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Re: Routing QT audio to an AudioUnit

From: "Alberto Ricci" <email@hidden>
> Is there any way to route audio playback coming from a QuickTime
> movie to an AudioUnit?
>
> I am afraid that the different methods used to convey samples (a push
> mechanism in QT, a pull mechanism for AudioUnits) make it too
> complicated.
>
> However, I suppose that many applications would benefit from being
> able to, say, filter a QT movie controller's output using some AU
> which provides greater flexibility than MediaSetSoundBassAndTreble()
> ;-) , or making the audio flow into the 3D Mixer for spatialization,
> and so on.
>
> Maybe it is something Apple engineers could think about...

Indeed. We should talk off-line about everything you are trying to do, as I
am doing some major (future) work in QuickTime's handling of audio right
now. You certainly _should_ be able to do this sort of thing in the future.

> In the meantime, I wonder which solutions can be found. I can only think
of:

> - setting the movie's sound output device to a custom component,
> which implements a ring buffer. This buffer is shared with an
> AudioUnit which can "pull" samples from it.

This would work, assuming that new versions of QuickTime continue to play
audio to a Sound Output Device. I can certainly imagine a future where that
wouldn't be the case... ;-) There's a fine Sound Output sample on our
website somewhere that simply writes the audio to a file. Substitute ring
buffer for file, and you're on your way.

> - subclassing a MovieController so that it disables any sampled sound
> tracks; then it installs an action filter proc in order to be
> notified of any transport state modification. An AudioUnit would read
> samples using QT API calls from the movie, making sure it keeps
> itself in sync with the movie controller and any transport action
> performed by the user...

Yeesh. That sounds really hard and overly complex, especially for a
solution that I hope will only be a temporary workaround.

Didn't I meet you at WWDC? You were playing a movie while it was being
recorded into.

Greg Chapman
QuickTime Engineering
email@hidden
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References: 
 >Routing QT audio to an AudioUnit (From: Alberto Ricci <email@hidden>)



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