GstBuffer

## GstBuffer GstBuffer — Data-passing buffer type, supporting sub-buffers. |

## Synopsis

    #include <gst/gst.h>

                GstBuffer;
    GstBuffer*  gst_buffer_new                  (void);
    GstBuffer*  gst_buffer_new_and_alloc        (guint size);
    enum        GstBufferFlag;
    #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_set_data             (buf, data, size)
    #define     GST_BUFFER_DATA                 (buf)
    #define     GST_BUFFER_SIZE                 (buf)
    #define     GST_BUFFER_MAXSIZE              (buf)
    #define     GST_BUFFER_TIMESTAMP            (buf)
    #define     GST_BUFFER_DURATION             (buf)
    #define     GST_BUFFER_OFFSET               (buf)
    #define     GST_BUFFER_OFFSET_END           (buf)
    #define     gst_buffer_ref                  (buf)
    #define     gst_buffer_ref_by_count         (buf,c)
    #define     gst_buffer_unref                (buf)
    void        gst_buffer_stamp                (GstBuffer *dest,
                                                 const GstBuffer *src);
    #define     gst_buffer_copy                 (buf)
    #define     gst_buffer_is_writable          (buf)
    #define     gst_buffer_copy_on_write        (buf)
    GstBuffer*  gst_buffer_create_sub           (GstBuffer *parent,
                                                 guint offset,
                                                 guint size);
    GstBuffer*  gst_buffer_join                 (GstBuffer *buf1,
                                                 GstBuffer *buf2);
    GstBuffer*  gst_buffer_merge                (GstBuffer *buf1,
                                                 GstBuffer *buf2);
    GstBuffer*  gst_buffer_span                 (GstBuffer *buf1,
                                                 guint32 offset,
                                                 GstBuffer *buf2,
                                                 guint32 len);
    gboolean    gst_buffer_is_span_fast         (GstBuffer *buf1,
                                                 GstBuffer *buf2);
    void        gst_buffer_default_free         (GstBuffer *buffer);
    GstBuffer*  gst_buffer_default_copy         (GstBuffer *buffer);
    #define     GST_BUFFER_TRACE_NAME
    #define     GST_BUFFER_REFCOUNT             (buf)
    #define     GST_BUFFER_REFCOUNT_VALUE       (buf)
    #define     GST_BUFFER_COPY_FUNC            (buf)
    #define     GST_BUFFER_FREE_FUNC            (buf)
    #define     GST_BUFFER_FREE_DATA_FUNC       (buf)
    void        (*GstBufferFreeDataFunc)        (GstBuffer *buffer);
    #define     GST_BUFFER_PRIVATE              (buf)
    #define     GST_BUFFER_OFFSET_NONE
    #define     GST_BUFFER_MAXSIZE_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_MAXSIZE_IS_VALID     (buffer)

## Description

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.

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_DATA (buffer) = g_alloc (size);
      ...

Alternatively, use `gst_buffer_new_and_alloc()` to create a buffer with preallocated data of a given size.

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.

`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 the plug-in wants to modify the buffer in-place, it should first obtain a buffer that is safe to modify by using `gst_buffer_copy_on_write()`. 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 it 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 usually are freed by unreffing them with `gst_buffer_unref()`. Do not use `gst_buffer_free()` : this function effectively frees the buffer regardless of the refcount, which is dangerous.

Last reviewed on August 12th, 2004 (0.8.5)

## Details

### GstBuffer

    typedef struct {
      GstData		 data_type;

      /* pointer to data and its size */
      guint8		*data;			/* pointer to buffer data */
      guint			 size;			/* size of buffer data */
      guint			 maxsize;		/* max size of this buffer */

      /* timestamp */
      GstClockTime		 timestamp;
      GstClockTime		 duration;

      /* media specific offset
       * for video frames, this could be the number of frames,
       * for audio data, this could be the number of audio samples,
       * for file data or compressed data, this could be the number of bytes
       * offset_end is the last offset contained in the buffer. The format specifies
       * the meaning of both of them exactly.
       */
      guint64		 offset;
      guint64		 offset_end;

      GstBufferFreeDataFunc  free_data;
      gpointer		 buffer_private;

      gpointer _gst_reserved[GST_PADDING];
    } GstBuffer;

The basic structure of a buffer.

### gst_buffer_new ()

    GstBuffer*  gst_buffer_new                  (void);

Creates a newly allocated buffer without any data.

Returns : | the new GstBuffer.

### gst_buffer_new_and_alloc ()

    GstBuffer*  gst_buffer_new_and_alloc        (guint size);

Creates a newly allocated buffer with data of the given size.

`size` : | the size of the new buffer's data.
Returns : | the new GstBuffer.

