Re: GarageBand too clever by half.
Re: GarageBand too clever by half.
- Subject: Re: GarageBand too clever by half.
- From: kelly jacklin <email@hidden>
- Date: Wed, 8 Feb 2006 05:56:11 -0800
On Feb 8, 2006, at 2:02 AM, Ian Kemmish wrote:
I have observed that when GarageBand calls my MusicDevice AU's
Render method, the first three calls have inNumberFrames equal to
1024, and the fourth and subsequent calls have it equal to 256.
Is it expected that calling Render with varying values for
inNumberFrames is a rare or a common thing to happen?
Well, very common in certain cases. For example, if your plugin is
being run downstream of a sample-rate conversion, you will definitely
see varying inNumberFrames values as the SRC either needs more or
fewer sample frames to cover the downstream pull. Usually this
varies by only a couple frames from call to call, except that the
first call will typically ask for more as is needed to prime the SRC
(IIRC).
However, an AU host is free to do divvy up its requests however it
likes as long as it does request a number of samples in excess of the
MaxFramesPerSlice property it has set on your AU. I know of at least
two hosts that will preroll audio before beginning playback, in a
fashion similar to what you are seeing.
In addition, this can vary even more radically if your AU is being
used in an offline fashion (as an export/bounce/render operation),
where the size of requests really need have no correlation to a
regular pull size...
kelly
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