUFFER, "finalize %p", buffer);
/* free metadata */
for (walk = GST_BUFFER_META (buffer); walk; walk = next) {
GstMeta *meta = &walk->meta;
const GstMetaInfo *info = meta->info;
/* call free_func if any */
if (info->free_func)
info->free_func (meta, buffer);
next = walk->next;
/* and free the slice */
g_slice_free1 (ITEM_SIZE (info), walk);
}
/* get the size, when unreffing the memory, we could also unref the buffer
* itself */
msize = GST_MINI_OBJECT_SIZE (buffer);
/* free our memory */
len = GST_BUFFER_MEM_LEN (buffer);
for (i = 0; i < len; i++)
gst_memory_unref (GST_BUFFER_MEM_PTR (buffer, i));
/* we set msize to 0 when the buffer is part of the memory block */
if (msize)
g_slice_free1 (msize, buffer);
else
gst_memory_unref (GST_BUFFER_BUFMEM (buffer));
}
static void
gst_buffer_init (GstBufferImpl * buffer, gsize size)
{
gst_mini_object_init (GST_MINI_OBJECT_CAST (buffer), _gst_buffer_type, size);
buffer->buffer.mini_object.copy =
(GstMiniObjectCopyFunction) _gst_buffer_copy;
buffer->buffer.mini_object.dispose =
(GstMiniObjectDisposeFunction) _gst_buffer_dispose;
buffer->buffer.mini_object.free =
(GstMiniObjectFreeFunction) _gst_buffer_free;
GST_BUFFER (buffer)->pool = NULL;
GST_BUFFER_PTS (buffer) = GST_CLOCK_TIME_NONE;
GST_BUFFER_DTS (buffer) = GST_CLOCK_TIME_NONE;
GST_BUFFER_DURATION (buffer) = GST_CLOCK_TIME_NONE;
GST_BUFFER_OFFSET (buffer) = GST_BUFFER_OFFSET_NONE;
GST_BUFFER_OFFSET_END (buffer) = GST_BUFFER_OFFSET_NONE;
GST_BUFFER_MEM_LEN (buffer) = 0;
GST_BUFFER_META (buffer) = NULL;
}
/**
* gst_buffer_new:
*
* Creates a newly allocated buffer without any data.
*
* MT safe.
*
* Returns: (transfer full): the new #GstBuffer.
*/
GstBuffer *
gst_buffer_new (void)
{
GstBufferImpl *newbuf;
newbuf = g_slice_new (GstBufferImpl);
GST_CAT_LOG (GST_CAT_BUFFER, "new %p", newbuf);
gst_buffer_init (newbuf, sizeof (GstBufferImpl));
return GST_BUFFER_CAST (newbuf);
}
/**
* gst_buffer_new_allocate:
* @allocator: the #GstAllocator to use
* @size: the size in bytes of the new buffer's data.
* @align: the alignment of the buffer memory
*
* Tries to create a newly allocated buffer with data of the given size and
* alignment from @allocator. If the requested amount of memory can't be
* allocated, NULL will be returned. The allocated buffer memory is not cleared.
*
* When @allocator is NULL, the default memory allocator will be used.
*
* Allocator buffer memory will be aligned to multiples of (@align + 1) bytes.
*
* Note that when @size == 0, the buffer will not have memory associated with it.
*
* MT safe.
*
* Returns: (transfer full): a new #GstBuffer, or NULL if the memory couldn't
* be allocated.
