Subject: Re: [linux-audio-dev] App intercomunication issues, some views.
From: Paul Davis (pbd_AT_op.net)
Date: Tue Jul 23 2002 - 21:01:30 EEST
>> >Why not have a seperate API/daemon for MIDI and
>> >have it and JACK both use the same UST timestamps?
>>
>> you can\'t use any timestamp unless its derived from the clock master,
>> which UST by definition almost never is. the clock on your PC doesn\'t
>> run in sync with an audio interface, and will lead to jitter and drift
>> if used for general timing.
>
>The mapping between UST and audio time (frames) is continuously updated.
>There is no need for the UST to be the master clock. If JACK would
UST = Unadjusted System Time
I haven't seen any implementations of UST where you could specify a
different source of the clock tick than the system clock/cycle timer.
>audio by scheduling it on UST. An application doing JACK audio output
>and MIDI output would most likely estimate the UST for the output buffer
>using the UST of the input buffer and schedule MIDI messages for that
>buffer in the callback also. So this then looks much like your proposal.
>But there is also still the ability to use send MIDI messages for
>immediate transmission.
Well, thats actually what we have in JACK already, if the client uses
the ALSA sequencer in another (non-JACK) thread. its precisely the
design i have in my head for Ardour, for example.
>Using UST would also enable syncing to video or some other media
>stream without it all residing in the same API.
Something has to connect the UST to the applications, and I have not
seen anything in the definition of UST that would put UST in user
space.
--p
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