Re: Default ChannelLayout's
Re: Default ChannelLayout's
- Subject: Re: Default ChannelLayout's
- From: Jean-Alexis Montignies <email@hidden>
- Date: Fri, 3 Jun 2005 10:53:24 +0200
On 3 juin 05, at 08:44, Derk-Jan Hartman wrote:
I have succeeded in creating the auhal module for VLC.
A test version is available here:
http://episteme.arstechnica.com/eve/ubb.x/a/tpc/f/8300945231/m/
403005733731/r/994001763731#994001763731
Now my question is on ChannelLayout
https://trac.videolan.org/vlc/browser/trunk/modules/audio_output/
auhal.c?rev=11253
VLC uses this to discover which speakers are connected, so it can
make decisions about for instance downmixing a dolby C channel into
the L and R channels if you only have Stereo available.
Now it seems that as far as i can tell ALL setups do not know this
themselves. You need to explicitly set this in Audio Midi Setup
Util. Even worse it seems that even if it shows correctly in Audio
Midi Setup util, you need to explicitly CHANGE, apply, change BACK
and again apply to get this set.
There for i would like to know the following.
1: Does VLC for default # of channels make assumptions about which
speaker setup is used?
This is not related to core audio, but as far as I remember, it was
coreaudio.c vlc module which was doing the assumptions and give the
other layers the layout.
2: I'm looking at the util, and it basically says CoreAudio only
accepts, 5.1 6.1 7.1 Quadrophonic (2Front 2Rrear), Hexagonal( L R C
Ls Rs Rc ) and Octogonal.
Does this imply that in case of a 4 channel device, Coreaudio will
expect a Quad (2F2R) setup? and not something like 3front + LFE
setup? Does it also imply that in a 6 channel setup vlc will assume
5.1 before 6.0 ? Does it also imply that if you have a 5.0 setup
that you are just out of luck in CoreAudio?
Unfortunately yes. For now the AudioMidiSetup utility only allows
definitions for the formats you describe. The CoreAudio structures
however supports the other formats.
That would be a feature request for the coreaudio team: allow
AudioMidiSetup to present more speaker configuration choices.
Now vlc as far as I know don't submix the LFE channel, at least for a52.
You can define a 5.1 layout, and connect only 5 speakers as a
workaround.
Now VLC should not assume the available speakers from the count of
the channels, but read that from the layout. This is the
responsibility of the auhal vlc module. I can take a look at the code
if is commited, as I already modified this in an old version of vlc.
This would of course be unfortunate because in the case of 5.0 VLC
would like to have mixed LFE into the 2 Front speakers for
instance. And if it's not possible to explain this to Audio Midi
Setup util then VLC can never know this LFE channel is not
connected and should be downmixed.
DJ
Jean-Alexis Montignies
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