GstBufferPool: GStreamer 1.0 Core Reference Manual

## GstBufferPool GstBufferPool — Pool for buffers |

## Functions

#define | GST_BUFFER_POOL_IS_FLUSHING()
GstBufferPool * | gst_buffer_pool_new ()
gboolean | gst_buffer_pool_config_get_params ()
void | gst_buffer_pool_config_set_params ()
gboolean | gst_buffer_pool_config_validate_params ()
gboolean | gst_buffer_pool_config_get_allocator ()
void | gst_buffer_pool_config_set_allocator ()
guint | gst_buffer_pool_config_n_options ()
void | gst_buffer_pool_config_add_option ()
const gchar * | gst_buffer_pool_config_get_option ()
gboolean | gst_buffer_pool_config_has_option ()
const gchar ** | gst_buffer_pool_get_options ()
gboolean | gst_buffer_pool_has_option ()
GstStructure * | gst_buffer_pool_get_config ()
gboolean | gst_buffer_pool_set_config ()
gboolean | gst_buffer_pool_set_active ()
gboolean | gst_buffer_pool_is_active ()
void | gst_buffer_pool_set_flushing ()
GstFlowReturn | gst_buffer_pool_acquire_buffer ()
void | gst_buffer_pool_release_buffer ()

## Types and Values

| GstBufferPool
struct | GstBufferPoolClass
enum | GstBufferPoolAcquireFlags
struct | GstBufferPoolAcquireParams

## Object Hierarchy

        GObject
        ╰── GInitiallyUnowned
            ╰── GstObject
                ╰── GstBufferPool

## Includes

    #include <gst/gst.h>

## Description

A GstBufferPool is an object that can be used to pre-allocate and recycle buffers of the same size and with the same properties.

A GstBufferPool is created with `gst_buffer_pool_new()`.

Once a pool is created, it needs to be configured. A call to `gst_buffer_pool_get_config()` returns the current configuration structure from the pool. With `gst_buffer_pool_config_set_params()` and `gst_buffer_pool_config_set_allocator()` the bufferpool parameters and allocator can be configured. Other properties can be configured in the pool depending on the pool implementation.

A bufferpool can have extra options that can be enabled with `gst_buffer_pool_config_add_option()`. The available options can be retrieved with `gst_buffer_pool_get_options()`. Some options allow for additional configuration properties to be set.

After the configuration structure has been configured, `gst_buffer_pool_set_config()` updates the configuration in the pool. This can fail when the configuration structure is not accepted.

After the a pool has been configured, it can be activated with `gst_buffer_pool_set_active()`. This will preallocate the configured resources in the pool.

When the pool is active, `gst_buffer_pool_acquire_buffer()` can be used to retrieve a buffer from the pool.

Buffers allocated from a bufferpool will automatically be returned to the pool with `gst_buffer_pool_release_buffer()` when their refcount drops to 0.

The bufferpool can be deactivated again with `gst_buffer_pool_set_active()`. All further `gst_buffer_pool_acquire_buffer()` calls will return an error. When all buffers are returned to the pool they will be freed.

Use `gst_object_unref()` to release the reference to a bufferpool. If the refcount of the pool reaches 0, the pool will be freed.

## Functions

### GST_BUFFER_POOL_IS_FLUSHING()

    #define GST_BUFFER_POOL_IS_FLUSHING(pool)  (g_atomic_int_get (&pool->flushing))

Check if the bufferpool is flushing. Subclasses might want to check the state of the pool in the acquire function.

#### Parameters

pool | a GstBufferPool |

### gst_buffer_pool_new ()

    GstBufferPool *
    gst_buffer_pool_new (void);

Creates a new GstBufferPool instance.

#### Returns

a new GstBufferPool instance.

[transfer floating]

### gst_buffer_pool_config_get_params ()

    gboolean
    gst_buffer_pool_config_get_params (GstStructure *config,
                                       GstCaps **caps,
                                       guint *size,
                                       guint *min_buffers,
                                       guint *max_buffers);

Get the configuration values from `config` .

#### Parameters

config | a GstBufferPool configuration. | [transfer none]
caps | the caps of buffers. | [out][transfer none][allow-none]
size | the size of each buffer, not including prefix and padding. | [out][allow-none]
min_buffers | the minimum amount of buffers to allocate. | [out][allow-none]
max_buffers | the maximum amount of buffers to allocate or 0 for unlimited. | [out][allow-none]

#### Returns

`TRUE` if all parameters could be fetched.