*/
GstBuffer *
gst_buffer_new_allocate (const GstAllocator * allocator, gsize size,
gsize align)
{
GstBuffer *newbuf;
GstMemory *mem;
#if 0
guint8 *data;
gsize asize;
#endif
#if 1
if (size > 0) {
mem = gst_allocator_alloc (allocator, size, align);
if (G_UNLIKELY (mem == NULL))
goto no_memory;
} else {
mem = NULL;
}
newbuf = gst_buffer_new ();
if (mem != NULL)
_memory_add (newbuf, -1, mem);
GST_CAT_LOG (GST_CAT_BUFFER,
"new buffer %p of size %" G_GSIZE_FORMAT " from allocator %p", newbuf,
size, allocator);
#endif
#if 0
asize = sizeof (GstBufferImpl) + size;
data = g_slice_alloc (asize);
if (G_UNLIKELY (data == NULL))
goto no_memory;
newbuf = GST_BUFFER_CAST (data);
gst_buffer_init ((GstBufferImpl *) data, asize);
if (size > 0) {
mem = gst_memory_new_wrapped (0, data + sizeof (GstBufferImpl), NULL,
size, 0, size);
_memory_add (newbuf, -1, mem);
}
#endif
#if 0
/* allocate memory and buffer, it might be interesting to do this but there
* are many complications. We need to keep the memory mapped to access the
* buffer fields and the memory for the buffer might be just very slow. We
* also need to do some more magic to get the alignment right. */
asize = sizeof (GstBufferImpl) + size;
mem = gst_allocator_alloc (allocator, asize, align);
if (G_UNLIKELY (mem == NULL))
goto no_memory;
/* map the data part and init the buffer in it, set the buffer size to 0 so
* that a finalize won't free the buffer */
data = gst_memory_map (mem, &asize, NULL, GST_MAP_WRITE);
gst_buffer_init ((GstBufferImpl *) data, 0);
gst_memory_unmap (mem, data, asize);
/* strip off the buffer */
gst_memory_resize (mem, sizeof (GstBufferImpl), size);
newbuf = GST_BUFFER_CAST (data);
GST_BUFFER_BUFMEM (newbuf) = mem;
if (size > 0)
_memory_add (newbuf, -1, gst_memory_ref (mem));
#endif
return newbuf;
/* ERRORS */
no_memory:
{
GST_CAT_WARNING (GST_CAT_BUFFER,
"failed to allocate %" G_GSIZE_FORMAT " bytes", size);
return NULL;
}
}
/**
* gst_buffer_new_wrapped_full:
* @data: data to wrap
* @free_func: function to free @data
* @offset: offset in @data of valid data
* @size: size of valid data in @data starting at @offset
*
* Creates a new buffer that wraps the given @data. Valid data is set
* to start at @offset and up to @size. If no @free_func is provided,
* buffer memory is marked READONLY.
*
* MT safe.
*
* Returns: (transfer full): a new #GstBuffer
*/
GstBuffer *
gst_buffer_new_wrapped_full (gpointer data, GFreeFunc free_func, gsize offset,
gsize size)
{
GstBuffer *newbuf;
g_return_val_if_fail (offset <= size, NULL);
newbuf = gst_buffer_new ();
gst_buffer_take_memory (newbuf, -1,
gst_memory_new_wrapped (free_func ? 0 : GST_MEMORY_FLAG_READONLY,
data, free_func, offset + size, offset, size));
return newbuf;
}
/**
* gst_buffer_new_wrapped:
* @data: data to wrap
* @size: allocated size of @data
*
* Creates a new buffer that wraps the given @data. The memory will be freed
* with g_free and will be marked writable.
*
* MT safe.
*
* Returns: (transfer full): a new #GstBuffer
*/
GstBuffer *
gst_buffer_new_wrapped (gpointer data, gsize size)
{
return gst_buffer_new_wrapped_full (data, g_free, 0, size);
}
/**
* gst_buffer_n_memory:
* @buffer: a #GstBuffer.
*
* Get the amount of memory blocks that this buffer has.
*
* Returns: (transfer full): the amount of memory block in this buffer.
*/
guint
gst_buffer_n_memory (GstBuffer * buffer)
{
g_return_val_if_fail (GST_IS_BUFFER (buffer), 0);
return GST_BUFFER_MEM_LEN (buffer);
}
/**
* gst_buffer_take_memory:
* @buffer: a #GstBuffer.
* @idx: the index to add the memory at, or -1 to append it to the end
* @mem: (transfer full): a #GstMemory.
*
* Add the memory block @mem to @buffer at @idx. This function takes ownership
* of @mem and thus doesn't increase its refcount.
*/
void
gst_buffer_take_memory (GstBuffer * buffer, gint idx, GstMemory * mem)
{
g_return_if_fail (GST_IS_BUFFER (buffer));
g_return_if_fail (gst_buffer_is_writable (buffer));
g_return_if_fail (mem != NULL);
g_return_if_fail (idx == -1 ||
(idx >= 0 && idx <= GST_BUFFER_MEM_LEN (buffer)));
_memory_add (buffer, idx, mem);
}
static GstMemory *
_get_memory (GstBuffer * buffer, guint idx, gboolean write)
{
GstMemory *mem;
mem = GST_BUFFER_MEM_PTR (buffer, idx);
if (G_UNLIKELY (write && !GST_MEMORY_IS_WRITABLE (mem))) {
GstMemory *copy;
GST_CAT_LOG (GST_CAT_BUFFER,
"making writable copy of memory %p in buffer %p", mem, buffer);
/* replace with a writable copy */
copy = gst_memory_copy (mem, 0, -1);
GST_BUFFER_MEM_PTR (buffer, idx) = copy;
gst_memory_unref (mem);
mem = copy;
}
return mem;
}
/**
* gst_buffer_peek_memory:
* @buffer: a #GstBuffer.
* @idx: an index
* @flags: #GstMapFlags
*
* Get the memory block in @buffer at @idx for memory access in @flags.
