This extension defines a facility for plugins to get information about the block length (the sample_count parameter of LV2_Descriptor::run) and port buffer sizes, as well as several features which can be used to restrict the block length. The host provides access to all the relevant information via the bufsz:access feature. To require restrictions on the block length, plugins can require additional features: bufsz:boundedBlockLength, bufsz:powerOf2BlockLength, and bufsz:fixedBlockLength. These features are data-only, that is they merely indicate a restriction and do not carry any data or API.
The feature that provides access to buffer size information. This feature is the only one in this extension which carries data: to implement it the host passes a feature with URI LV2_BUF_SIZE__access and an LV2_Buf_Size_Access for data, which provides functions the plugin can call to investigate the buffer size.
A feature that indicates the host will provide a minimum and maximum block length via LV2_Buf_Size_Access::get_sample_count(). Plugins that copy data from audio inputs can require this feature to ensure they know how much space is required for auxilliary buffers. Note the minimum may be zero, this feature is mainly useful to ensure a maximum is available. All hosts SHOULD support this feature, since it is simple to support and necessary for plugins to create auxiliary buffers.
A feature that indicates the host will always call LV2_Descriptor::run() with the same value for sample_count. If available, LV2_Buf_Size_Access::get_sample_count() must report this value for both min and max. Note that requiring this feature may severely limit the number of hosts capable of running the plugin.
A feature that indicates the host will always call LV2_Descriptor::run() with a power of two sample_count. If available, LV2_Buf_Size_Access::get_sample_count() must report this value for both min and max. Note this feature does not guarantee the value is the same each call, to ensure that the plugin must require both this feature and bufsz:fixedBlockLength. Note that requiring this feature may severely limit the number of hosts capable of running the plugin.