[Bug 20698] Need a way to determine AudioContext time of currently audible signal


--- Comment #23 from Joe Berkovitz / NF <joe@noteflight.com> ---
Capturing discussion from the WG conference call 4/25/2013:

- Need to document that currentTime represents the time at which the next
sample block to be synthesized by the node graph will be played.

- Need to document that currentTime advances (for an non-offline context)
roughly in real time, not just monotonically.  In other words, the clock-time
derivative of currentTime is approximately 1.

- Will introduce a new read-only attribute on AudioContext that exposes a
"presentation latency" as described in the initial comment for this bug. This
latency is not an absolute guarantee, it just includes all predictable latency
contributions known to the implementation. On Android <= 4.0, for instance,
this latency would expose the roughly .25 second delay imposed by the platform.

- AC will expose a function converting from currentTime units to
high-resolution DOM performance time.

- AC will expose an inverse function converting from high-resolution DOM
performance to currentTime units.

An additional note that was not discussed:

- Corollary: need to document (if this is true) that currentTime advances
monotonically by a time quantum equal to the block size, as each block is
synthesized.  This is important because if true it implies that
ScriptProcessingNode JS code may consult currentTime instead of
event.playbackTime, and that the latter is no longer needed since it's always
equal to currentTime.

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Received on Thursday, 25 April 2013 17:18:35 UTC