Why do you need the virtual render endpoint? It would be simpler to have your
app give the networked voice data to your driver via a backchannel, and then
third-party apps can pick it up from your virtual capture endpoint.
From: wdmaudiodev@xxxxxxxxxxxxxx<mailto:wdmaudiodev@xxxxxxxxxxxxxx>
Sent: Monday, October 19, 2020 8:55 AM
To: wdmaudiodev@xxxxxxxxxxxxx<mailto:wdmaudiodev@xxxxxxxxxxxxx>
Subject: [EXTERNAL] [wdmaudiodev] Virtual Audio Passthrough Driver - data
format conversion?
Hi everyone,
Tim Roberts over at the osr.com forum has been very kind in answering my audio
driver questions over the last few months. Recently, he referred me to this
mailing list where "all the cool audio driver kids, including several very
helpful members of the Microsoft audio team, hang out".
My goal is to play networked voice data (in our app) to a virtual render
endpoint, and have it 'loop-back' to a virtual capture endpoint that 3rd-party
chat apps like Skype, Zoom, etc. can consume.
My audio driver prototype is based on SYSVAD/WaveRT. Besides being newer and
recommended in the docs, WaveRT handles more of the copying data to/from the
DMA buffers. My hope was that I could write less code and have a more stable
driver.
What's needed is just a straight-through audio pipe, so I tried using a single,
common buffer for render & capture streams; keeping the respective
PlayPositions in sync. For this to have a hope of working, both render and
capture streams would have to be identical in terms of format (e.g. channels,
frames/sec). Alas, when I tested, each stream had significant differences in
their PCM format (channels, frame rate). I'm still testing to see if I can
limit/coerce both endpoints to the same format: a single channel at some
arbitrary 'good enough' frame rate, but this approach is starting to look
uncomfortably fragile.
My second prototype is based upon MSVAD/WaveCyclic. With WaveCyclic, I
implement the DMA buffer copying logic, so I can do whatever data conversion is
required. I'm aware of a few other 'virtual audio driver' projects on Github
with similar goals; all based upon WaveCyclic.
I wanted to see how they dealt with the data format conversion issue, but when
I look at their CopyTo and CopyFrom implementations, I don't see them dealing
with conversion at all. There doesn't appear to be any code (e.g. in
DataRangeIntersection) that limits streams to a specific number of channels or
frame-rate.
Can anyone shed light on this?
I'm sure my expectations must be off somehow, but it seems to me that some kind
of conversion must be required when copying data between streams of
sufficiently different format...
