[Bug 743758] osxaudio reports fixed audio capabilities

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=743758
  GStreamer | gst-plugins-good | 1.x

--- Comment #4 from Ilya Konstantinov <ilya.konstantinov at gmail.com> 2015-02-03 11:44:11 UTC ---
(a) I haven't tested yet – not even sure it builds, so that's why I asked not
to commit yet

(b) 

HAL:
Yes, supposedly we can probe formats. This can be done in a separate commit,
though.

Remote IO:
I can't find any API for probing. The input seems happy to provide any
requested format (that can be expressed in ASBD), but only one sample rate (the
session's). I've posted a question about this on coreaudio-api, but so far no
replies:
http://lists.apple.com/archives/coreaudio-api/2015/Feb/msg00000.html

The output is happy to accept any format and any sample rate. It also prefers
the session's sample rate, but will convert as necessary. (Between
GstAudioResample and Core Audio, I'd trust the later to be more effective.)

iOS used to prefer "noninterleaved linear PCM with 8.24-bit fixed-point
samples" (the so-called canonical format) but starting iOS 8 it's obsolete --
see http://asciiwwdc.com/2014/sessions/501:

" ...
So in the past we've had this concept of canonical formats.

And this concept goes back to about 2002 in Mac OS 10.0 or 10.1 or so.

So this format was floating-point, 32-bit, de-interleaved, but then we got
along to iOS, and we couldn't really recommend using float everywhere because
we didn't have the greatest floating-point performance initially.

So for a while canonical was 8.24 fixed-point.

But because of that schism we want to reunite under something new now.

We've deprecated the concept of canonical formats.

Now we have what we call a standard format.

We're back to non-interleaved 32-bit floats on both platforms."

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