[LAD] "enhanced event port" LV2 extension proposal

David Olofson david at olofson.net
Sat Dec 1 20:49:37 UTC 2007

On Saturday 01 December 2007, Dave Robillard wrote:
> Taking a step back, it would be nice to have these events (being
> generic) able to use something other than frame timestamps, for
> future dispatching/scheduled type event systems.

I'm not sure about the scope of this LV2 event system, but the idea of 
using timestamps related to anything other than audio time (ie 
buffers, sample frames etc) seems to be a violation of the idea that 
events are essentially structured control data or similar - ie 
anything that's "locked" to the audio stream.

The only valid reason I can see for using an unrelated timebase for 
timestamps is when the timestamps can only be translated to actual 
(audio) time by the receiving plugin. This is an interesting concept, 
but how to use it properly in the context of an event system where 
the event transport is based on the "one buffer per buffer cycle" 
idea? Sure; you can just send events and assume that the receiver 
will queue them internally as needed, but how does the sender know 
how far ahead it needs to be to avoid events arriving late? (If it 
knows the audio/timestamp relation, why use non audio related 
timestamps in the first place?)

I just don't see how this can work; not in a real time system. Either 
you need to deal with exactly one buffer at a time - and then you may 
as well use audio based timestamps at all times - or you need some 
sort of random access event system or something.

> (This may sound a bit esoteric, but to do something like Max right,
> you need absolute time stamps).

What does max do that requires this, and how does it actually work? 
I'm probably missing the point here...


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

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