Working on synchronization between different inputs to an AUStereoMixer:
Each input buss on the mixer has an AUConverter attached, and the
render call is on the input of the AUConverter.
The time stamp behavior I am observing at the render callback is
somewhat odd:
===
Sometimes, even when the sample rates match across the entire AUGraph
(the streams are all consistent), the render callback on the second
buss will be called after the first, but the time stamp will be earlier:
First buss render callback called: timeStamp = 472 samples (arbitrary)
-then-
Second buss render callback called: timeStamp = 0 samples
This does not happen all the time. Most of the time it is either the
same as the first buss or one buffer later (give or take). Under what
circumstances would this be happening?
===
To make matters a little more complex, if one of the AUConverter's
input sample rates is different (i.e. there is some SR conversion
going on into the mixer), the time stamps seems to not really matter
at all:
First buss render callback called: timeStamp = 77316 samples (arbitrary)
-then-
Second buss (with SR conversion happening) render callback called:
timeStamp = 0 samples
They then increment accordingly to the buffer size (~256, 512,
whatever), but their start times are totally incongruent.
===
What I'd like to be able to do is synchronize the playback of all
these inputs, even if the sample rates are different. However, there
doesn't seem to be any consistency I can reference to make the inputs
work together.
Can I not trust the timeStamp? It seems to be the only way to really
confirm that things will show up at the output AU at the same time,
but if there's no common reference, I can't seem to do it!
Thanks for any guidance on this.
Ev
Technical Knowledge Officer
Head Programmer/Designer
Audiofile Engineering
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