### gst_buffer_pool_config_set_params ()

    void
    gst_buffer_pool_config_set_params (GstStructure *config,
                                       GstCaps *caps,
                                       guint size,
                                       guint min_buffers,
                                       guint max_buffers);

Configure `config` with the given parameters.

#### Parameters

config | a GstBufferPool configuration |
caps | caps for the buffers |
size | the size of each buffer, not including prefix and padding |
min_buffers | the minimum amount of buffers to allocate. |
max_buffers | the maximum amount of buffers to allocate or 0 for unlimited. |

### gst_buffer_pool_config_validate_params ()

    gboolean
    gst_buffer_pool_config_validate_params
                                   (GstStructure *config,
                                    GstCaps *caps,
                                    guint size,
                                    guint min_buffers,
                                    guint max_buffers);

Validate that changes made to `config` are still valid in the context of the expected parameters. This function is a helper that can be used to validate changes made by a pool to a config when `gst_buffer_pool_set_config()` returns `FALSE`. This expects that `caps` haven't changed and that `min_buffers` aren't lower then what we initially expected. This does not check if options or allocator parameters are still valid, won't check if size have changed, since changing the size is valid to adapt padding.

#### Parameters

config | a GstBufferPool configuration. | [transfer none]
caps | the excepted caps of buffers. | [transfer none]
size | the expected size of each buffer, not including prefix and padding |
min_buffers | the expected minimum amount of buffers to allocate. |
max_buffers | the expect maximum amount of buffers to allocate or 0 for unlimited. |

#### Returns

`TRUE`, if the parameters are valid in this context.

Since: 1.4

### gst_buffer_pool_config_get_allocator ()

    gboolean
    gst_buffer_pool_config_get_allocator (GstStructure *config,
                                          GstAllocator **allocator,
                                          GstAllocationParams *params);

Get the `allocator` and `params` from `config` .

#### Parameters

config | a GstBufferPool configuration. | [transfer none]
allocator | a GstAllocator. | [transfer none]
params | GstAllocationParams |

#### Returns

`TRUE`, if the values are set.

### gst_buffer_pool_config_set_allocator ()

    void
    gst_buffer_pool_config_set_allocator (GstStructure *config,
                                          GstAllocator *allocator,
                                          const GstAllocationParams *params);

Set the `allocator` and `params` on `config` .

One of `allocator` and `params` can be `NULL`, but not both. When `allocator` is `NULL`, the default allocator of the pool will use the values in `param` to perform its allocation. When `param` is `NULL`, the pool will use the provided `allocator` with its default GstAllocationParams.

A call to `gst_buffer_pool_set_config()` can update the allocator and params with the values that it is able to do. Some pools are, for example, not able to operate with different allocators or cannot allocate with the values specified in `params` . Use `gst_buffer_pool_get_config()` to get the currently used values.

#### Parameters

config | a GstBufferPool configuration |
allocator | a GstAllocator. | [allow-none]
params | GstAllocationParams. | [allow-none]

### gst_buffer_pool_config_n_options ()

    guint
    gst_buffer_pool_config_n_options (GstStructure *config);

Retrieve the number of values currently stored in the options array of the `config` structure.

#### Parameters

config | a GstBufferPool configuration |

#### Returns

the options array size as a guint.

### gst_buffer_pool_config_add_option ()

    void
    gst_buffer_pool_config_add_option (GstStructure *config,
                                       const gchar *option);

Enabled the option in `config` . This will instruct the `bufferpool` to enable the specified option on the buffers that it allocates.

The supported options by `pool` can be retrieved with `gst_buffer_pool_get_options()`.

#### Parameters

config | a GstBufferPool configuration |
option | an option to add |

### gst_buffer_pool_config_get_option ()

    const gchar *
    gst_buffer_pool_config_get_option (GstStructure *config,
                                       guint index);

Parse an available `config` and get the option at `index` of the options API array.

#### Parameters

config | a GstBufferPool configuration |
index | position in the option array to read |

#### Returns

a gchar of the option at `index` .

### gst_buffer_pool_config_has_option ()

    gboolean
    gst_buffer_pool_config_has_option (GstStructure *config,
                                       const gchar *option);

Check if `config` contains `option` .

#### Parameters

config | a GstBufferPool configuration |
option | an option |

#### Returns

`TRUE` if the options array contains `option` .

### gst_buffer_pool_get_options ()

    const gchar **
    gst_buffer_pool_get_options (GstBufferPool *pool);

Get a `NULL` terminated array of string with supported bufferpool options for `pool` . An option would typically be enabled with `gst_buffer_pool_config_add_option()`.

#### Parameters

pool | a GstBufferPool |

#### Returns

a `NULL` terminated array of strings.

