Re: AUHAL output questions
Re: AUHAL output questions
- Subject: Re: AUHAL output questions
- From: William Stewart <email@hidden>
- Date: Fri, 18 Mar 2005 11:14:58 -0800
On 18/03/2005, at 8:05 AM, Derk-Jan Hartman wrote:
Hello all,
Now that I finally have a multichannel device to test VLC (http://
www.videolan.org/vlc) with, I figured that since our audio problems
have been lingering for over 2,5 years now, I'd better fix it myself.
So I was thinking of switching from our current implementation that
uses Coreaudio itself to an AUHAL approach, that is probably less
error prone for us (and also would immediately fix our issues with
multi mono channel devices).
Now i have been trying to get some things clear, but the
information just doesn't seem available.
1: Does AUHAL support cac3 digital streams ?
No - you'd want to have a direct code path to the HAL...
2: If it does. does AUHAL take hoge and non mixing mode
automatically in this case.
3: How do i find out if a device can handle cac3 digital, because
if it can't, it will need to be decoded before being fed to the
audio output core.
It has this in the ASBD's of the streams of the device - it will come
up in the format properties
4: I heard that the AUHAL can do simple conversions. (but no more
than one at a time?)
I'm not sure what you mean. You can give AUHAL *any* pcm format and
it will do the necessary munging to the channels of the device. If
this requires more than one conversion (say int to float and a SRC,
it will do them both)
5: Channel ordering. I have read all the examples and stuff on it,
but what i wanna know is this: channel layout.
for instance VLC (and it works with an edirol device, i'm told, so
that has is as well i guess) seems to have. I have seen little
about this documented.
All you need to do here is the following:
(1) Set the input format (ASBD - oh, and please use
CAStreamBasicDescription in the SDK) providing the number of
channels, etc that you are going to provide to AUHAL
(2) Provide an ACL that specifies the ordering of the channels you
are providing. The number of channels described in the ACL and the
ASBD *must* match.
(3) There is no step 3.. AUHAL will then take whatever the user has
specified in Audio MIDI Setup as their speaker placements, and match
the channels you are providing to those speaker locations.
L R Ls Rs C LFE
aka
kAudioChannelLayoutTag_MPEG_5_1_B
aka
kAudioChannelLayoutTag_DVD_20
where the Sonica Theather has
L R C LFE Ls Rs
aka
kAudioChannelLayoutTag_MPEG_5_1_A
aka
kAudioChannelLayoutTag_ITU_3_2_1
aka
kAudioChannelLayoutTag_DVD_12
You don't have to worry about this - the user configures this in
Audio MIDI Setup, and then AUHAL uses that information as I describe
above
Bill
What is the best way to handle conversion of this?
Can i query the AUHAL for the audiochannel layout?
and can i then use the channel ordering system to reorder the
channels?
DJ
---
Videolan - VLC media player
Derk-Jan Hartman (hartman at videolan dot org)
http://www.videolan.org/vlc
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