* This function does not return a refcount to the memory block. The memory
* block stays valid for as long as the caller has a valid reference to @buffer.
*
* @buffer should be writable when @flags contains #GST_MAP_WRITE. If the memory
* at @idx is not writable, a new writable copy will be installed in @buffer and
* returned.
*
* Returns: a #GstMemory at @idx.
*/
GstMemory *
gst_buffer_peek_memory (GstBuffer * buffer, guint idx, GstMapFlags flags)
{
GstMemory *mem;
gboolean write;
write = (flags & GST_MAP_WRITE) != 0;
g_return_val_if_fail (GST_IS_BUFFER (buffer), NULL);
g_return_val_if_fail (idx < GST_BUFFER_MEM_LEN (buffer), NULL);
/* check if we can write when asked for write access */
if (G_UNLIKELY (write && !gst_buffer_is_writable (buffer)))
goto not_writable;
mem = _get_memory (buffer, idx, write);
return mem;
/* ERRORS */
not_writable:
{
g_return_val_if_fail (gst_buffer_is_writable (buffer), NULL);
return NULL;
}
}
/**
* gst_buffer_remove_memory_range:
* @buffer: a #GstBuffer.
* @idx: an index
* @length: a length
*
* Remove @len memory blocks in @buffer starting from @idx.
*
* @length can be -1, in which case all memory starting from @idx is removed.
*/
void
gst_buffer_remove_memory_range (GstBuffer * buffer, guint idx, guint length)
{
guint len, i, end;
g_return_if_fail (GST_IS_BUFFER (buffer));
g_return_if_fail (gst_buffer_is_writable (buffer));
len = GST_BUFFER_MEM_LEN (buffer);
if (length == -1) {
g_return_if_fail (idx < len);
length = len - idx;
}
end = idx + length;
for (i = idx; i < end; i++)
gst_memory_unref (GST_BUFFER_MEM_PTR (buffer, i));
if (end != len) {
g_memmove (&GST_BUFFER_MEM_PTR (buffer, idx),
&GST_BUFFER_MEM_PTR (buffer, end), (len - end) * sizeof (gpointer));
}
GST_BUFFER_MEM_LEN (buffer) = len - length;
}
/**
* gst_buffer_get_sizes:
* @buffer: a #GstBuffer.
* @offset: a pointer to the offset
* @maxsize: a pointer to the maxsize
*
* Get the total size of all memory blocks in @buffer.
*
* When not %NULL, @offset will contain the offset of the data in the first
* memory block in @buffer and @maxsize will contain the sum of the size
* and @offset and the amount of extra padding on the last memory block.
* @offset and @maxsize can be used to resize the buffer with
* gst_buffer_resize().
*
* Returns: the total size of the memory in @buffer.
*/
gsize
gst_buffer_get_sizes (GstBuffer * buffer, gsize * offset, gsize * maxsize)
{
guint len;
gsize size;
GstMemory *mem;
g_return_val_if_fail (GST_IS_BUFFER (buffer), 0);
len = GST_BUFFER_MEM_LEN (buffer);
if (G_LIKELY (len == 1)) {
/* common case */
mem = GST_BUFFER_MEM_PTR (buffer, 0);
size = gst_memory_get_sizes (mem, offset, maxsize);
} else {
guint i;
gsize extra, offs;
size = offs = extra = 0;
for (i = 0; i < len; i++) {
gsize s, o, ms;
mem = GST_BUFFER_MEM_PTR (buffer, i);
s = gst_memory_get_sizes (mem, &o, &ms);
if (s) {
if (size == 0)
/* first size, take accumulated data before as the offset */
offs = extra + o;
/* add sizes */
size += s;
/* save the amount of data after this block */
extra = ms - (o + s);
} else {
/* empty block, add as extra */
extra += ms;
}
}
if (offset)
*offset = offs;
if (maxsize)
*maxsize = offs + size + extra;
}
return size;
}
/**
* gst_buffer_resize:
* @buffer: a #GstBuffer.
