We should also add the port latency, but there's currently no way to ensure
it's synchronized with the ringbuffer (the ringbuffer will update before the
port latency gets updated).
A few notes about it:
The OpenAL device's requested buffer metrics are ignored, and instead the
device will keep one JACK-sized buffer's worth of audio prepared for JACK's
next process request.
Output is restricted to 32-bit float stereo. Part of this is because JACK
requires a buffer size that's a power of 2 (measured in samples), and the
ringbuffer requires a buffer size that's a power of 2 (measured in bytes). A
channel count of 6 (5.1) or 7 (6.1) will not work without causing a sample to
split over the edge of the ringbuffer. Additioanlly, JACK doesn't provide
information about what channel configuration a device or set of ports has, so
there's no way to know what ports 3 and up map to (even the first two ports are
unknown, but assuming stereo seems to work well enough).
There is no device latency measurement (for AL_SOFT_source_latency) due to the
non-atomicity between the ringbuffer's read size and port latency. A method is
needed to ensure the ringbuffer's read size and port latency can both be
measured between the end of a JACK update cycle (when the port latency has been
updated with the newly-retrieved audio) and the following ringbuffer read
update.
Apparently, 5.1 surround sound is supposed to use the "side" channels, not the
back channels, and we've been wrong this whole time. That means the "5.1 Side"
is actually the correct 5.1 setup, and using the back channels is anomalous.
Additionally, this means the 5.1 buffer format should also use the the side
channels instead of the back channels.
A final note: the 5.1 mixing coefficients are changed so both use the original
5.1 surround sound set (with the surround channels at +/-110 degrees). So the
only difference now between 5.1 "side" and 5.1 "back" is the channel labels.
OpenAL's capture API guarantees the application gets the format requested, or
else the device will fail to open. The only valid change is that the capture
buffer can be larger than requested.