### enum GstBufferFlag

    typedef enum {
      GST_BUFFER_READONLY   = GST_DATA_READONLY,
      GST_BUFFER_SUBBUFFER  = GST_DATA_FLAG_LAST,
      GST_BUFFER_ORIGINAL,
      GST_BUFFER_DONTFREE,
      GST_BUFFER_KEY_UNIT,		/* deprecated, use reverse DELTA_UNIT */
      GST_BUFFER_DONTKEEP,    /* FIXME: is this deprecated ? there is no reference in gstreamer, gst-plugins */
      GST_BUFFER_IN_CAPS,
      GST_BUFFER_DELTA_UNIT,	/* this unit depends on a previous unit */
      GST_BUFFER_FLAG_LAST	= GST_DATA_FLAG_LAST + 8
    } GstBufferFlag;

A set of buffer flags used to describe properties of a GstBuffer.

`GST_BUFFER_READONLY` | the buffer is read-only.
`GST_BUFFER_SUBBUFFER` | the buffer is a subbuffer, the parent buffer can be found with the `GST_BUFFER_POOL_PRIVATE()` macro.
`GST_BUFFER_ORIGINAL` | buffer is not a copy of another buffer.
`GST_BUFFER_DONTFREE` | do not try to free the data when this buffer is unreferenced.
`GST_BUFFER_KEY_UNIT` | the buffer holds a key unit, a unit that can be decoded independently of other buffers. This flag has been deprecated, see GST_BUFFER_DELTA_UNIT.
`GST_BUFFER_DONTKEEP` | the buffer should not be `ref()`ed, but copied instead before doing anything with it (for specially allocated hw buffers and such)
`GST_BUFFER_IN_CAPS` | the buffer has been added as a field in a GstCaps.
`GST_BUFFER_DELTA_UNIT` | this unit cannot be decoded independently. Since 0.8.5
`GST_BUFFER_FLAG_LAST` | additional flags can be added starting from this flag.

### GST_BUFFER_FLAGS()

    #define GST_BUFFER_FLAGS(buf)                   GST_DATA_FLAGS(buf)

Gets the flags from this buffer.

`buf` : | a GstBuffer to retrieve the flags from.

### GST_BUFFER_FLAG_IS_SET()

    #define GST_BUFFER_FLAG_IS_SET(buf,flag)        GST_DATA_FLAG_IS_SET (buf, flag)

Gives the status of a given flag of a buffer.

`buf` : | a GstBuffer to query flags of.
`flag` : | the GstBufferFlag to check.

### GST_BUFFER_FLAG_SET()

    #define GST_BUFFER_FLAG_SET(buf,flag)           GST_DATA_FLAG_SET (buf, flag)

Sets a buffer flag.

`buf` : | a GstBuffer to modify flags of.
`flag` : | the GstBufferFlag to set.

### GST_BUFFER_FLAG_UNSET()

    #define GST_BUFFER_FLAG_UNSET(buf,flag)         GST_DATA_FLAG_UNSET (buf, flag)

Clears a buffer flag.

`buf` : | a GstBuffer to modify flags of.
`flag` : | the GstBufferFlag to clear.

### gst_buffer_set_data()

    #define     gst_buffer_set_data(buf, data, size)

### Warning

`gst_buffer_set_data` is deprecated and should not be used in newly-written code.

A convenience function to set the data and size on a buffer

`buf` : | The buffer to modify
`data` : | The data to set on the buffer
`size` : | The size to set on the buffer

### GST_BUFFER_DATA()

    #define GST_BUFFER_DATA(buf)			(GST_BUFFER(buf)->data)

Retrieves a pointer to the data element of this buffer.

`buf` : | a GstBuffer to get data pointer of.
Returns : | the pointer to the actual data contents of the buffer.

### GST_BUFFER_SIZE()

    #define GST_BUFFER_SIZE(buf)			(GST_BUFFER(buf)->size)

Gets the size of the data in this buffer.

`buf` : | a GstBuffer to get data size of.

### GST_BUFFER_MAXSIZE()

    #define GST_BUFFER_MAXSIZE(buf)			(GST_BUFFER(buf)->maxsize)

Gets the maximum size of this buffer.

`buf` : | a GstBuffer to get maximum size of.

### GST_BUFFER_TIMESTAMP()

    #define GST_BUFFER_TIMESTAMP(buf)		(GST_BUFFER(buf)->timestamp)

Gets the timestamp for this buffer.

`buf` : | a GstBuffer to get timestamp of.

### GST_BUFFER_DURATION()

    #define GST_BUFFER_DURATION(buf)		(GST_BUFFER(buf)->duration)

Gets the duration in nanoseconds of the data in the buffer. Value will be GST_CLOCK_TIME_NONE if the duration is unknown.

`buf` : | a GstBuffer to get the duration from.