* @offset: the offset adjustement
* @size: the new size
*
* Set the total size of the buffer
*/
void
gst_buffer_resize (GstBuffer * buffer, gssize offset, gsize size)
{
guint len;
guint i;
gsize bsize, bufsize, bufoffs, bufmax;
GstMemory *mem;
g_return_if_fail (gst_buffer_is_writable (buffer));
bufsize = gst_buffer_get_sizes (buffer, &bufoffs, &bufmax);
GST_CAT_LOG (GST_CAT_BUFFER, "trim %p %" G_GSSIZE_FORMAT "-%" G_GSIZE_FORMAT
" size:%" G_GSIZE_FORMAT " offs:%" G_GSIZE_FORMAT " max:%" G_GSIZE_FORMAT,
buffer, offset, size, bufsize, bufoffs, bufmax);
/* we can't go back further than the current offset or past the end of the
* buffer */
g_return_if_fail ((offset < 0 && bufoffs >= -offset) || (offset >= 0
&& bufoffs + offset <= bufmax));
if (size == -1) {
g_return_if_fail (bufsize >= offset);
size = bufsize - offset;
}
g_return_if_fail (bufmax >= bufoffs + offset + size);
len = GST_BUFFER_MEM_LEN (buffer);
/* copy and trim */
for (i = 0; i < len; i++) {
gsize left, noffs;
mem = GST_BUFFER_MEM_PTR (buffer, i);
bsize = gst_memory_get_sizes (mem, NULL, NULL);
noffs = 0;
/* last buffer always gets resized to the remaining size */
if (i + 1 == len)
left = size;
/* shrink buffers before the offset */
else if ((gssize) bsize <= offset) {
left = 0;
noffs = offset - bsize;
offset = 0;
}
/* clip other buffers */
else
left = MIN (bsize - offset, size);
if (offset != 0 || left != bsize) {
/* we need to clip something */
if (GST_MEMORY_IS_WRITABLE (mem)) {
gst_memory_resize (mem, offset, left);
} else {
GstMemory *tmp;
if (mem->flags & GST_MEMORY_FLAG_NO_SHARE)
tmp = gst_memory_copy (mem, offset, left);
else
tmp = gst_memory_share (mem, offset, left);
gst_memory_unref (mem);
mem = tmp;
}
}
offset = noffs;
size -= left;
GST_BUFFER_MEM_PTR (buffer, i) = mem;
}
}
/**
* gst_buffer_map:
* @buffer: a #GstBuffer.
* @size: a location for the size
* @maxsize: a location for the max size
* @flags: flags for the mapping
*
* This function return a pointer to the memory in @buffer. @flags describe the
* desired access of the memory. When @flags is #GST_MAP_WRITE, @buffer should
* be writable (as returned from gst_buffer_is_writable()).
*
* @size and @maxsize will contain the current valid number of bytes in the
* returned memory area and the total maximum mount of bytes available in the
* returned memory area respectively. Both parameters can be %NULL.
*
* When @buffer is writable but the memory isn't, a writable copy will
* automatically be created and returned. The readonly copy of the buffer memory
* will then also be replaced with this writable copy.
*
* When the buffer contains multiple memory blocks, the returned pointer will be
* a concatenation of the memory blocks.
*
* Returns: a pointer to the memory for the buffer.
*/
gpointer
gst_buffer_map (GstBuffer * buffer, gsize * size, gsize * maxsize,
GstMapFlags flags)
{
guint len;
gpointer data;
GstMemory *mem;
gboolean write, writable;
g_return_val_if_fail (GST_IS_BUFFER (buffer), NULL);
write = (flags & GST_MAP_WRITE) != 0;
writable = gst_buffer_is_writable (buffer);
/* check if we can write when asked for write access */
if (G_UNLIKELY (write && !writable))
goto not_writable;
len = GST_BUFFER_MEM_LEN (buffer);
if (G_UNLIKELY (len == 0)) {
/* no memory, return immediately */
if (size)
*size = 0;
if (maxsize)
*maxsize = 0;
return NULL;
}
if (G_LIKELY (len == 1)) {
/* we can take the first one */
mem = GST_BUFFER_MEM_PTR (buffer, 0);
} else {
/* we need to span memory */
if (writable) {
/* if we can write, we can change the memory with the spanned
* memory */
mem = _span_memory (buffer, 0, -1, write);
_replace_memory (buffer, mem);
} else {
gsize bsize;
/* extract all data in new memory, FIXME slow!! */
bsize = gst_buffer_get_size (buffer);
data = g_malloc (bsize);
gst_buffer_extract (buffer, 0, data, bsize);
if (size)
*size = bsize;
if (maxsize)
*maxsize = bsize;
return data;
}
}
if (G_UNLIKELY (write && !GST_MEMORY_IS_WRITABLE (mem))) {
GstMemory *copy;
/* replace with a writable copy */
copy = gst_memory_copy (mem, 0, -1);
GST_BUFFER_MEM_PTR (buffer, 0) = copy;
gst_memory_unref (mem);
mem = copy;
}
data = gst_memory_map (mem, size, maxsize, flags);
return data;
/* ERROR */
not_writable:
{
g_return_val_if_fail (gst_buffer_is_writable (buffer), NULL);
return NULL;
}
}
/**
* gst_buffer_unmap:
* @buffer: a #GstBuffer.
* @data: the previously mapped data
* @size: the size of @data
*
* Release the memory previously mapped with gst_buffer_map(). Pass -1 to size
* if no update is needed.
