Re: CAClock and MIDI Clock
Re: CAClock and MIDI Clock
- Subject: Re: CAClock and MIDI Clock
- From: Doug Wyatt <email@hidden>
- Date: Fri, 10 Oct 2008 09:30:53 -0700
On Oct 10, 2008, at 7:34 , Evan Olcott wrote:
I think I see an inherent conflict with "time keeps moving" like
you're saying above and starting and stopping clock. The messages
are indeed bracketed by start/stop messages, but as soon as there's
a MIDI endpoint to send to, the clock rolls right on out and doesn't
stop. Isn't MIDI clock supposed to stop sending after a stop
message? Or am I wrong? I could have sworn I read that that's how
it's supposed to be interpreted...
No ... I take back what I wrote late last night (sorry) ... the F8
clock messages are being sent all the time. From the MIDI 1.0 Detailed
Specification: "If Timing Clocks (F8H) are sent during idle time they
should be sent at the current tempo setting of the transmitter even
while it is not playing. Receivers which are slaved to incoming Real
Time messages ... can thus phase lock their internal clocks while
waiting for a Start (FAH) or Continue (FBH) command."
If the F8's aren't sent before starting, then the receiver won't
necessarily have any idea of how fast to play when it starts.
Additionally, how do I tell the CAClock the difference between a
"start" message and a "continue" message to send when I call
CAClockStart? It seems to just sorta "know", but what if I want to
start at the beginning? Does that have to do with CASetCurrentTime?
The MIDI spec says that Start signifies the beginning of the song or
sequence. In CAClock terms, that means position 0 on the media
timeline. I believe the implementation will send Start when that's
where it's starting from; Continue otherwise.
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