[LV2] Dynamic manifest URIs and CAPS' strange case

David Robillard d at drobilla.net
Fri Feb 1 14:20:23 PST 2013

On Fri, 2013-02-01 at 23:48 +0200, Stefano D'Angelo wrote:
> Hi all,
> Next NASPRO release is coming soon, no new features, just small fixes
> here and there.
> Anyway, I still have two potentially tricky things to sort out. The
> first is whether it matters if I change URIs of dynamic manifests (not
> bridged plugins, just the dman:DynManifest). The problem is that
> NASPRO is not part of Atheme anymore and that is also reflected by the
> website having been moved to sourceforge. Hopefully nobody is
> hardcoding the old URIs.

I would be quite surprised if that's the case and changing the URI of
the DynManifest breaks anything.

> Secondly, and probably more importantly, I have the feeling that the
> new CAPS release keeps the old LADSPAs unique IDs but breaks port
> signatures. This sucks, I remember me and David suggesting the author
> not to do it, but still he seems to have done it. This means current
> bridges are propagating the breakage into LV2 land. Which sucks even
> more because it explicitly violates LV2 rules. Now, probably the best
> thing to do would be to special case CAPS and try to detect whether
> it's the new or old version being bridged and use new URIs for the new
> plugin set (something like urn:ladspa:caps-new:XXXX?). However, it
> might happen again in the future, I guess. Any suggestions?

Honestly I wouldn't bother.  While this sucks, and if true is a very bad
move whether you consider LV2 or not, I don't think NASPRO should
attempt to add layers upon layers of compatibility kludges for specific
plugin sets.  If anything not having the straightforward URI mapping any
more would probably cause even more difficulties.

Assuming this is a problem, i.e. the port signatures have changed
incompatibly, that breaks existing sessions for LADSPA supporting hosts,
too.  They broke in LADSPA, and they will consequently break in LV2.  A
shame, but an unavoidable one.  Particularly since no hosts that I know
of actually implement any kind of graceful compatibility break tolerance
for LV2 plugins, I would say the expected behaviour is to simply wrap
the LADSPA, and worrying about this is not worth the effort.

Since LADSPA authors are likely to just blame LV2 as an easy out, it's
probably more effective to argue based on LADSPA host sessions anyway.
For example, if you had an Ardour session that uses that plugin, that
session is now broken.  This is a very bad thing.

... but it's not NASPRO's place to deal with it, IMO.


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