### GST_BUFFER_OFFSET()

    #define GST_BUFFER_OFFSET(buf)			(GST_BUFFER(buf)->offset)

Gets the offset in the source file of the beinning of this buffer.

`buf` : | a GstBuffer to get offset of.

### GST_BUFFER_OFFSET_END()

    #define GST_BUFFER_OFFSET_END(buf)		(GST_BUFFER(buf)->offset_end)

Gets the offset in the source file of the end of this buffer.

`buf` : | a GstBuffer to get offset of.

### gst_buffer_ref()

    #define		gst_buffer_ref(buf)		GST_BUFFER (gst_data_ref (GST_DATA (buf)))

Increases the refcount of the given buffer by one.

`buf` : | a GstBuffer to increase the refcount of.

### gst_buffer_ref_by_count()

    #define		gst_buffer_ref_by_count(buf,c)	GST_BUFFER (gst_data_ref_by_count (GST_DATA (buf), c))

Increases the refcount of the buffer by the given value.

`buf` : | a GstBuffer to increase the refcount of.
`c` : | the value to add to the refcount.

### gst_buffer_unref()

    #define		gst_buffer_unref(buf)		gst_data_unref (GST_DATA (buf))

Decreases the refcount of the buffer. If the refcount reaches 0, the buffer will be freed.

`buf` : | a GstBuffer to unref.

### gst_buffer_stamp ()

    void        gst_buffer_stamp                (GstBuffer *dest,
                                                 const GstBuffer *src);

Copies additional information (timestamps and offsets) from one buffer to the other.

`dest` : | buffer to stamp
`src` : | buffer to stamp from

### gst_buffer_copy()

    #define		gst_buffer_copy(buf)		GST_BUFFER (gst_data_copy (GST_DATA (buf)))

Copies the given buffer using the copy function of the parent GstData structure.

`buf` : | a GstBuffer to copy.
Returns : | a new GstBuffer copy of the buffer.

### gst_buffer_is_writable()

    #define		gst_buffer_is_writable(buf)	gst_data_is_writable (GST_DATA (buf))

Tests if you can safely write data into a buffer's data array.

`buf` : | a GstBuffer to check

### gst_buffer_copy_on_write()

    #define		gst_buffer_copy_on_write(buf)   GST_BUFFER (gst_data_copy_on_write (GST_DATA (buf)))

This function returns a buffer that is safe to write to. Copy the buffer if the refcount > 1 so that the newly created buffer can be safely written to. If the refcount is 1, this function just returns the original buffer.

`buf` : | a GstBuffer to copy
Returns : | the GstBuffer that can safely be written to.

### gst_buffer_create_sub ()

    GstBuffer*  gst_buffer_create_sub           (GstBuffer *parent,
                                                 guint offset,
                                                 guint size);

Creates a sub-buffer from the parent at a given offset. This sub-buffer uses the actual memory space of the parent buffer. This function will copy the offset and timestamp field when the offset is 0, else they are set to _NONE. The duration field of the new buffer are set to GST_CLOCK_TIME_NONE.

`parent` : | a parent GstBuffer to create a subbuffer from.
`offset` : | the offset into parent GstBuffer.
`size` : | the size of the new GstBuffer sub-buffer (with size > 0).
Returns : | the new GstBuffer, or NULL if there was an error.

### gst_buffer_join ()

    GstBuffer*  gst_buffer_join                 (GstBuffer *buf1,
                                                 GstBuffer *buf2);

Create a new buffer that is the concatenation of the two source buffers. The original buffers are unreferenced.

If the buffers point to contiguous areas of memory, the buffer is created without copying the data.

`buf1` : | a first source GstBuffer to merge.
`buf2` : | the second source GstBuffer to merge.
Returns : | the new GstBuffer that's the concatenation of the source buffers.

### gst_buffer_merge ()

    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.

WARNING: Incorrect use of this function can lead to memory leaks. It is recommended to use `gst_buffer_join()` instead of this function.

If the buffers point to contiguous areas of memory, the buffer is created without copying the data.

`buf1` : | a first source GstBuffer to merge.
`buf2` : | the second source GstBuffer to merge.
Returns : | the new GstBuffer that's the concatenation of the source buffers.

### gst_buffer_span ()

    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.

`buf1` : | a 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.

### gst_buffer_is_span_fast ()

    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.

`buf1` : | a first source GstBuffer.
`buf2` : | the second source GstBuffer.
Returns : | TRUE if the buffers are contiguous, FALSE if a copy would be required.

### gst_buffer_default_free ()

    void        gst_buffer_default_free         (GstBuffer *buffer);

Frees the memory associated with the buffer including the buffer data, unless the GST_BUFFER_DONTFREE flags was set or the buffer data is NULL.

`buffer` : | a GstBuffer to free.

