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[Bug 20698] Need way to determine "performance.now()" time of current audio output

From: <bugzilla@jessica.w3.org>
Date: Tue, 02 Apr 2013 19:35:17 +0000
To: public-audio@w3.org
Message-ID: <bug-20698-5429-5B12cUMqLW@http.www.w3.org/Bugs/Public/>
https://www.w3.org/Bugs/Public/show_bug.cgi?id=20698

--- Comment #5 from Joe Berkovitz / NF <joe@noteflight.com> ---
Ehsan, let me clarify the needs here with respect to the latency between the
context's currentTime and the signal coming out of the sound card.

High accuracy for this use case is not needed. It's OK for screen updates to be
slightly delayed for the purposes of seeing a cursor or pointer whose position
over some sort of waveform or notated music reflects what one is hearing. These
visual delays will not become really bothersome until they are consistently
over 75ms or so.  And typically the DOM-to-screen display delay is much, much
lower (more like the 16ms number you gave).

On the other hand these delays can be dwarfed by the currentTime-to-sound-card
latency on some platforms, which can be as high as 200 or 300 ms. Having the
cursor be misplaced by that amount is an experience-killer. That's why it's so
important for an application to be able to acquire this number from the API:
it's potentially much larger.

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