*
* Returns: #TRUE on success. #FALSE can be returned when the new size is larger
* than the maxsize of the memory.
*/
gboolean
gst_buffer_unmap (GstBuffer * buffer, gpointer data, gsize size)
{
gboolean result;
guint len;
g_return_val_if_fail (GST_IS_BUFFER (buffer), FALSE);
len = GST_BUFFER_MEM_LEN (buffer);
if (G_LIKELY (len == 1)) {
GstMemory *mem = GST_BUFFER_MEM_PTR (buffer, 0);
result = gst_memory_unmap (mem, data, size);
} else {
/* this must have been from read-only access. After _map, the buffer either
* only contains 1 memory block or it allocated memory to join memory
* blocks. It's not allowed to add buffers between _map and _unmap. */
g_free (data);
result = TRUE;
}
return result;
}
/**
* gst_buffer_fill:
* @buffer: a #GstBuffer.
* @offset: the offset to fill
* @src: the source address
* @size: the size to fill
*
* Copy @size bytes from @src to @buffer at @offset.
*
* Returns: The amount of bytes copied. This value can be lower than @size
* when @buffer did not contain enough data.
*/
gsize
gst_buffer_fill (GstBuffer * buffer, gsize offset, gconstpointer src,
gsize size)
{
gsize i, len, left;
const guint8 *ptr = src;
g_return_val_if_fail (GST_IS_BUFFER (buffer), 0);
g_return_val_if_fail (gst_buffer_is_writable (buffer), 0);
g_return_val_if_fail (src != NULL, 0);
len = GST_BUFFER_MEM_LEN (buffer);
left = size;
for (i = 0; i < len && left > 0; i++) {
guint8 *data;
gsize ssize, tocopy;
GstMemory *mem;
mem = _get_memory (buffer, i, TRUE);
data = gst_memory_map (mem, &ssize, NULL, GST_MAP_WRITE);
if (ssize > offset) {
/* we have enough */
tocopy = MIN (ssize - offset, left);
memcpy (data + offset, ptr, tocopy);
left -= tocopy;
ptr += tocopy;
offset = 0;
} else {
/* offset past buffer, skip */
offset -= ssize;
}
gst_memory_unmap (mem, data, ssize);
}
return size - left;
}
/**
* gst_buffer_extract:
* @buffer: a #GstBuffer.
* @offset: the offset to extract
* @dest: the destination address
* @size: the size to extract
*
* Copy @size bytes starting from @offset in @buffer to @dest.
*
* Returns: The amount of bytes extracted. This value can be lower than @size
* when @buffer did not contain enough data.
*/
gsize
gst_buffer_extract (GstBuffer * buffer, gsize offset, gpointer dest, gsize size)
{
gsize i, len, left;
guint8 *ptr = dest;
g_return_val_if_fail (GST_IS_BUFFER (buffer), 0);
g_return_val_if_fail (dest != NULL, 0);
len = GST_BUFFER_MEM_LEN (buffer);
left = size;
for (i = 0; i < len && left > 0; i++) {
guint8 *data;
gsize ssize, tocopy;
GstMemory *mem;
mem = GST_BUFFER_MEM_PTR (buffer, i);
data = gst_memory_map (mem, &ssize, NULL, GST_MAP_READ);
if (ssize > offset) {
/* we have enough */
tocopy = MIN (ssize - offset, left);
memcpy (ptr, data + offset, tocopy);
left -= tocopy;
ptr += tocopy;
offset = 0;
} else {
/* offset past buffer, skip */
offset -= ssize;
}
gst_memory_unmap (mem, data, ssize);
}
return size - left;
}
/**
* gst_buffer_memcmp:
* @buffer: a #GstBuffer.
* @offset: the offset in @buffer
* @mem: the memory to compare
* @size: the size to compare
*
* Compare @size bytes starting from @offset in @buffer with the memory in @mem.
*
* Returns: 0 if the memory is equal.
*/
gint
gst_buffer_memcmp (GstBuffer * buffer, gsize offset, gconstpointer mem,
gsize size)
{
gsize i, len;
const guint8 *ptr = mem;
gint res = 0;
g_return_val_if_fail (GST_IS_BUFFER (buffer), 0);
g_return_val_if_fail (mem != NULL, 0);
len = GST_BUFFER_MEM_LEN (buffer);
for (i = 0; i < len && size > 0 && res == 0; i++) {
guint8 *data;
gsize ssize, tocmp;
GstMemory *mem;
mem = GST_BUFFER_MEM_PTR (buffer, i);
data = gst_memory_map (mem, &ssize, NULL, GST_MAP_READ);
if (ssize > offset) {
/* we have enough */
tocmp = MIN (ssize - offset, size);
res = memcmp (ptr, data + offset, tocmp);
size -= tocmp;
ptr += tocmp;
offset = 0;
} else {
/* offset past buffer, skip */
offset -= ssize;
}
gst_memory_unmap (mem, data, ssize);
}
return res;
}
/**
* gst_buffer_memset:
* @buffer: a #GstBuffer.