### gst_buffer_default_copy ()

    GstBuffer*  gst_buffer_default_copy         (GstBuffer *buffer);

Make a full newly allocated copy of the given buffer, data and all.

`buffer` : | a GstBuffer to make a copy of.
Returns : | the new GstBuffer.

### GST_BUFFER_TRACE_NAME

    #define GST_BUFFER_TRACE_NAME		"GstBuffer"

The name used for tracing memory allocations

### GST_BUFFER_REFCOUNT()

    #define GST_BUFFER_REFCOUNT(buf)		GST_DATA_REFCOUNT(buf)

Gets a handle to the refcount structure of the buffer.

`buf` : | a GstBuffer to get the refcount structure of.

### GST_BUFFER_REFCOUNT_VALUE()

    #define GST_BUFFER_REFCOUNT_VALUE(buf)		GST_DATA_REFCOUNT_VALUE(buf)

Gets the current refcount value of the buffer.

`buf` : | a GstBuffer to get the refcount value of.

### GST_BUFFER_COPY_FUNC()

    #define GST_BUFFER_COPY_FUNC(buf)		GST_DATA_COPY_FUNC(buf)

### Warning

`GST_BUFFER_COPY_FUNC` is deprecated and should not be used in newly-written code.

Calls the buffer-specific copy function on the given buffer.

`buf` : | a GstBuffer to copy.

### GST_BUFFER_FREE_FUNC()

    #define GST_BUFFER_FREE_FUNC(buf)		GST_DATA_FREE_FUNC(buf)

### Warning

`GST_BUFFER_FREE_FUNC` is deprecated and should not be used in newly-written code.

Calls the buffer-specific free function on the given buffer.

`buf` : | a GstBuffer to free.

### GST_BUFFER_FREE_DATA_FUNC()

    #define GST_BUFFER_FREE_DATA_FUNC(buf)          (GST_BUFFER(buf)->free_data)

A function that should be called if the buffer has no more references left. Elements that utilize hardware memory could use this to re-queue the buffer after it's been unreferenced. If no free_data_func has been provided, the default will be used which simply deallocates the memory region and the GstBuffer object. Manual implementations that want to free their own memory but don't do anything special otherwise are suggested to set the GST_BUFFER_DONTFREE flag on the buffer and call the default data free function (`gst_buffer_default_free()`) from their manual implementation.

`buf` : | the GstBuffer this function belongs to

### GstBufferFreeDataFunc ()

    void        (*GstBufferFreeDataFunc)        (GstBuffer *buffer);

the type for the GST_BUFFER_FREE_DATA_FUNC

`buffer` : | the GstBuffer on which it will operate, when called

### GST_BUFFER_PRIVATE()

    #define GST_BUFFER_PRIVATE(buf)                 (GST_BUFFER(buf)->buffer_private)

Private data for the buffer. This can be used to store a pointer to the object that can then be retrieved in something like the BUFFER_FREE_DATA_FUNC.

`buf` : | the GstBuffer this data belongs to

### GST_BUFFER_OFFSET_NONE

    #define GST_BUFFER_OFFSET_NONE	((guint64)-1)

### GST_BUFFER_MAXSIZE_NONE

    #define GST_BUFFER_MAXSIZE_NONE	((guint)0)

### GST_BUFFER_DURATION_IS_VALID()

    #define GST_BUFFER_DURATION_IS_VALID(buffer)	(GST_CLOCK_TIME_IS_VALID (GST_BUFFER_DURATION (buffer)))

Tests if the duration is known.

`buffer` : | the GstBuffer to check for the duration

### GST_BUFFER_TIMESTAMP_IS_VALID()

    #define GST_BUFFER_TIMESTAMP_IS_VALID(buffer)	(GST_CLOCK_TIME_IS_VALID (GST_BUFFER_TIMESTAMP (buffer)))

Tests if the timestamp is known.

`buffer` : | the GstBuffer to check for the timestamp

### GST_BUFFER_OFFSET_IS_VALID()

    #define GST_BUFFER_OFFSET_IS_VALID(buffer)	(GST_BUFFER_OFFSET (buffer) != GST_BUFFER_OFFSET_NONE)

`buffer` : |

### GST_BUFFER_OFFSET_END_IS_VALID()

    #define GST_BUFFER_OFFSET_END_IS_VALID(buffer)	(GST_BUFFER_OFFSET_END (buffer) != GST_BUFFER_OFFSET_NONE)

`buffer` : |

### GST_BUFFER_MAXSIZE_IS_VALID()

    #define GST_BUFFER_MAXSIZE_IS_VALID(buffer)	(GST_BUFFER_MAXSIZE (buffer) != GST_BUFFER_MAXSIZE_NONE)

`buffer` : |

## See Also

GstBufferPool, GstPad, GstData