[gmpi] Re: Reqs 3.9. Time - opening arguments.1

  • From: Paul Davis <paul@xxxxxxxxxxxxxxxxxxxxx>
  • To: gmpi@xxxxxxxxxxxxx
  • Date: Thu, 05 Feb 2004 13:47:24 -0500

>On Thu, Feb 05, 2004 at 11:29:14AM -0500, Paul Davis wrote:
>> Its still king, but you still need UST to link the two clocks
>> together. You need to know that sample S (more precisely, the first
>> sample of a given process block) "happened" at U1, and that video
>> frame F was drawn at U2, and then you can sync them together.
>
>How does it know what UST time that first sample "happened" at when you the
>sample has not happened until everyone is done processing it AND you can't
>predict the future of UST timing?
>
>You either assign it a UST time in the past, or you need to be able to
>predict UST times (i.e. UST is linear).

notice how i did not define "happened" :)

the UST for the first sample of the process block is obtained by
asking for it at the start of the process cycle. 

providing information on the current "audible" frame is harder, by at
least an order of magnitude, but its in a different problem space
entirely. 

i've been through all this with ardour+JACK recently. this is all
doable, albeit with some important caveats, some of which extend
outside the reach of the computer.

>> Remember: you need to be able to get some time (U1, U2) from a
>> non-process() context (i.e. when doing video sync). Nothing we have in
>> GMPI so far is designed to allow an arbitrary component of a
>> multithreaded plugin to call the host to get "the current sample
>> time", and i don't actually know of any way you could reliably get
>> that anyway.
>
>What is the "current" sample time?  the sample number of the start of the
>current timeslice?  An offset into the current timeslice based on % of
>plugins processed?  The current sample being calculated in the current
>plugin being processed?

Right, you can't define it so easily without references that reach
outside of GMPI. For 99% of all cases, its sample currently emerging
from the connector of a representative physical endpoint in a GMPI
graph.

--p


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