[linux-audio-dev] XAP and Event Outputs

[David Olofson]

On Tuesday 10 December 2002 15.54, Steve Harris wrote:
> On Tue, Dec 10, 2002 at 09:14:36 -0500, Paul Davis wrote:
> > >So time starts at some point decided by the host.  Does the host
> > > pass the current timestamp to process(), so plugins know what
> > > time it is?  I assume that if the host loops, or the user jumps
> > > back in song-position, time does not jump with it, it just
> > > keeps on ticking?
> > >
> > >I guess my only question is how do plugins know what time it is
> > > now?
> >
> > in VST and JACK, its done with a function call that retrieves a
> > struct containing current time info, including both transport,
> > sample and musical positions, amongst other things.
>
> We want this as well (to allow MTC and MIDI Clock sync if nothing
> else), but the timestamp stuff needs to be monotonic, samples
> synced, and I guess it makes sense to pass it in with process().

Yes. Event/audio time is one thing, and musical time is something 
completely different, although related.

Musical time can be a bit hairy to calculate, so I don't think it's a 
good idea to do it all the time, and pass it to all plugins. That 
could be acceptable if you did it by publishing a struct in the host 
struct - but who is interested in the musical time of the first 
sample frame in the buffer? There's nothing special about that sample 
frame.

What you want is a callback that gives you the musical time 
corresponding to a timestamp, and probably a few other variants as 
well. (Timestamp is only good for "short range", since the host 
cannot know how many wraps back or ahead you mean, and so has to 
assume that you want the one in [now-2G, now+2G].)


//David Olofson - Programmer, Composer, Open Source Advocate

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