14 Dec
2002
14 Dec
'02
1:54 a.m.
1. getTimeInfo() does *not* take a time argument of any kind;
only a 32 bit filter, to say which fields you actually need.
That is, you can only get the full info for the start of
the buffer. There is a tempoAt() call, that gives you the
tempo at the specified sample frame in the buffer.
2. The VstTimeInfo struct is interesting. I like the unit
for musical time: pulses with 1 PPQN. :-) Tempo is in
BPM. (Why not QN/s? ;-) There is a field that says where
the last bar starts. There's also time signature, SMPTE,
MIDI clock (samples to next clock) and a bunch of flags.
Flags include transport changed, playing and "cycle
active". (The latter come with loop start and end positions,
obviously.) And automation reading + writing... It is also
interesting to note that the "sample position" field in
here is timeline bound - it may jump! There's a nanoseconds
field as well, holding the "system time" corresponding to
the first sample in the buffer.
Conclusion:
a. The information is there, but you have to *pull*
it from the host. Doesn't seem like you're ever
notified about tempo changes or transport events.
b. Since you're asking the host, and there are no
other arguments, there is no way that one plugin
can keep track of more than one timeline. It
seems that it is assumed that there is only one
timeline in a net.
3. There are calls that allow plugins to get the audio input
and output latency.
Conclusion:
c. I'm assuming that this is mostly useful for
VU-meters and other stuff that needs to be
delayed appropriately for correct display.
Obviously not an issue when the audio latency
is significantly shorter than the duration of
one video frame on the monitor! ;-) Seriously
though, this is needed for "high latency"
applications to display meters and stuff
correctly. They're not very helpful if they're
half a second early!
4. There is a feature that allows plugins to tell the host
which "category" they would fit in. (There is some
enumeration for that somewhere.) Might be rather handy
when you have a large number of plugins installed...
5. A getCurrentProcessLevel() host call lets the plugin ask
what kind of context it's being called from. Can return
values corresponding to "not supported", "user/GUI",
"audio/irq", "sqeuncer/irq" and "user/offline". Other
values are possible and "probably" (as they say) mean
something that pre-empts the user thread.
6. There is support for using the whole process() call
asynchronously. This is for external DSPs and stuff. The
plugin is expected to return "instantly" from process(),
and then the host wanders off to do something else. The
host will use another plugin call to poll, to see if the
data from the external DSP (or whatever) is available.
Conclusion:
d. I think we can ignore this feature. We don't
do external DSP, and we don't feel like having
hosts poll/busy-wait for data, do we...?
7. There's a bunch of calls specifically meant for off-line
processing. This is basically about accessing the host's
"open" files, setting markers and stuff, being notified
when files are opened, closed, changed, when markers are
changed etc. A plugin API in itself.
8. You can ask the host about the speaker arrangement,
for surround stuff...
9. There is a bypass feature, so that hosts can have
plugins implement sensible bypass for mono -> surround
and other non-obvious in/out relations. (As if in/out
relations ever were to be assumed "obvious"!)
10.Finally, the states. There are 2 calls related to this;
suspend() and resume(). Nothing much is said about these,
and they're not used for much in the examples. Just for
clearing delay buffers and the like. Memory is generally
allocated in the constructors and freed in the destructors,
but I'm not sure when and where you're supposed to
reallocate buffers if you need to... (This is when you
start realizing why compatibility problems with VST are
so common. Where are the reference docs!? *heh*)
//David Olofson - Programmer, Composer, Open Source Advocate
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