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GStreamer 0.10 Core Reference Manual | ![]() |
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#include <gst/gst.h> GstBuffer; enum GstBufferFlag; enum GstBufferCopyFlags; #define GST_BUFFER_FLAGS (buf) #define GST_BUFFER_FLAG_IS_SET (buf,flag) #define GST_BUFFER_FLAG_SET (buf,flag) #define GST_BUFFER_FLAG_UNSET (buf,flag) #define GST_BUFFER_DATA (buf) #define GST_BUFFER_MALLOCDATA (buf) #define GST_BUFFER_FREE_FUNC (buf) #define GST_BUFFER_SIZE (buf) #define GST_BUFFER_TIMESTAMP (buf) #define GST_BUFFER_DURATION (buf) #define GST_BUFFER_CAPS (buf) #define GST_BUFFER_OFFSET (buf) #define GST_BUFFER_OFFSET_END (buf) #define GST_BUFFER_OFFSET_NONE #define GST_BUFFER_DURATION_IS_VALID (buffer) #define GST_BUFFER_TIMESTAMP_IS_VALID (buffer) #define GST_BUFFER_OFFSET_IS_VALID (buffer) #define GST_BUFFER_OFFSET_END_IS_VALID (buffer) #define GST_BUFFER_IS_DISCONT (buffer) #define GST_BUFFER_TRACE_NAME GstBuffer* gst_buffer_new (void); GstBuffer* gst_buffer_new_and_alloc (guint size); GstBuffer* gst_buffer_try_new_and_alloc (guint size); GstBuffer* gst_buffer_ref (GstBuffer *buf); void gst_buffer_unref (GstBuffer *buf); #define gst_buffer_set_data (buf, data, size) GstBuffer* gst_buffer_copy (const GstBuffer *buf); #define GST_BUFFER_COPY_ALL void gst_buffer_copy_metadata (GstBuffer *dest, const GstBuffer *src, GstBufferCopyFlags flags); #define gst_buffer_is_writable (buf) #define gst_buffer_make_writable (buf) gboolean gst_buffer_is_metadata_writable (GstBuffer *buf); GstBuffer* gst_buffer_make_metadata_writable (GstBuffer *buf); #define gst_buffer_replace (obuf,nbuf) GstCaps* gst_buffer_get_caps (GstBuffer *buffer); void gst_buffer_set_caps (GstBuffer *buffer, GstCaps *caps); GstBuffer* gst_buffer_create_sub (GstBuffer *parent, guint offset, guint size); gboolean gst_buffer_is_span_fast (GstBuffer *buf1, GstBuffer *buf2); GstBuffer* gst_buffer_span (GstBuffer *buf1, guint32 offset, GstBuffer *buf2, guint32 len); void gst_buffer_stamp (GstBuffer *dest, const GstBuffer *src); GstBuffer* gst_buffer_join (GstBuffer *buf1, GstBuffer *buf2); GstBuffer* gst_buffer_merge (GstBuffer *buf1, GstBuffer *buf2);
Buffers are the basic unit of data transfer in GStreamer. The GstBuffer type provides all the state necessary to define a region of memory as part of a stream. Sub-buffers 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 set the size of the
buffer data. The following example creates a buffer that can hold a given
video frame with a given width, height and bits per plane.
Example 3. Creating a buffer for a video frame
GstBuffer *buffer; gint size, width, height, bpp; ... size = width * height * bpp; buffer = gst_buffer_new (); GST_BUFFER_SIZE (buffer) = size; GST_BUFFER_MALLOCDATA (buffer) = g_malloc (size); GST_BUFFER_DATA (buffer) = GST_BUFFER_MALLOCDATA (buffer); ...
Alternatively, use gst_buffer_new_and_alloc()
to create a buffer with preallocated data of a given size.
The data pointed to by the buffer can be retrieved with the GST_BUFFER_DATA()
macro. The size of the data can be found with GST_BUFFER_SIZE()
. For buffers
of size 0, the data pointer is undefined (usually NULL) and should never be used.
If an element knows what pad you will push the buffer out on, it should use
gst_pad_alloc_buffer()
instead to create a buffer. This allows downstream
elements to provide special buffers to write in, like hardware buffers.
A buffer has a pointer to a GstCaps describing the media type of the data
in the buffer. Attach caps to the buffer with gst_buffer_set_caps()
; this
is typically done before pushing out a buffer using gst_pad_push()
so that
the downstream element knows the type of the buffer.
