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AVBuffer
Data Structures

AVBuffer is an API for reference-counted data buffers. More...

Files

file  buffer.h
 refcounted data buffer API
 

Data Structures

struct  AVBufferRef
 A reference to a data buffer. More...
 

Macros

#define AV_BUFFER_FLAG_READONLY   (1 << 0)
 Always treat the buffer as read-only, even when it has only one reference.
 

Functions

AVBufferRefav_buffer_alloc (int size)
 Allocate an AVBuffer of the given size using av_malloc().
 
AVBufferRefav_buffer_allocz (int size)
 Same as av_buffer_alloc(), except the returned buffer will be initialized to zero.
 
AVBufferRefav_buffer_create (uint8_t *data, int size, void(*free)(void *opaque, uint8_t *data), void *opaque, int flags)
 Create an AVBuffer from an existing array.
 
void av_buffer_default_free (void *opaque, uint8_t *data)
 Default free callback, which calls av_free() on the buffer data.
 
AVBufferRefav_buffer_ref (AVBufferRef *buf)
 Create a new reference to an AVBuffer.
 
void av_buffer_unref (AVBufferRef **buf)
 Free a given reference and automatically free the buffer if there are no more references to it.
 
int av_buffer_is_writable (const AVBufferRef *buf)
 
voidav_buffer_get_opaque (const AVBufferRef *buf)
 
int av_buffer_get_ref_count (const AVBufferRef *buf)
 
int av_buffer_make_writable (AVBufferRef **buf)
 Create a writable reference from a given buffer reference, avoiding data copy if possible.
 
int av_buffer_realloc (AVBufferRef **buf, int size)
 Reallocate a given buffer.
 

Detailed Description

AVBuffer is an API for reference-counted data buffers.

There are two core objects in this API – AVBuffer and AVBufferRef. AVBuffer represents the data buffer itself; it is opaque and not meant to be accessed by the caller directly, but only through AVBufferRef. However, the caller may e.g. compare two AVBuffer pointers to check whether two different references are describing the same data buffer. AVBufferRef represents a single reference to an AVBuffer and it is the object that may be manipulated by the caller directly.

There are two functions provided for creating a new AVBuffer with a single reference – av_buffer_alloc() to just allocate a new buffer, and av_buffer_create() to wrap an existing array in an AVBuffer. From an existing reference, additional references may be created with av_buffer_ref(). Use av_buffer_unref() to free a reference (this will automatically free the data once all the references are freed).

The convention throughout this API and the rest of FFmpeg is such that the buffer is considered writable if there exists only one reference to it (and it has not been marked as read-only). The av_buffer_is_writable() function is provided to check whether this is true and av_buffer_make_writable() will automatically create a new writable buffer when necessary. Of course nothing prevents the calling code from violating this convention, however that is safe only when all the existing references are under its control.

Note
Referencing and unreferencing the buffers is thread-safe and thus may be done from multiple threads simultaneously without any need for additional locking.
Two different references to the same buffer can point to different parts of the buffer (i.e. their AVBufferRef.data will not be equal).

Macro Definition Documentation

#define AV_BUFFER_FLAG_READONLY   (1 << 0)

Always treat the buffer as read-only, even when it has only one reference.

Definition at line 113 of file buffer.h.

Referenced by av_buffer_create(), av_buffer_is_writable(), dxva2_get_buffer(), vda_h264_end_frame(), and vdpau_get_buffer().

Function Documentation

AVBufferRef* av_buffer_alloc ( int  size)
AVBufferRef* av_buffer_allocz ( int  size)
AVBufferRef* av_buffer_create ( uint8_t data,
int  size,
void(*)(void *opaque, uint8_t *data free,
void opaque,
int  flags 
)

Create an AVBuffer from an existing array.

If this function is successful, data is owned by the AVBuffer. The caller may only access data through the returned AVBufferRef and references derived from it. If this function fails, data is left untouched.

Parameters
datadata array
sizesize of data in bytes
freea callback for freeing this buffer's data
opaqueparameter to be got for processing or passed to free
flagsa combination of AV_BUFFER_FLAG_*
Returns
an AVBufferRef referring to data on success, NULL on failure.

Definition at line 28 of file buffer.c.

Referenced by av_buffer_alloc(), av_buffer_pool_get(), av_buffer_realloc(), av_packet_from_data(), dxva2_get_buffer(), ff_hevc_decode_nal_pps(), filter_packet(), get_buffer2(), get_buffer_internal(), mmap_read_frame(), vda_h264_end_frame(), vda_old_h264_end_frame(), vdpau_get_buffer(), and write_frame().

void av_buffer_default_free ( void opaque,
uint8_t data 
)

Default free callback, which calls av_free() on the buffer data.

This function is meant to be passed to av_buffer_create(), not called directly.

Definition at line 61 of file buffer.c.

Referenced by av_buffer_alloc(), av_buffer_create(), av_buffer_realloc(), av_packet_from_data(), filter_packet(), and write_frame().

AVBufferRef* av_buffer_ref ( AVBufferRef buf)
void av_buffer_unref ( AVBufferRef **  buf)
int av_buffer_is_writable ( const AVBufferRef buf)
Returns
1 if the caller may write to the data referred to by buf (which is true if and only if buf is the only reference to the underlying AVBuffer). Return 0 otherwise. A positive answer is valid until av_buffer_ref() is called on buf.

Definition at line 132 of file buffer.c.

Referenced by av_buffer_make_writable(), av_buffer_realloc(), and av_frame_is_writable().

void* av_buffer_get_opaque ( const AVBufferRef buf)
Returns
the opaque parameter set by av_buffer_create.

Definition at line 140 of file buffer.c.

Referenced by vdadec_decode().

int av_buffer_get_ref_count ( const AVBufferRef buf)

Definition at line 145 of file buffer.c.

Referenced by ff_h264_decode_ref_pic_list_reordering().

int av_buffer_make_writable ( AVBufferRef **  buf)

Create a writable reference from a given buffer reference, avoiding data copy if possible.

Parameters
bufbuffer reference to make writable. On success, buf is either left untouched, or it is unreferenced and a new writable AVBufferRef is written in its place. On failure, buf is left untouched.
Returns
0 on success, a negative AVERROR on failure.

Definition at line 150 of file buffer.c.

int av_buffer_realloc ( AVBufferRef **  buf,
int  size 
)

Reallocate a given buffer.

Parameters
bufa buffer reference to reallocate. On success, buf will be unreferenced and a new reference with the required size will be written in its place. On failure buf will be left untouched. *buf may be NULL, then a new buffer is allocated.
sizerequired new buffer size.
Returns
0 on success, a negative AVERROR on failure.
Note
the buffer is actually reallocated with av_realloc() only if it was initially allocated through av_buffer_realloc(NULL) and there is only one reference to it (i.e. the one passed to this function). In all other cases a new buffer is allocated and the data is copied.

Definition at line 168 of file buffer.c.

Referenced by av_buffer_realloc(), av_grow_packet(), avcodec_encode_audio2(), avcodec_encode_video2(), decode(), and packet_alloc().