[array zero-terminated=1][transfer none]

### gst_buffer_pool_has_option ()

    gboolean
    gst_buffer_pool_has_option (GstBufferPool *pool,
                                const gchar *option);

Check if the bufferpool supports `option` .

#### Parameters

pool | a GstBufferPool |
option | an option |

#### Returns

`TRUE` if the buffer pool contains `option` .

### gst_buffer_pool_get_config ()

    GstStructure *
    gst_buffer_pool_get_config (GstBufferPool *pool);

Get a copy of the current configuration of the pool. This configuration can either be modified and used for the `gst_buffer_pool_set_config()` call or it must be freed after usage.

#### Parameters

pool | a GstBufferPool |

#### Returns

a copy of the current configuration of `pool` . use `gst_structure_free()` after usage or `gst_buffer_pool_set_config()`.

[transfer full]

### gst_buffer_pool_set_config ()

    gboolean
    gst_buffer_pool_set_config (GstBufferPool *pool,
                                GstStructure *config);

Set the configuration of the pool. If the pool is already configured, and the configuration haven't change, this function will return `TRUE`. If the pool is active, this method will return `FALSE` and active configuration will remain. Buffers allocated form this pool must be returned or else this function will do nothing and return `FALSE`.

`config` is a GstStructure that contains the configuration parameters for the pool. A default and mandatory set of parameters can be configured with `gst_buffer_pool_config_set_params()`, `gst_buffer_pool_config_set_allocator()` and `gst_buffer_pool_config_add_option()`.

If the parameters in `config` can not be set exactly, this function returns `FALSE` and will try to update as much state as possible. The new state can then be retrieved and refined with `gst_buffer_pool_get_config()`.

This function takes ownership of `config` .

#### Parameters

pool | a GstBufferPool |
config | a GstStructure. | [transfer full]

#### Returns

`TRUE` when the configuration could be set.

### gst_buffer_pool_set_active ()

    gboolean
    gst_buffer_pool_set_active (GstBufferPool *pool,
                                gboolean active);

Control the active state of `pool` . When the pool is inactive, new calls to `gst_buffer_pool_acquire_buffer()` will return with `GST_FLOW_FLUSHING`.

Activating the bufferpool will preallocate all resources in the pool based on the configuration of the pool.

Deactivating will free the resources again when there are no outstanding buffers. When there are outstanding buffers, they will be freed as soon as they are all returned to the pool.

#### Parameters

pool | a GstBufferPool |
active | the new active state |

#### Returns

`FALSE` when the pool was not configured or when preallocation of the buffers failed.

### gst_buffer_pool_is_active ()

    gboolean
    gst_buffer_pool_is_active (GstBufferPool *pool);

Check if `pool` is active. A pool can be activated with the `gst_buffer_pool_set_active()` call.

#### Parameters

pool | a GstBufferPool |

#### Returns

`TRUE` when the pool is active.

### gst_buffer_pool_set_flushing ()

    void
    gst_buffer_pool_set_flushing (GstBufferPool *pool,
                                  gboolean flushing);

Enable or disable the flushing state of a `pool` without freeing or allocating buffers.

#### Parameters

pool | a GstBufferPool |
flushing | whether to start or stop flushing |

Since: 1.4

### gst_buffer_pool_acquire_buffer ()

    GstFlowReturn
    gst_buffer_pool_acquire_buffer (GstBufferPool *pool,
                                    GstBuffer **buffer,
                                    GstBufferPoolAcquireParams *params);

Acquire a buffer from `pool` . `buffer` should point to a memory location that can hold a pointer to the new buffer.

`params` can be `NULL` or contain optional parameters to influence the allocation.

#### Parameters

pool | a GstBufferPool |
buffer | a location for a GstBuffer. | [out]
params | parameters. | [transfer none][allow-none]

#### Returns

a GstFlowReturn such as `GST_FLOW_FLUSHING` when the pool is inactive.

### gst_buffer_pool_release_buffer ()

    void
    gst_buffer_pool_release_buffer (GstBufferPool *pool,
                                    GstBuffer *buffer);

Release `buffer` to `pool` . `buffer` should have previously been allocated from `pool` with `gst_buffer_pool_acquire_buffer()`.

This function is usually called automatically when the last ref on `buffer` disappears.

#### Parameters

pool | a GstBufferPool |
buffer | a GstBuffer. | [transfer full]

## Types and Values

### GstBufferPool

    typedef struct _GstBufferPool GstBufferPool;

The structure of a GstBufferPool. Use the associated macros to access the public variables.

