[gmpi] Re: Topic 6: Time representation
- From: Tim Hockin <thockin@xxxxxxxxxx>
- To: gmpi@xxxxxxxxxxxxx
- Date: Wed, 30 Apr 2003 14:29:37 -0700 (PDT)
> 1.) The host defines a quanta which is the smallest time interval
> allowed in its timing system. This is communicated to the plugin at the
> time of instantiation, and cannot change for a particular instance of a
> plugin. The host communicates this using an int64 quanta per second value.
Mike - it seems that we've entered an area not common for audio, so bear
with me:
1) Can you not just increase the sampling rate?
2) how does quanta/sec relate to samples/sec ? Audio plugins will want to
generate data at the audio sampling rate. Can we say then that quanta are
really sub-samples, and are defined as sub-samples per sample, with audio
generated at the sample rate? Pure-audio hosts will set the subsample rate
to 1, and the sample rate to 44100 or 48000 or whatever.
> 2.) All timestamps used in GMPI are int64 values using the quanta
> defined by the host.
Yes, I think we all agree on that, now.
> 3.) When an event is timestamped, it contains 2 timestamps: the absolute
> time since start, and the transport time. For hosts with no transport,
> these two values are identical.
I don't see the need to timestamp it with transport time - transport time is
potentially non-linear, and may even loop or stop altogether.
> 4.) Musical meter events are timestamped using the same timestamp type.
> The plugin can request to be passed to it at any integer division of a
> reference 4/4 bar. So if the plugin ask for a resolution of 16, then it
> will receive 16 meter events during a 4/4 measure, 5 meter events in a
> 5/16 bar, 10 in a 5/8 bar, and so on.
useful, perhaps
> Every meter event contains its metrical position and its duration in
> quanta to the next event. So if you ask for a resolution of 2 and the
> meter is 3/8, you will receive two meter events, one at the beginning of
> the measure with a duration of 2 eighth notes (expressed in quanta), and
> 1 after 2 eighth notes with a duration of 1 eighth note. Therefore all
> tempo changes are quantized by the host to the resolution requested by
> the plugin.
I don't get this. How does the host know how to quantize like this.
Better, perhaps to just get a BEAT event and subdivide that internally. But
if plugins start relying on this, then we have to assume we send meter
events when the transport is stopped, which is weird..
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