* @offset: the offset in @buffer
* @val: the value to set
* @size: the size to set
*
* Fill @buf with @size bytes with @val starting from @offset.
*
* Returns: The amount of bytes filled. This value can be lower than @size
* when @buffer did not contain enough data.
*/
gsize
gst_buffer_memset (GstBuffer * buffer, gsize offset, guint8 val, gsize size)
{
gsize i, len, left;
g_return_val_if_fail (GST_IS_BUFFER (buffer), 0);
g_return_val_if_fail (gst_buffer_is_writable (buffer), 0);
len = GST_BUFFER_MEM_LEN (buffer);
left = size;
for (i = 0; i < len && left > 0; i++) {
guint8 *data;
gsize ssize, toset;
GstMemory *mem;
mem = GST_BUFFER_MEM_PTR (buffer, i);
data = gst_memory_map (mem, &ssize, NULL, GST_MAP_WRITE);
if (ssize > offset) {
/* we have enough */
toset = MIN (ssize - offset, left);
memset (data + offset, val, toset);
left -= toset;
offset = 0;
} else {
/* offset past buffer, skip */
offset -= ssize;
}
gst_memory_unmap (mem, data, ssize);
}
return size - left;
}
/**
* gst_buffer_copy_region:
* @parent: a #GstBuffer.
* @flags: the #GstBufferCopyFlags
* @offset: the offset into parent #GstBuffer at which the new sub-buffer
* begins.
* @size: the size of the new #GstBuffer sub-buffer, in bytes.
*
* Creates a sub-buffer from @parent at @offset and @size.
* This sub-buffer uses the actual memory space of the parent buffer.
* This function will copy the offset and timestamp fields when the
* offset is 0. If not, they will be set to #GST_CLOCK_TIME_NONE and
* #GST_BUFFER_OFFSET_NONE.
* If @offset equals 0 and @size equals the total size of @buffer, the
* duration and offset end fields are also copied. If not they will be set
* to #GST_CLOCK_TIME_NONE and #GST_BUFFER_OFFSET_NONE.
*
* MT safe.
*
* Returns: (transfer full): the new #GstBuffer or NULL if the arguments were
* invalid.
*/
GstBuffer *
gst_buffer_copy_region (GstBuffer * buffer, GstBufferCopyFlags flags,
gsize offset, gsize size)
{
GstBuffer *copy;
g_return_val_if_fail (buffer != NULL, NULL);
/* create the new buffer */
copy = gst_buffer_new ();
GST_CAT_LOG (GST_CAT_BUFFER, "new region copy %p of %p %" G_GSIZE_FORMAT
"-%" G_GSIZE_FORMAT, copy, buffer, offset, size);
gst_buffer_copy_into (copy, buffer, flags, offset, size);
return copy;
}
static gboolean
_gst_buffer_arr_is_span_fast (GstMemory ** mem[], gsize len[], guint n,
gsize * offset, GstMemory ** parent)
{
GstMemory *mcur, *mprv;
gboolean have_offset = FALSE;
guint count, i;
mcur = mprv = NULL;
for (count = 0; count < n; count++) {
gsize offs, clen;
GstMemory **cmem;
cmem = mem[count];
clen = len[count];
for (i = 0; i < clen; i++) {
if (mcur)
mprv = mcur;
mcur = cmem[i];
if (mprv && mcur) {
/* check is memory is contiguous */
if (!gst_memory_is_span (mprv, mcur, &offs))
return FALSE;
if (!have_offset) {
if (offset)
*offset = offs;
if (parent)
*parent = mprv->parent;
have_offset = TRUE;
}
}
}
}
return have_offset;
}
static GstMemory *
_gst_buffer_arr_span (GstMemory ** mem[], gsize len[], guint n, gsize offset,
gsize size, gboolean writable)
{
GstMemory *span, *parent = NULL;
gsize poffset = 0;
if (!writable
&& _gst_buffer_arr_is_span_fast (mem, len, n, &poffset, &parent)) {
if (parent->flags & GST_MEMORY_FLAG_NO_SHARE)
span = gst_memory_copy (parent, offset + poffset, size);
else
span = gst_memory_share (parent, offset + poffset, size);
} else {
gsize count, left;
guint8 *dest, *ptr;
span = gst_allocator_alloc (NULL, size, 0);
dest = gst_memory_map (span, NULL, NULL, GST_MAP_WRITE);
ptr = dest;
left = size;
for (count = 0; count < n; count++) {
gsize i, tocopy, clen, ssize;
guint8 *src;
GstMemory **cmem;
cmem = mem[count];
clen = len[count];
for (i = 0; i < clen && left > 0; i++) {
src = gst_memory_map (cmem[i], &ssize, NULL, GST_MAP_READ);
tocopy = MIN (ssize, left);
if (tocopy > offset) {
memcpy (ptr, src + offset, tocopy - offset);
left -= tocopy;
ptr += tocopy;
offset = 0;
} else {
offset -= tocopy;
}
gst_memory_unmap (cmem[i], src, ssize);
}
}
gst_memory_unmap (span, dest, size);
}
return span;
}
/**
* gst_buffer_is_span_fast:
* @buf1: the first #GstBuffer.
