Re: HALOutputUnit (Pt 1)
Re: HALOutputUnit (Pt 1)
- Subject: Re: HALOutputUnit (Pt 1)
- From: William Stewart <email@hidden>
- Date: Wed, 14 Jan 2004 14:20:36 -0800
Well, for a device that has both input and output (like FW devices,
builtin audio), you use the same unit. Thus, you only have one output
unit in a graph and some AU in your graph is going to make a connection
to this output unit's output on element 1.
For a device (like USB) that doesn't have both in and out, other
approaches have to be taken.
Essentially, as you describe below (though I wouldn't necessarily add
the input side to its own graph... rather, I'd just have the input
being pulled from a buffer where you've written the input data too. A
bit complicated, but we are working on something to simplify this
somewhat... Details to come at a later stage
Bill
On 13/01/2004, at 12:43 PM, James Coker wrote:
I haven't looked at the input callbacks yet, but have to agree that
having a standard solution that will cover most cases for an AUGraph
w/ both input and output would be nice. I'm guessing that the current
best approach would be to use two HALOutputUnits -- one (in it's own
AUGraph) for input and one (in a second AUGraph) for output, with
an appropriate buffer in between to feed data from one to the other.
Jim
On Jan 13, 2004, at 7:03 AM, Robert Grant wrote:
Just a final clarification - would it be OK to use the
SetInputCallback approach for reading audio from all HAL devices
(both uni and bi-directional)? I don't think it would but I'm just
trying to see if there's a "once size fits all" approach?
Thanks,
Robert.
On Jan 12, 2004, at 11:04 PM, James Coker wrote:
Does this imply that all, or almost all USB audio devices will have
this setup?
Jim
On Jan 12, 2004, at 7:33 PM, Jeff Moore wrote:
Yes this is true. The USB spec doesn't require that the input side
of a device be clocked the same as the output side. They can even
be running at different sample rates and still be adhering to the
spec. From the HAL's point of view, the two sides of the device
represent two separate clock sources. Therefore the HAL publishes
them as separate devices through the API.
On Jan 12, 2004, at 5:54 PM, Robert Grant wrote:
Thanks a lot Bill - that clarifies things tremendously. And I
think I now know why Audio In from the HALOutputUnit was not
working for me a while back - I'm using a USB Audio I/O device and
I guess that shows up as two separate Audio Devices?
Robert.
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