A buffer will usually have a timestamp, 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 timestamp 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_create_sub()
.
If a plug-in wants to modify the buffer data 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.
A plugin that only wishes to modify the metadata of a buffer, such as the
offset, timestamp or caps, should use gst_buffer_make_metadata_writable()
,
which will create a subbuffer of the original buffer to ensure the caller
has sole ownership, and not copy the buffer data.
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_merge()
and gst_buffer_span()
if 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 GST_BUFFER_MALLOCDATA()
will
also be freed.
Last reviewed on August 11th, 2006 (0.10.10)
typedef struct { GstMiniObject mini_object; /* pointer to data and its size */ guint8 *data; guint size; /* timestamp */ GstClockTime timestamp; GstClockTime duration; /* the media type of this buffer */ GstCaps *caps; /* media specific offset */ guint64 offset; guint64 offset_end; guint8 *malloc_data; GFreeFunc free_func; } GstBuffer;
The structure of a GstBuffer. Use the associated macros to access the public variables.
GstMiniObject mini_object ; |
the parent structure |
guint8 *data ; |
pointer to the buffer data |
guint size ; |
size of buffer data |
GstClockTime timestamp ; |
timestamp of the buffer, can be GST_CLOCK_TIME_NONE when the timestamp is not known or relevant. |
GstClockTime duration ; |
duration in time of the buffer data, can be GST_CLOCK_TIME_NONE when the duration is not known or relevant. |
GstCaps *caps ; |
the GstCaps describing the data format in this buffer |
guint64 offset ; |
a media specific offset for the buffer data. For video frames, this is the frame number of this buffer. For audio samples, this is the offset of the first sample in this buffer. For file data or compressed data this is the byte offset of the first byte in this buffer. |
guint64 offset_end ; |
the last offset contained in this buffer. It has the same
format as offset .
|
guint8 *malloc_data ; |
a pointer to the allocated memory associated with this buffer.
When the buffer is freed, this data will freed with free_func .
|
GFreeFunc free_func ; |
a custom function that will be called with malloc_data , defaults
to g_free() . Since 0.10.22.
|
typedef enum { GST_BUFFER_FLAG_READONLY = GST_MINI_OBJECT_FLAG_READONLY, GST_BUFFER_FLAG_PREROLL = (GST_MINI_OBJECT_FLAG_LAST << 0), GST_BUFFER_FLAG_DISCONT = (GST_MINI_OBJECT_FLAG_LAST << 1), GST_BUFFER_FLAG_IN_CAPS = (GST_MINI_OBJECT_FLAG_LAST << 2), GST_BUFFER_FLAG_GAP = (GST_MINI_OBJECT_FLAG_LAST << 3), GST_BUFFER_FLAG_DELTA_UNIT = (GST_MINI_OBJECT_FLAG_LAST << 4), GST_BUFFER_FLAG_MEDIA1 = (GST_MINI_OBJECT_FLAG_LAST << 5), GST_BUFFER_FLAG_MEDIA2 = (GST_MINI_OBJECT_FLAG_LAST << 6), GST_BUFFER_FLAG_MEDIA3 = (GST_MINI_OBJECT_FLAG_LAST << 7), GST_BUFFER_FLAG_LAST = (GST_MINI_OBJECT_FLAG_LAST << 8) } GstBufferFlag;
A set of buffer flags used to describe properties of a GstBuffer.
GST_BUFFER_FLAG_READONLY
|
the buffer is read-only. This means the data of the buffer should not be modified. The metadata might still be modified. |
GST_BUFFER_FLAG_PREROLL
|
the buffer is part of a preroll and should not be displayed. |
GST_BUFFER_FLAG_DISCONT
|
the buffer marks a discontinuity in the stream. This typically occurs after a seek or a dropped buffer from a live or network source. |
GST_BUFFER_FLAG_IN_CAPS
|
the buffer has been added as a field in a GstCaps. |
GST_BUFFER_FLAG_GAP
|
the buffer has been created to fill a gap in the stream and contains media neutral data (elements can switch to optimized code path that ignores the buffer content). |
GST_BUFFER_FLAG_DELTA_UNIT
|
this unit cannot be decoded independently. |
GST_BUFFER_FLAG_MEDIA1
|
a flag whose use is specific to the caps of the buffer. Since: 0.10.23 |
GST_BUFFER_FLAG_MEDIA2
|
a flag whose use is specific to the caps of the buffer. Since: 0.10.23 |
GST_BUFFER_FLAG_MEDIA3
|
a flag whose use is specific to the caps of the buffer. Since: 0.10.23 |
GST_BUFFER_FLAG_LAST
|
additional flags can be added starting from this flag. |
typedef enum { GST_BUFFER_COPY_FLAGS = (1 << 0), GST_BUFFER_COPY_TIMESTAMPS = (1 << 1), GST_BUFFER_COPY_CAPS = (1 << 2) } GstBufferCopyFlags;
A set of flags that can be provided to the gst_buffer_copy_metadata()
function to specify which metadata fields should be copied.
