Re: Default ChannelLayout's
Re: Default ChannelLayout's
- Subject: Re: Default ChannelLayout's
- From: Derk-Jan Hartman <email@hidden>
- Date: Fri, 3 Jun 2005 12:44:37 +0200
On 03 jun 2005, at 10:53, Jean-Alexis Montignies wrote:
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.
I meant "Should VLC for".
Remember that this is not about channel reordering, it is about VLCs
auhal output module having to detect which speakerconfiguration a user
has. These things are completely different.
auhal layout != vlc auhal output module speaker detection.
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?
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.
That's irrelevant. That's a workaround. i'm not interested in those
things. it doesn't matter if VLC currently mix the LFE into the 2 front
speakers, it's that it COULD want to do that. This is actually a
regular feature request we have and we might want to implement that in
the future.
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.
Yes and VLC does do this, it is just that by default there is no
audioChannelLayout set on a device...apparently.
For instance look at line 132 of this debug output:
http://pastebin.com/294240
You can see here:
https://trac.videolan.org/vlc/browser/trunk/modules/audio_output/
auhal.c?rev=11253 how VLCs auhal output module retrieves this
information.
The debug is from a Yamaha device. The channel ID's are not correctly
set by default. Apparently no Layout is set at all, otherwise the
If you go into Audio Midi Setup it shows dolby 5.1 layout and correctly
positioning of speakers. Click apply and done just to be sure.
VLC still gets -1 unknown identification of the channel.
The users puts speakers in the wrong order. clicks apply, goes back to
the correct settings, clicks apply, clicks done, now VLC does retrieve
the proper speaker configuration and the auhal module CAN retrieve the
proper speaker ID's for the channels.
Notice that currently i use kAudioDevicePropertyPreferredChannelLayout
to do this and get this information fromt he device driver and not from
the auhal unit itself. Perhaps this is a wrong assumption, but i
believe that last time i was experimenting with this, a correct setting
for the auhal unit on the output side was not available.
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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---
Universiteit Twente
Derk-Jan Hartman (d.hartman at student.utwente dot nl)
http://www.sidequest.org
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