[MPlayer-users] Mac OS X Audio 5.1 Channel Output Problems

[Ulion]

2008/1/17, galenz at zinkconsulting.com <galenz at zinkconsulting.com>:
>
> On Jan 17, 2008, at 2:07 AM, Reimar Döffinger wrote:
>
> > Hello,
> > On Thu, Jan 17, 2008 at 01:45:40AM -0800, galenz at zinkconsulting.com
> > wrote:
> > [...]
> >> However, this is extremely un-Mac like and un-intuitive, given the
> >> available data. The Apple audio API automatically detects the number
> >> of channels physically available. The macosx audio out module should
> >> pass this value along to mplayer and set the number of channels
> >> accordingly.
> >
> > I am not aware that there are any sound cards that can detect
> > whether 2,
> > 4, 6 or 8 speakers are connected to them. Does Apple have some special
> > hardware there?
>
> Apple only does stereo audio out with their analog hardware. They have
> never shipped a Mac with more than one analog audio out port. This
> allows them to avoid the scenario where it is uncertain how many
> speakers are connected. Read below for more details.
>
> >> This is what I mean about mplayer not detecting the multple channels.
> >> Various other applications - such as QuickTime Player and VLC - rely
> >> upon detecting available channels in this manner and make audio
> >> conversion/output settings accordingly.
> >
> > I'm almost certain that they behave exactly like MPlayer with
> > channels=6
> > at the expense of giving wrong output for those who only connect two
> > speakers then.
>
> Using Apple hardware, it is only possible to output >2 channels using
> a digital (optical) link. All x86-based Macs (and many newer PowerPCs)
> - including notebooks - have a hidden optical audio out inside their
> stereo analog jack (via mini TOS link connector.) This digital link is
> all auto-detected and everything is handled with extraordinary elegance.
>
> Third party hardware can provide other configurations involving analog
> out (which cannot be reliably detected), but by default, adding new
> analog hardware only uses 2 channel audio out. Normally, 5.1 and 7.1
> configurations are setup using Audio MIDI Setup. Then you can simply
> choose between various outputs as the "primary" in the Sound system
> preference - built-in stereo, third party stereo, 5.1, 7.1, etc.
>
> Given that using Apple hardware, the system handles auto-detection
> perfectly, and the system has excellent system-level configuration for
> third party hardware that cannot auto-detect, applications are
> normally expected to utilize all available channels, should they have
> content suitable for said channels.
>
> Given my experience with every other Mac application behaving like
> this, my natural assumption was that mplayer failed to properly detect
> the channels, hence my (in retrospect) rather stupid question. In
> fact, it was just un-intuitive behavior. It would be worth changing
> this in mplayer, as there are basically no scenarios where it will
> cause problems, but many scenarios where it will confuse users who are
> accustomed to the behavior of all other applications on their system.

I think mplayer did not auto-detect output channal layout (that's what
you configured in the MIDI panel) on any platform.
Although it's useful if there's such auto-detect function, but
currently mplayer's arch seems not easy to support it.

-- 
Ulion