### struct GstBufferPoolClass

    struct GstBufferPoolClass {
      GstObjectClass    object_class;

      const gchar ** (*get_options)    (GstBufferPool *pool);
      gboolean       (*set_config)     (GstBufferPool *pool, GstStructure *config);

      gboolean       (*start)          (GstBufferPool *pool);
      gboolean       (*stop)           (GstBufferPool *pool);

      GstFlowReturn  (*acquire_buffer) (GstBufferPool *pool, GstBuffer **buffer,
                                        GstBufferPoolAcquireParams *params);
      GstFlowReturn  (*alloc_buffer)   (GstBufferPool *pool, GstBuffer **buffer,
                                        GstBufferPoolAcquireParams *params);
      void           (*reset_buffer)   (GstBufferPool *pool, GstBuffer *buffer);
      void           (*release_buffer) (GstBufferPool *pool, GstBuffer *buffer);
      void           (*free_buffer)    (GstBufferPool *pool, GstBuffer *buffer);
      void           (*flush_start)    (GstBufferPool *pool);
      void           (*flush_stop)     (GstBufferPool *pool);
    };

The GstBufferPool class.

#### Members

GstObjectClass `object_class`; | Object parent class |
`get_options` () | get a list of options supported by this pool |
`set_config` () | apply the bufferpool configuration. The default configuration will parse the default config parameters |
`start` () | start the bufferpool. The default implementation will preallocate min-buffers buffers and put them in the queue |
`stop` () | stop the bufferpool. the default implementation will free the preallocated buffers. This function is called when all the buffers are returned to the pool. |
`acquire_buffer` () | get a new buffer from the pool. The default implementation will take a buffer from the queue and optionally wait for a buffer to be released when there are no buffers available. |
`alloc_buffer` () | allocate a buffer. the default implementation allocates buffers from the configured memory allocator and with the configured parameters. All metadata that is present on the allocated buffer will be marked as GST_META_FLAG_POOLED and GST_META_FLAG_LOCKED and will not be removed from the buffer in `reset_buffer` . The buffer should have the GST_BUFFER_FLAG_TAG_MEMORY cleared. |
`reset_buffer` () | reset the buffer to its state when it was freshly allocated. The default implementation will clear the flags, timestamps and will remove the metadata without the GST_META_FLAG_POOLED flag (even the metadata with GST_META_FLAG_LOCKED). If the GST_BUFFER_FLAG_TAG_MEMORY was set, this function can also try to restore the memory and clear the GST_BUFFER_FLAG_TAG_MEMORY again. |
`release_buffer` () | release a buffer back in the pool. The default implementation will put the buffer back in the queue and notify any blocking acquire_buffer calls when the GST_BUFFER_FLAG_TAG_MEMORY is not set on the buffer. If GST_BUFFER_FLAG_TAG_MEMORY is set, the buffer will be freed with `free_buffer` . |
`free_buffer` () | free a buffer. The default implementation unrefs the buffer. |
`flush_start` () | enter the flushing state. (Since 1.4) |
`flush_stop` () | leave the flushign state. (Since 1.4) |

### enum GstBufferPoolAcquireFlags

Additional flags to control the allocation of a buffer

#### Members

GST_BUFFER_POOL_ACQUIRE_FLAG_NONE | no flags |
GST_BUFFER_POOL_ACQUIRE_FLAG_KEY_UNIT | buffer is keyframe |
GST_BUFFER_POOL_ACQUIRE_FLAG_DONTWAIT | when the bufferpool is empty, acquire_buffer will by default block until a buffer is released into the pool again. Setting this flag makes acquire_buffer return GST_FLOW_EOS instead of blocking. |
GST_BUFFER_POOL_ACQUIRE_FLAG_DISCONT | buffer is discont |
GST_BUFFER_POOL_ACQUIRE_FLAG_LAST | last flag, subclasses can use private flags starting from this value. |

### struct GstBufferPoolAcquireParams

    struct GstBufferPoolAcquireParams {
      GstFormat                 format;
      gint64                    start;
      gint64                    stop;
      GstBufferPoolAcquireFlags flags;
    };

Parameters passed to the `gst_buffer_pool_acquire_buffer()` function to control the allocation of the buffer.

The default implementation ignores the `start` and `stop` members but other implementations can use this extra information to decide what buffer to return.

#### Members

GstFormat `format`; | the format of `start` and `stop` |
gint64 `start`; | the start position |
gint64 `stop`; | the stop position |
GstBufferPoolAcquireFlags `flags`; | additional flags |

## See Also

GstBuffer