Since 0.10.13
#define GST_BUFFER_FLAGS(buf) GST_MINI_OBJECT_FLAGS(buf)
A flags word containing GstBufferFlag flags set on this buffer.
buf : |
a GstBuffer. |
#define GST_BUFFER_FLAG_IS_SET(buf,flag) GST_MINI_OBJECT_FLAG_IS_SET (buf, flag)
Gives the status of a specific flag on a buffer.
buf : |
a GstBuffer. |
flag : |
the GstBufferFlag to check. |
#define GST_BUFFER_FLAG_SET(buf,flag) GST_MINI_OBJECT_FLAG_SET (buf, flag)
Sets a buffer flag on a buffer.
buf : |
a GstBuffer. |
flag : |
the GstBufferFlag to set. |
#define GST_BUFFER_FLAG_UNSET(buf,flag) GST_MINI_OBJECT_FLAG_UNSET (buf, flag)
Clears a buffer flag.
buf : |
a GstBuffer. |
flag : |
the GstBufferFlag to clear. |
#define GST_BUFFER_DATA(buf) (GST_BUFFER_CAST(buf)->data)
A pointer to the data element of this buffer.
buf : |
a GstBuffer. |
#define GST_BUFFER_MALLOCDATA(buf) (GST_BUFFER_CAST(buf)->malloc_data)
A pointer to any data allocated for this buffer using g_malloc()
. If this is
non-NULL, this memory will be freed at the end of the buffer's lifecycle
(i.e. when its refcount becomes zero).
buf : |
a GstBuffer. |
#define GST_BUFFER_FREE_FUNC(buf) (GST_BUFFER_CAST(buf)->free_func)
A pointer to a function that will be called on the buffer's malloc_data when
this buffer is finalized. Defaults to g_free()
.
Note that the free function only affects the buffer's malloc_data; if the
buffer's malloc_data is NULL
, the function will not be called.
buf : |
a GstBuffer. |
Since 0.10.22
#define GST_BUFFER_SIZE(buf) (GST_BUFFER_CAST(buf)->size)
The size in bytes of the data in this buffer.
buf : |
a GstBuffer. |
#define GST_BUFFER_TIMESTAMP(buf) (GST_BUFFER_CAST(buf)->timestamp)
The timestamp in nanoseconds (as a GstClockTime) of the data in the buffer.
Value will be GST_CLOCK_TIME_NONE
if the timestamp is unknown.
buf : |
a GstBuffer.: |
#define GST_BUFFER_DURATION(buf) (GST_BUFFER_CAST(buf)->duration)
The duration in nanoseconds (as a GstClockTime) of the data in the buffer.
Value will be GST_CLOCK_TIME_NONE
if the duration is unknown.
buf : |
a GstBuffer. |
#define GST_BUFFER_CAPS(buf) (GST_BUFFER_CAST(buf)->caps)
The caps for this buffer.
buf : |
a GstBuffer. |
#define GST_BUFFER_OFFSET(buf) (GST_BUFFER_CAST(buf)->offset)
The offset in the source file of the beginning of this buffer.
buf : |
a GstBuffer. |
#define GST_BUFFER_OFFSET_END(buf) (GST_BUFFER_CAST(buf)->offset_end)
The offset in the source file of the end of this buffer.
buf : |
a GstBuffer. |
#define GST_BUFFER_OFFSET_NONE ((guint64)-1)
Constant for no-offset return results.
