[LV2] Buffersize, Options and Externtion-Data

[Robin Gareus]

On 09/10/2015 03:50 AM, David Robillard wrote:
> That said, there is a case for this value being used for optimization,
> so here you go:
> 
> http://lv2plug.in/git/cgit.cgi/lv2.git/commit/?id=930649e812dc1b03f21be5ef7f412d892d3add1b

https://github.com/Ardour/ardour/commit/09caf8336f4ec681668a940e7df00ec18b3fd836


To conclude this..

Plugins that previously expected maxBufferLength to be the "current", or
assumed that the "max" can change over the lifetime of a plugin instance
should be updated.

LV2-host authors, please update the host at your convenience if it
supports the buffersize extension.


In short:

Host:
 * [optionally] provide min/maxBufferLength to the Plugin as
instantiation option

 * [optionally] provide a opts:interface as extension_data, and set()
the buffersize whenever the block-size of the host changes.


Plugins:
 * if the plugin's run() function cannot cope with arbitrary
sample-counts, fail to instantiate if the host does not provide
min/maxBufferLength information.

 * if the run() function needs to know the current blocksize, implement
an option inteface. The host will call opts_iface->set() in
non-realtime context and block processing until the plugin returns.

Also check during instantiation if the host supports the extension and
fail to instantiate if the DSP depends on it (ideally the DSP
implementation won't need it, but that's a different story).


Cheers!
robin