[openal] Querying speaker configuration

Richard Furse richard at blueripplesound.com
Tue Oct 7 05:00:55 EDT 2014

Ah, okay - I've answered completely the wrong question! I think you're saying that OpenAL is basically being used as a wrapper for the operating system audio hardware layer.

Trying to think of alternatives - how is PortAudio looking these days? Does it manage to identify multichannel layouts?

Best wishes,


> -----Original Message-----
> From: openal [mailto:openal-bounces at openal.org] On Behalf Of Chris
> Robinson
> Sent: 07 October 2014 09:45
> To: Richard Furse; 'openal mailing list'
> Subject: Re: [openal] Querying speaker configuration
> On 10/07/2014 01:00 AM, Richard Furse wrote:
> > What's the issue here? Is this the case where there are pre-rendered
> > surround assets and the upstream code wants to choose the right one
> > for the speaker configuration?
> In this case, the game audio is being rendered internally in real-time
> (using a customized version of FMOD's software renderer), and its OpenAL
> backend is used to play the mix to avoid having to code for specific
> sound systems. For this situation, the game would ideally render the
> audio using the same configuration OpenAL is using for output, so it
> acts as close to a pass-through device as it can (e.g. if OpenAL has 5.1
> output, the game's audio would be internally rendered to a 5.1 stream
> and played through a typical source buffer queue using
> AL_FORMAT_51CHN16/32; each input channel would then go to a matching
> output channel). If OpenAL's output configuration is not understood, it
> could just pick a fallback format and let OpenAL up-/down-mix it as needed.
> In some cases there are secondary streams played which OpenAL will need
> to mix too, but the majority of the audio is mixed and rendered internally.
> This is a non-ideal use-case for OpenAL, I know, but for cases like this
> where that's not really possible (it'd be quite a bit of work to fully
> replace FMOD), it can be useful to know the output configuration.
> > BTW, just an instinct, and without looking at the source, the
> > conversation about 5.1 and stereo assets killing each other sounds
> > like a classic "=" which should be a "+=" on a bus. I'm probably
> > wrong, but thought I should mention it in case ;-)
> Yeah, I'm not sure where that could happen, though. The actual mixer
> (where the samples are added together) is the same for all inputs, be it
> mono, stereo, or whatever (each input channel is processed individually,
> using a set of gains for corresponding output channels). That it works
> with two stereo streams, but not a stereo stream and a 5.1 stream,
> suggests to me it's something wrong with the input.
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