#define GST_BUFFER_DURATION_IS_VALID(buffer) (GST_CLOCK_TIME_IS_VALID (GST_BUFFER_DURATION (buffer)))
Tests if the duration is known.
buffer : |
a GstBuffer |
#define GST_BUFFER_TIMESTAMP_IS_VALID(buffer) (GST_CLOCK_TIME_IS_VALID (GST_BUFFER_TIMESTAMP (buffer)))
Tests if the timestamp is known.
buffer : |
a GstBuffer |
#define GST_BUFFER_OFFSET_IS_VALID(buffer) (GST_BUFFER_OFFSET (buffer) != GST_BUFFER_OFFSET_NONE)
Tests if the start offset is known.
buffer : |
a GstBuffer |
#define GST_BUFFER_OFFSET_END_IS_VALID(buffer) (GST_BUFFER_OFFSET_END (buffer) != GST_BUFFER_OFFSET_NONE)
Tests if the end offset is known.
buffer : |
a GstBuffer |
#define GST_BUFFER_IS_DISCONT(buffer) (GST_BUFFER_FLAG_IS_SET (buffer, GST_BUFFER_FLAG_DISCONT))
Tests if the buffer marks a discontinuity in the stream.
buffer : |
a GstBuffer |
Since 0.10.9
#define GST_BUFFER_TRACE_NAME "GstBuffer"
The name used for tracing memory allocations.
GstBuffer* gst_buffer_new (void);
Creates a newly allocated buffer without any data.
MT safe.
Returns : | the new GstBuffer. |
GstBuffer* gst_buffer_new_and_alloc (guint size);
Creates a newly allocated buffer with data of the given size.
The buffer memory is not cleared. If the requested amount of
memory can't be allocated, the program will abort. Use
gst_buffer_try_new_and_alloc()
if you want to handle this case
gracefully or have gotten the size to allocate from an untrusted
source such as a media stream.
Note that when size
== 0, the buffer data pointer will be NULL.
MT safe.
size : |
the size of the new buffer's data. |
Returns : | the new GstBuffer. |
GstBuffer* gst_buffer_try_new_and_alloc (guint size);
Tries to create a newly allocated buffer with data of the given size. If the requested amount of memory can't be allocated, NULL will be returned. The buffer memory is not cleared.
Note that when size
== 0, the buffer data pointer will be NULL.
MT safe.
size : |
the size of the new buffer's data. |
Returns : | a new GstBuffer, or NULL if the memory couldn't be allocated. |
Since 0.10.13
GstBuffer* gst_buffer_ref (GstBuffer *buf);
Increases the refcount of the given buffer by one.
Note that the refcount affects the writeability
of buf
and its metadata, see gst_buffer_is_writable()
and
gst_buffer_is_metadata_writable()
. It is
important to note that keeping additional references to
GstBuffer instances can potentially increase the number
of memcpy operations in a pipeline.
buf : |
a GstBuffer. |
Returns : | buf
|
void gst_buffer_unref (GstBuffer *buf);
Decreases the refcount of the buffer. If the refcount reaches 0, the buffer
will be freed. If GST_BUFFER_MALLOCDATA()
is non-NULL, this pointer will
also be freed at this time.
buf : |
a GstBuffer. |
#define gst_buffer_set_data(buf, data, size)
A convenience function to set the data and size on a buffer.
This will replace any existing data pointer set on this buffer, but will
not change GST_BUFFER_MALLOCDATA()
, if any. Callers should ensure that
GST_BUFFER_MALLOCDATA()
is non-NULL, or should free that and set it to NULL.
No checks are done on the data or size arguments passed.
buf : |
a GstBuffer |
data : |
The data (a guint8 *) to set on the buffer. |
size : |
The size (in bytes, as a guint) of the data being set. |
GstBuffer* gst_buffer_copy (const GstBuffer *buf);
Create a copy of the given buffer. This will also make a newly allocated copy of the data the source buffer contains.
buf : |
a GstBuffer. |
Returns : | a new copy of buf .
|
#define GST_BUFFER_COPY_ALL (GST_BUFFER_COPY_FLAGS | GST_BUFFER_COPY_TIMESTAMPS | GST_BUFFER_COPY_CAPS)
Combination of all possible fields that can be copied with
gst_buffer_copy_metadata()
.
Since 0.10.13
void gst_buffer_copy_metadata (GstBuffer *dest, const GstBuffer *src, GstBufferCopyFlags flags);
Copies the metadata from src
into dest
. The data, size and mallocdata
fields are not copied.
flags
indicate which fields will be copied. Use GST_BUFFER_COPY_ALL to copy
all the metadata fields.
