直接渲染到 WASAPI 时，两个流之一中没有音频 output

Question

I've been stuck on this problem for weeks now and Google is no help, so hopefully some here can help me.

I am programming a software sound mixer in C++, getting audio packets from the network and Windows microphones, mixing them together as PCM, and then sending them back out over the network and to speakers/USB headsets. This works. I have a working setup using the PortAudio library to handle the interface with Windows. However, my supervisors think the latency could be reduced between this software and our system, so in an attempt to lower latency (and better handle USB headset disconnects) I'm now rewriting the Windows interface layer to directly use WASAPI. I can eliminate some buffers and callbacks doing this, and theoretically use the super low latency interface if that's still not fast enough for the higher ups.

I have it only partially working now, and the partially part is what is killing me here. Our system has the speaker and headphones as three separate mono audio streams. The speaker is mono, and the headset is combined from two streams to be stereo. I'm outputting this to windows as two streams, one for a device of the user's choice for speaker, and one of another device of the user's choice for headset. For testing, they're both outputting to the default general stereo mix on my system.

I can hear the speaker perfectly fine, but I cannot hear the headset, no matter what I try. They both use the same code path, they both go through a WMF resampler to convert to 2 channel audio at the sample rate Windows wants. But I can hear the speaker, but never the headset stream.

It's not an exclusive mode problem: I'm using shared mode on all streams, and I've even specifically tried cutting down the streams to only the headset, in case one was stomping the other or something, and still the headset has no audio output.

It's not a mixer problem upstream, as I haven't modified any code from when it worked with PortAudio streams. I can see the audio passing through the mixer and to the output via my debug visualizers.

I can see the data going into the buffer I get from the system, when the system calls back to ask for audio. I should be hearing something , static even, but I'm getting nothing. (At one point, I bypassed the ring buffer entirely and put random numbers directly into the buffer in the callback and I still got no sound.)

What am I doing wrong here? It seems like Windows itself is the problem or something, but I don't have the expertise on Windows APIs to know what, and I'm apparently the most expert for this stuff in my company. I haven't even looked yet as to why the microphone input isn't working, and I've been stuck on this for weeks now. If anyone has any suggestions, it'd be much appreciated.

Answer 1

Check the re-sampled streams: output the stereo stream to the speaker, and output the mono stream to the handset.

Use IAudioClient::IsFormatSupported to check supported formats for the handset.

Verify your code using an mp3 file. Use two media players to play different files with different devices simultaneously.