Re: Simple 3D mixer confusion
Re: Simple 3D mixer confusion
- Subject: Re: Simple 3D mixer confusion
- From: Stephen Davis <email@hidden>
- Date: Wed, 5 May 2004 17:44:09 -0700
If you're shipping a commercial app, this is a definite no-no. AC-3
implementations exist in the wild but they are not licensed by Dolby
and using them in a commercial app is asking for a world of hurt.
The 2-channel AC-3 licensing terms were fairly decent in the past but
the CPU load for 5.1 is pretty expensive and so is the license. Dolby
_may_ have recently loosened the licensing structure for AC-3 since it
is the codec for HDTV but I don't think so. If you're serious about
more than experimentation, I would recommend contacting Dolby.
stephen
On May 5, 2004, at 5:07 PM, John Stiles wrote:
OK, I've done a little more Googling and it looks like there are some
freebie AC3 encode libraries (http://essej.net/ac3jack/). So that's
not a big issue. The CPU load for doing something like this doesn't
seem practical for a game, though.
If someone wanted to make a quick buck, they could try wiring AC3Jack
into CoreAudio and getting the system to see it as a new output device
(i.e. selectable in the Sound control panel or Audio MIDI Setup). Then
all these G5 owners with optical outs could mess with 5.1 sound in any
app that supports multi-channel. Although most people would probably
turn it off in applications with heavy CPU requirements, it would be a
really cool toy. But I don't think it's the answer for me :)
On May 5, 2004, at 4:33 PM, Jeff Moore wrote:
Given a library that implements an AC-3 encoder, one could easily
wrap it up in an AudioCodec. This would make it useable by the
AudioConverter. There aren't any technical impediments to someone
bringing such a beast up. However, my impression is that AC-3
encoding in software is expensive in terms of CPU cost and there is
the issue of licensing (about which I know little). My point is that
applications can implement this stuff if it is important to them.
There are no technical barriers erected by the system.
The difference I think you perceive (and why you stated the optical
port is going to waste) is that on Windows, the audio device does the
AC-3 encoding in hardware and stuffs it out the optical port. This is
why it is cheap on Windows. So far, I don't know of any audio devices
that support Mac OS X that do this. Again there aren't any technical
barriers to keep hardware developers from implementing AC-3 encoding.
So far, none have for whatever reason. Looks like another market
opportunity to me.
On May 5, 2004, at 4:06 PM, John Stiles wrote:
On May 5, 2004, at 3:37 PM, Jeff Moore wrote:
What a shame that the optical out on the G5 is going to waste.
I don't know if it's being wasted or not being fully utilized by
applications. For instance, what's stopping you from putting an
AC-3 encoder in your games to encode the mixed audio prior to
handing it to the HAL?
Last I heard, this involved a per-seat licensing cost and a heavy
CPU burden, but I don't know how current that info is.
If it's cheap (from a licensing standpoint), cheap (from a CPU
standpoint), and there's an AudioUnit that can do the conversion,
I'd be more than happy to drop that in the code and be done with it.
Is this idea actually doable?
--
Jeff Moore
Core Audio
Apple
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