[gmpi] Re: Topic 7: Audio packaging
- From: Tim Hockin <thockin@xxxxxxxxxx>
- To: gmpi@xxxxxxxxxxxxx
- Date: Wed, 21 May 2003 13:47:37 -0700 (PDT)
> one buffer per audio channel. And since any pin may have N
I hate the notion of 'pins' having multiple channels. I prefer to think of
it as one audio-channel per wire. Think of a typical setup with a bunch of
mono patch cables - one channel == one patch cable.
> But we also need metadata about what multi-channel audio format is
> being represented (mono, stereo, LtRt, M-S, quad, 5.1, 7.1, etc.),
> with corresponding channel order/number conventions, so that the plug
> can know what to do with each channel buffer. I.e. there needs to be
> an enum or other shorthand tag for representing the
For XAp we did this: The plugin hints each channel with common hints (LEFT,
RIGHT, MONO, LFE, etc). The host can then automatically connect a LEFT
output to a LEFT input. If there is confusion, the host might need to ask
the user. This gives us an infinitely flexible way to handle multi-channel
audio. We don't need to code 5.1, 6.1, 7.1, etc into the spec except as
hints.
Each audio channel may have multiple hints, too. For example, a plug that
can do 5.1 or stereo or mono:
1: MONO, LEFT, FRONT-LEFT
2: RIGHT, FRONT-RIGHT
3: CENTER
4: REAR-LEFT
5: REAR-RIGHT
6: LFE
The host then has enough info to do lots of smart things, including showing
the user the localized (based on hint) names.
As for in-place vs not, we can simplify everything by making the API
in-place safe, and forcing plugs that are not safe to use an internal
temporary buffer (allocated by the host). However, with multi-channel
audio, it does get complicated to know which input corresponds to which
output. Perhaps it is simpler to just say that there is never in-place
processing.
Tim
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