This function is typically called from a custom buffer copy function after
creating dest
and setting the data, size, mallocdata.
dest : |
a destination GstBuffer |
src : |
a source GstBuffer |
flags : |
flags indicating what metadata fields should be copied. |
Since 0.10.13
#define gst_buffer_is_writable(buf) gst_mini_object_is_writable (GST_MINI_OBJECT_CAST (buf))
Tests if you can safely write data into a buffer's data array or validly modify the caps and timestamp metadata. Metadata in a GstBuffer is always writable, but it is only safe to change it when there is only one owner of the buffer - ie, the refcount is 1.
buf : |
a GstBuffer |
#define gst_buffer_make_writable(buf) GST_BUFFER_CAST (gst_mini_object_make_writable (GST_MINI_OBJECT_CAST (buf)))
Makes a writable buffer from the given buffer. If the source buffer is
already writable, this will simply return the same buffer. A copy will
otherwise be made using gst_buffer_copy()
.
buf : |
a GstBuffer |
gboolean gst_buffer_is_metadata_writable (GstBuffer *buf);
Similar to gst_buffer_is_writable, but this only ensures that the refcount of the buffer is 1, indicating that the caller is the sole owner and can change the buffer metadata, such as caps and timestamps.
buf : |
a GstBuffer |
Returns : | TRUE if the metadata is writable. |
GstBuffer* gst_buffer_make_metadata_writable (GstBuffer *buf);
Similar to gst_buffer_make_writable, but does not ensure that the buffer data array is writable. Instead, this just ensures that the returned buffer is solely owned by the caller, by creating a subbuffer of the original buffer if necessary.
After calling this function, buf
should not be referenced anymore. The
result of this function has guaranteed writable metadata.
#define gst_buffer_replace(obuf,nbuf)
Modifies a pointer to a Gstbuffer to point to a different GstBuffer. The modification is done atomically (so this is useful for ensuring thread safety in some cases), and the reference counts are updated appropriately (the old buffer is unreffed, the new is reffed).
Either nbuf
or the GstBuffer pointed to by obuf
may be NULL.
GstCaps* gst_buffer_get_caps (GstBuffer *buffer);
Gets the media type of the buffer. This can be NULL if there is no media type attached to this buffer.
void gst_buffer_set_caps (GstBuffer *buffer, GstCaps *caps);
Sets the media type on the buffer. The refcount of the caps will be increased and any previous caps on the buffer will be unreffed.
GstBuffer* gst_buffer_create_sub (GstBuffer *parent, guint offset, guint size);
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.
gboolean gst_buffer_is_span_fast (GstBuffer *buf1, GstBuffer *buf2);
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.
GstBuffer* gst_buffer_span (GstBuffer *buf1, guint32 offset, GstBuffer *buf2, guint32 len);
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.
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. |
len : |
the total length of the new buffer. |
Returns : | the new GstBuffer that spans the two source buffers. Returns NULL if the arguments are invalid. |
void gst_buffer_stamp (GstBuffer *dest, const GstBuffer *src);
gst_buffer_stamp
is deprecated and should not be used in newly-written code. use gst_buffer_copy_metadata()
instead, it provides more
control.
Copies additional information (the timestamp, duration, and offset start and end) from one buffer to the other.
This function does not copy any buffer flags or caps and is equivalent to
gst_buffer_copy_metadata(dest
, src
, GST_BUFFER_COPY_TIMESTAMPS).
dest : |
buffer to stamp |
src : |
buffer to stamp from |
GstBuffer* gst_buffer_join (GstBuffer *buf1, GstBuffer *buf2);
Create a new buffer that is the concatenation of the two source buffers, and unrefs the original source buffers.
If the buffers point to contiguous areas of memory, the buffer is created without copying the data.
This is a convenience function for C programmers. See also
gst_buffer_merge()
, which does the same thing without
unreffing the input parameters. Language bindings without
explicit reference counting should not wrap this function.
GstBuffer* gst_buffer_merge (GstBuffer *buf1, GstBuffer *buf2);
Create a new buffer that is the concatenation of the two source buffers. The original source buffers will not be modified or unref'd. Make sure you unref the source buffers if they are not used anymore afterwards.
If the buffers point to contiguous areas of memory, the buffer is created without copying the data.