* @buf2: the second #GstBuffer.
*
* Determines whether a gst_buffer_span() can be done without copying
* the contents, that is, whether the data areas are contiguous sub-buffers of
* the same buffer.
*
* MT safe.
* Returns: TRUE if the buffers are contiguous,
* FALSE if a copy would be required.
*/
gboolean
gst_buffer_is_span_fast (GstBuffer * buf1, GstBuffer * buf2)
{
GstMemory **mem[2];
gsize len[2];
g_return_val_if_fail (GST_IS_BUFFER (buf1), FALSE);
g_return_val_if_fail (GST_IS_BUFFER (buf2), FALSE);
g_return_val_if_fail (buf1->mini_object.refcount > 0, FALSE);
g_return_val_if_fail (buf2->mini_object.refcount > 0, FALSE);
mem[0] = GST_BUFFER_MEM_ARRAY (buf1);
len[0] = GST_BUFFER_MEM_LEN (buf1);
mem[1] = GST_BUFFER_MEM_ARRAY (buf2);
len[1] = GST_BUFFER_MEM_LEN (buf2);
return _gst_buffer_arr_is_span_fast (mem, len, 2, NULL, NULL);
}
/**
* gst_buffer_span:
* @buf1: the first source #GstBuffer to merge.
* @offset: the offset in the first buffer from where the new
* buffer should start.
* @buf2: the second source #GstBuffer to merge.
* @size: the total size of the new buffer.
*
* Creates a new buffer that consists of part of buf1 and buf2.
* Logically, buf1 and buf2 are concatenated into a single larger
* buffer, and a new buffer is created at the given offset inside
* this space, with a given length.
*
* If the two source buffers are children of the same larger buffer,
* and are contiguous, the new buffer will be a child of the shared
* parent, and thus no copying is necessary. you can use
* gst_buffer_is_span_fast() to determine if a memcpy will be needed.
*
* MT safe.
*
* Returns: (transfer full): the new #GstBuffer that spans the two source
* buffers, or NULL if the arguments are invalid.
*/
GstBuffer *
gst_buffer_span (GstBuffer * buf1, gsize offset, GstBuffer * buf2, gsize size)
{
GstBuffer *newbuf;
GstMemory *span;
GstMemory **mem[2];
gsize len[2], len1, len2;
g_return_val_if_fail (GST_IS_BUFFER (buf1), NULL);
g_return_val_if_fail (GST_IS_BUFFER (buf2), NULL);
g_return_val_if_fail (buf1->mini_object.refcount > 0, NULL);
g_return_val_if_fail (buf2->mini_object.refcount > 0, NULL);
len1 = gst_buffer_get_size (buf1);
len2 = gst_buffer_get_size (buf2);
g_return_val_if_fail (len1 + len2 > offset, NULL);
if (size == -1)
size = len1 + len2 - offset;
else
g_return_val_if_fail (size <= len1 + len2 - offset, NULL);
mem[0] = GST_BUFFER_MEM_ARRAY (buf1);
len[0] = GST_BUFFER_MEM_LEN (buf1);
mem[1] = GST_BUFFER_MEM_ARRAY (buf2);
len[1] = GST_BUFFER_MEM_LEN (buf2);
span = _gst_buffer_arr_span (mem, len, 2, offset, size, FALSE);
newbuf = gst_buffer_new ();
_memory_add (newbuf, -1, span);
#if 0
/* if the offset is 0, the new buffer has the same timestamp as buf1 */
if (offset == 0) {
GST_BUFFER_OFFSET (newbuf) = GST_BUFFER_OFFSET (buf1);
GST_BUFFER_PTS (newbuf) = GST_BUFFER_PTS (buf1);
GST_BUFFER_DTS (newbuf) = GST_BUFFER_DTS (buf1);
/* if we completely merged the two buffers (appended), we can
* calculate the duration too. Also make sure we's not messing with
* invalid DURATIONS */
if (buf1->size + buf2->size == len) {
if (GST_BUFFER_DURATION_IS_VALID (buf1) &&
GST_BUFFER_DURATION_IS_VALID (buf2)) {
/* add duration */
GST_BUFFER_DURATION (newbuf) = GST_BUFFER_DURATION (buf1) +
GST_BUFFER_DURATION (buf2);
}
if (GST_BUFFER_OFFSET_END_IS_VALID (buf2)) {
/* add offset_end */
GST_BUFFER_OFFSET_END (newbuf) = GST_BUFFER_OFFSET_END (buf2);
}
}
}
#endif
return newbuf;
}
/**
* gst_buffer_get_meta:
* @buffer: a #GstBuffer
* @info: a #GstMetaInfo
*
* Get the metadata for the api in @info on buffer. When there is no such
* metadata, NULL is returned.
