Gst.Meta¶

Fields¶

Name	Type	Access	Description
flags	`Gst.MetaFlags`	r/w	extra flags for the metadata
info	`Gst.MetaInfo`	r/w	pointer to the `Gst.MetaInfo`

Methods¶

class	`api_type_aggregate_params` (api, aggregated_params, params0, params1)
class	`api_type_get_tags` (api)
class	`api_type_has_tag` (api, tag)
class	`api_type_register` (api, tags)
class	`api_type_set_params_aggregator` (api, aggregator)
class	`deserialize` (buffer, data, size)
class	`get_info` (impl)
class	`register_custom` (name, tags, transform_func, *user_data)
class	`register_custom_simple` (name)
	`compare_seqnum` (meta2)
	`get_seqnum` ()
	`serialize` (data)
	`serialize_simple` (data)

Details¶

class Gst.Meta¶

The Gst.Meta structure should be included as the first member of a Gst.Buffer metadata structure. The structure defines the API of the metadata and should be accessible to all elements using the metadata.

A metadata API is registered with Gst.Meta.api_type_register() which takes a name for the metadata API and some tags associated with the metadata. With Gst.Meta.api_type_has_tag() one can check if a certain metadata API contains a given tag.

Multiple implementations of a metadata API can be registered. To implement a metadata API, gst_meta_register() should be used. This function takes all parameters needed to create, free and transform metadata along with the size of the metadata. The function returns a Gst.MetaInfo structure that contains the information for the implementation of the API.

A specific implementation can be retrieved by name with Gst.Meta.get_info().

See Gst.Buffer for how the metadata can be added, retrieved and removed from buffers.

classmethod api_type_aggregate_params(api, aggregated_params, params0, params1)[source]¶

Parameters:

api (GObject.GType) – the GObject.GType of the API for which the parameters are being aggregated.
aggregated_params (Gst.Structure) – This structure will be updated with the combined parameters from both params0 and params1.
params0 (Gst.Structure) – a Gst.Structure containing the new parameters to be aggregated.
params1 (Gst.Structure) – a Gst.Structure containing the new parameters to be aggregated.

Returns:

True if the parameters were successfully aggregated, False otherwise.

Return type:

bool

When a element like tee decides the allocation, each downstream element may fill different parameters and pass them to Gst.Query.add_allocation_meta(). In order to keep these parameters, a merge operation is needed. This aggregate function can combine the parameters from params0 and param1, and write the result back into aggregated_params.

New in version 1.26.

classmethod api_type_get_tags(api)[source]¶

Parameters:: api (GObject.GType) – an API
Returns:: an array of tags as strings.
Return type:: [str]

New in version 1.2.

classmethod api_type_has_tag(api, tag)[source]¶

Parameters:

api (GObject.GType) – an API
tag (int) – the tag to check

Returns:

True if api was registered with tag.

Return type:

bool

Check if api was registered with tag.

classmethod api_type_register(api, tags)[source]¶

Parameters:

api (str) – an API to register
tags ([str]) – tags for api

Returns:

a unique GObject.GType for api.

Return type:

GObject.GType

Register and return a GObject.GType for the api and associate it with tags.

classmethod api_type_set_params_aggregator(api, aggregator)[source]¶

Parameters:

api (GObject.GType) – the GObject.GType of the API for which the aggregator function is being set.
aggregator (Gst.AllocationMetaParamsAggregator) – the aggregator function to be associated with the given API type.

This function sets the aggregator function for a specific API type.

New in version 1.26.

classmethod deserialize(buffer, data, size)[source]¶

Parameters:

buffer (Gst.Buffer) – a Gst.Buffer
data (int) – serialization data obtained from Gst.Meta.serialize()
size (int) – size of data

Returns:

the metadata owned by buffer, or None.

consumed:: total size used by this meta, could be less than size

Return type:

(Gst.Meta or None, consumed: int)

Recreate a Gst.Meta from serialized data returned by Gst.Meta.serialize() and add it to buffer.

Note that the meta must have been previously registered by calling one of gst_*_meta_get_info () functions.

consumed is set to the number of bytes that can be skipped from data to find the next meta serialization, if any. In case of parsing error that does not allow to determine that size, consumed is set to 0.

New in version 1.24.

classmethod get_info(impl)[source]¶

Parameters:: impl (str) – the name
Returns:: a Gst.MetaInfo with impl, or None when no such metainfo exists.
Return type:: Gst.MetaInfo or None

Lookup a previously registered meta info structure by its implementation name impl.

classmethod register_custom(name, tags, transform_func, *user_data)[source]¶

Parameters:

name (str) – the name of the Gst.Meta implementation
tags ([str]) – tags for api
transform_func (Gst.CustomMetaTransformFunction or None) – a Gst.MetaTransformFunction
user_data (object or None) – user data passed to transform_func

Returns:

a Gst.MetaInfo that can be used to access metadata.

Return type:

Gst.MetaInfo

Register a new custom Gst.Meta implementation, backed by an opaque structure holding a Gst.Structure.

The registered info can be retrieved later with Gst.Meta.get_info() by using name as the key.

The backing Gst.Structure can be retrieved with Gst.CustomMeta.get_structure(), its mutability is conditioned by the writability of the buffer the meta is attached to.

When transform_func is None, the meta and its backing Gst.Structure will always be copied when the transform operation is copy, other operations are discarded, copy regions are ignored.

New in version 1.20.

classmethod register_custom_simple(name)[source]¶

Parameters:: name (str) – the name of the Gst.Meta implementation
Returns:: a Gst.MetaInfo that can be used to access metadata.
Return type:: Gst.MetaInfo

Simplified version of Gst.Meta.register_custom(), with no tags and no transform function.

New in version 1.24.

compare_seqnum(meta2)[source]¶

Parameters:: meta2 (Gst.Meta) – a Gst.Meta
Returns:: a negative number if self comes before meta2, 0 if both metas have an equal sequence number, or a positive integer if self comes after meta2.
Return type:: int

Meta sequence number compare function. Can be used as GLib.CompareFunc or a GLib.CompareDataFunc.

New in version 1.16.

get_seqnum()[source]¶

Return type:: int

Gets seqnum for this meta.

New in version 1.16.

serialize(data)[source]¶

Parameters:: data (Gst.ByteArrayInterface) – Gst.ByteArrayInterface to append serialization data
Returns:: True on success, False otherwise.
Return type:: bool

Serialize self into a format that can be stored or transmitted and later deserialized by Gst.Meta.deserialize().

This is only supported for meta that implements Gst.MetaInfo.serialize_func, False is returned otherwise.

Upon failure, data->data pointer could have been reallocated, but data->len won’t be modified. This is intended to be able to append multiple metas into the same GLib.ByteArray.

Since serialization size is often the same for every buffer, caller may want to remember the size of previous data to preallocate the next.

New in version 1.24.

serialize_simple(data)[source]¶

Parameters:: data (bytes) – GLib.ByteArray to append serialization data
Returns:: True on success, False otherwise.
Return type:: bool

Same as Gst.Meta.serialize() but with a GLib.ByteArray instead of Gst.ByteArrayInterface.

New in version 1.24.