[LAD] ladspa: what does LADSPA_PROPERTY_REALTIME mean?

Paul Davis paul at linuxaudiosystems.com
Wed Sep 9 21:07:54 UTC 2015


My interpretation is that LV2 means LADSPA Version 2 and thus should
be preferred at all times to LADSPA.

On Wed, Sep 9, 2015 at 4:56 PM, IOhannes m zmölnig <zmoelnig at iem.at> wrote:
> hi richard, paul, stefan and fellow LADders,
>
> the Debian folks currently are a bit at a loss of the proper
> interpretation of the LADSPA_PROPERTY_REALTIME property.
>
> ladspa.h says:
>> /* Property LADSPA_PROPERTY_REALTIME indicates that the plugin has a
>>    real-time dependency (e.g. listens to a MIDI device) and so its
>>    output must not be cached or subject to significant latency. */
>
> the discussion started about a year ago (see [760758]), and it seems
> that there are two opposing interpretations of that property:
>
>
> #1 setting the property indicates to the host, that the plugin must not
> be used in a non-realtime environment.
> this means that a plugin that has this property set, must not be used
> for batch processing, e.g. because it uses wall-clocked input (like
> MIDI-devices) that simply won't deliver proper input when running at a
> speed that is decoupled from wall clock.
>
> OR
>
> #2 setting the property indicates to the host, that the plugin can be
> run at a lower (timing) priority; so the host can deliberately add
> latency without compromising the usefulness of the full processing
> chain. that would be mostly for plugins that do not do any input ->
> output processing, but only take input (e.g. metering, recording).
>
>
>
> that's just a quick summary. there's more arguments in the bugreport
> [760758].
>
> personally i lean towards #1 (as i don't see much use cases for the
> second interpretation), but given that someone as deeply involved into
> linux audio as fons favours #2, i would like to ask the creators of
> LADSPA for their canonical view.
>
>
> thanks for your insights,
>
> gfmadsr
> IOhannes
>
>
>
> [760758] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=760758
>
>
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