Re: M4P through AUHAL to multichannel device (last call)
Re: M4P through AUHAL to multichannel device (last call)
- Subject: Re: M4P through AUHAL to multichannel device (last call)
- From: Austin Shoemaker <email@hidden>
- Date: Fri, 23 Jan 2004 18:50:27 -0800
Kurt Revis has already solved the problem for unprotected content.
There's some great sample code that routes QT audio streams into
CoreAudio.
http://www.snoize.com/
To tackle the general case, I am writing a Cocoa class that bridges
QuickTime to multichannel CoreAudio by registering virtual device
components during runtime and routing the PCM data into the HAL for
specified output streams on the device. This should contribute
minimally to latency- I think this is already how the placeholder sdevs
work.
This will cover .m4a, .m4p, and any other QT sound you can throw at it.
I'll let you know once this is done.
Austin
On Jan 23, 2004, at 5:06 PM, Doug Wyatt wrote:
If it's protected content, then you have to use QuickTime or iTunes to
play the file. But both QuickTime (via SoundManager) and iTunes (via
CoreAudio) respect the default stereo pair you have selected for your
multichannel device -- in Audio MIDI Setup or HALLab.
In fact you can even programmatically change the default stereo pair
using AudioDeviceSetProperty. Or are you wanting to play multiple
protected files through multiple stereo pairs, all at once?
If it's an unprotected .m4a and you want to bypass the Sound Manager,
then you can -- as I am learning how to do today -- open the MP4 file
as a QuickTime movie, find the audio track, find the media, step
through the "interesting times" in the media, which will yield a
series of AAC packets which can be passed through the AudioConverter
to decode them.
There is a little gotcha involving configuring the decoder, but if you
get that far before I do, please ask again.
Doug
On Jan 22, 2004, at 18:25, Austin Shoemaker wrote:
All I want to do is play my music to any stereo pair on my
multichannel output hardware.
The only problem is protected AAC, which is not friends with
CoreAudio.
The only workarounds I have found to be effective are convoluted and
inefficient, and hence not acceptable.
I guess the dust has not settled around the technology line between
QT and CA, and that this niche of functionality (M4P on multichannel
hardware) has been caught in the fringe.
Before I rewrite everything to use QT through sdev components, I
would really appreciate any official comment on this. Especially if
the answer is "I don't know" or "That's right, CoreAudio will not
work", because I really need to know, and I would prefer to choose
CoreAudio as my long-term solution.
Thanks to everyone who has contributed to this inquiry so far.
Sincerely,
Austin
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