[linux-audio-dev] XAP: a polemic

David Olofson david at olofson.net
Sun Dec 15 21:55:25 UTC 2002


On Monday 16 December 2002 03.16, Paul Davis wrote:
> >> >this is the best suggestion so far. i love callbacks. note that
> >> >"meter" includes both tempo and time signature. you knew that,
> >> > though. i can't see anyone wanting to use TIME_TICKS.
> >> >
> >> >--p
> >>
> >> Callbacks do make sense here, I agree.
> >
> >I disagree. Callbacks are not sample accurate.
>
> i was assuming that the callback would be executed so that it was
> passed the audio frame at which the change occurs.

Ah, I see. Well, that would work, but how fun is that when there are 
multiple changes per block? Why not just use the event system, when 
it's there anyway? Less overhead, and implementing the changes at the 
right positions in the block becomes trivial.


> >Either way, the only callback I see in that proposal is the host
> > one to "register" for these events... Did I miss something?
>
> my definition of callback:
>
>    register_callback (function_to_be_called_when, when_to_call_it);
>
> the name "callback" is based on a style of telephone interaction:
>
> no callbacks:
>
>      Paul: hi David, is audiality is available?
>      David: its not.
>
> with callbacks:
>
>      Paul: hi David, please call me back at +1 610-667-4807
> 	      when audiality is available.
>
>    [ ... time passes ... ]
>    [ ... david calls ... ]
>
>      David: its available.
>
> or alternatively:
>
>      David: it will be available in 5 minutes.

Well, I need more than 5 minutes for the next release - but I get the 
idea. :-)

Now, I'd just say that timestamped events are really rather similar. 
They've got the advantages of the "it will be available in 5 minutes" 
version (no need to split buffers - whatever that would mean in 
telephony terms), but it's as easy to implement as the "its 
available" variant, both for senders and receivers.


//David Olofson - Programmer, Composer, Open Source Advocate

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