*
* Note that the result metadata might not be of the implementation @info.
*
* Returns: the metadata for the api in @info on @buffer.
*/
GstMeta *
gst_buffer_get_meta (GstBuffer * buffer, const GstMetaInfo * info)
{
GstMetaItem *item;
GstMeta *result = NULL;
g_return_val_if_fail (buffer != NULL, NULL);
g_return_val_if_fail (info != NULL, NULL);
/* find GstMeta of the requested API */
for (item = GST_BUFFER_META (buffer); item; item = item->next) {
GstMeta *meta = &item->meta;
if (meta->info->api == info->api) {
result = meta;
break;
}
}
return result;
}
/**
* gst_buffer_add_meta:
* @buffer: a #GstBuffer
* @info: a #GstMetaInfo
* @params: params for @info
*
* Add metadata for @info to @buffer using the parameters in @params.
*
* Returns: the metadata for the api in @info on @buffer.
*/
GstMeta *
gst_buffer_add_meta (GstBuffer * buffer, const GstMetaInfo * info,
gpointer params)
{
GstMetaItem *item;
GstMeta *result = NULL;
gsize size;
g_return_val_if_fail (buffer != NULL, NULL);
g_return_val_if_fail (info != NULL, NULL);
/* create a new slice */
GST_CAT_DEBUG (GST_CAT_BUFFER, "alloc metadata %s of size %" G_GSIZE_FORMAT,
g_type_name (info->type), info->size);
size = ITEM_SIZE (info);
item = g_slice_alloc (size);
result = &item->meta;
result->info = info;
/* call the init_func when needed */
if (info->init_func)
if (!info->init_func (result, params, buffer))
goto init_failed;
/* and add to the list of metadata */
item->next = GST_BUFFER_META (buffer);
GST_BUFFER_META (buffer) = item;
return result;
init_failed:
{
g_slice_free1 (size, item);
return NULL;
}
}
/**
* gst_buffer_remove_meta:
* @buffer: a #GstBuffer
* @meta: a #GstMeta
*
* Remove the metadata for @meta on @buffer.
*
* Returns: %TRUE if the metadata existed and was removed, %FALSE if no such
* metadata was on @buffer.
*/
gboolean
gst_buffer_remove_meta (GstBuffer * buffer, GstMeta * meta)
{
GstMetaItem *walk, *prev;
g_return_val_if_fail (buffer != NULL, FALSE);
g_return_val_if_fail (meta != NULL, FALSE);
/* find the metadata and delete */
prev = GST_BUFFER_META (buffer);
for (walk = prev; walk; walk = walk->next) {
GstMeta *m = &walk->meta;
if (m == meta) {
const GstMetaInfo *info = meta->info;
/* remove from list */
if (GST_BUFFER_META (buffer) == walk)
GST_BUFFER_META (buffer) = walk->next;
else
prev->next = walk->next;
/* call free_func if any */
if (info->free_func)
info->free_func (m, buffer);
/* and free the slice */
g_slice_free1 (ITEM_SIZE (info), walk);
break;
}
prev = walk;
}
return walk != NULL;
}
/**
* gst_buffer_iterate_meta:
* @buffer: a #GstBuffer
* @state: an opaque state pointer
*
* Retrieve the next #GstMeta after @current. If @state points
* to %NULL, the first metadata is returned.
*
* @state will be updated with an opage state pointer
*
* Returns: The next #GstMeta or %NULL when there are no more items.
*/
GstMeta *
gst_buffer_iterate_meta (GstBuffer * buffer, gpointer * state)
{
GstMetaItem **meta;
g_return_val_if_fail (buffer != NULL, NULL);
g_return_val_if_fail (state != NULL, NULL);
meta = (GstMetaItem **) state;
if (*meta == NULL)
/* state NULL, move to first item */
*meta = GST_BUFFER_META (buffer);
else
/* state !NULL, move to next item in list */
*meta = (*meta)->next;
if (*meta)
return &(*meta)->meta;
else
return NULL;
}