Application Loopback Sample is unable to record from Microsft Teams App

[lmengnr]

I wanted to try making a system recording application based on the application loopback sample provided by windows classic samples. But I have observed that this code works for all processes but is unable to record from the Microsoft teams app.

I also asked a question on stack overflow: https://stackoverflow.com/questions/79832526/wasapi-application-loopback-is-unable-to-record-ms-teams

My goal is to use process loopback (via AUDIOCLIENT_ACTIVATION_TYPE_PROCESS_LOOPBACK) so that I can capture the system mix through the Windows audio engine.

In my main use case I want to record audio from all applications except my own app, so I’m using PROCESS_LOOPBACK_MODE_EXCLUDE_TARGET_PROCESS_TREE. I have also tested with PROCESS_LOOPBACK_MODE_INCLUDE_TARGET_PROCESS_TREE just to rule that out.

What Works

Using the ApplicationLoopback approach with VIRTUAL_AUDIO_DEVICE_PROCESS_LOOPBACK, my capture app successfully records audio for:

• Slack
• Zoom
• Google Meet in Chrome/Edge
• Microsoft Teams meetings in a browser (Edge/Chrome)
• Youtube videos in the browser

On all of these, the output WAV contains valid audio as expected.

What Fails

The problem is only with the Microsoft Teams desktop application (ms-teams.exe):

• With process loopback (ApplicationLoopback-style):
  • The recording has the correct duration and format.
  • But the audio buffer is effectively all zeros (silence) whenever the audio source is a Teams desktop meeting.

Multiple Output streams for Microsoft Teams

One strange thing I have observed is that the Microsoft teams app has two output streams shown.

I wrote a small diagnostic tool that enumerates audio sessions for a given process using IAudioSessionManager2 and reads the peak levels via IAudioMeterInformation.

For the output device used by Teams during a meeting, I see the following:

• Two render sessions for ms-teams.exe on the same render device, plus one capture session.
• Both render sessions:
  • Have the same process ID (ms-teams.exe).
  • Show non-zero peak and average levels while meeting audio is playing.
  • Often have identical or very similar metering values.

For example (simplified sample output):

// Source - https://stackoverflow.com/q/79832526
// Posted by fahdIm
// Retrieved 2025-12-03, License - CC BY-SA 4.0

Session [0]:
  Session GUID:     {0.0.0.00000000}.{6474f13d-839f-4be8-b36c-f653233effdd}|\Dev...
  Grouping GUID:    {C82CDF72-3957-4B52-ABF2-9ACA5F8153A1}
  Samples w/ Audio: 32 / 50 (64%)
  Max Peak Level:   49.6552%
  Avg Peak Level:   12.5515%
  *** THIS SESSION HAS SIGNIFICANT AUDIO ACTIVITY ***

Session [1]:
  Session GUID:     {0.0.0.00000000}.{6474f13d-839f-4be8-b36c-f653233effdd}|\Dev...
  Grouping GUID:    {C82CDF72-3957-4B52-ABF2-9ACA5F8153A1}
  Samples w/ Audio: 32 / 50 (64%)
  Max Peak Level:   49.6552%
  Avg Peak Level:   12.642%
  *** THIS SESSION HAS SIGNIFICANT AUDIO ACTIVITY ***

I also wrote a session enumerator which lists all audio sessions opened for a device and it also shows the same thing:

// Source - https://stackoverflow.com/q/79832526
// Posted by fahdIm
// Retrieved 2025-12-03, License - CC BY-SA 4.0

=== Render Devices ===
Speakers (Realtek(R) Audio) [48000 Hz, 32-bit, 2 ch (Float)] : 0 active sessions
  ID: {0.0.0.00000000}.{357dc357-13e3-4cdb-90c9-ab54f23dedcf}
XG27ACS (Intel(R) Display Audio) [48000 Hz, 32-bit, 2 ch (Float)] : 0 active sessions
  ID: {0.0.0.00000000}.{4af2ff2a-e7bf-4a47-8de4-876e9ba2d6ce}
Speakers (Razer BlackShark V2 HS 2.4) [48000 Hz, 32-bit, 2 ch (Float)] [Default: Console, Multimedia, Communications] : 2 active sessions
  ID: {0.0.0.00000000}.{6474f13d-839f-4be8-b36c-f653233effdd}
  - ms-teams.exe PID: 10596
  - ms-teams.exe PID: 10596
CABLE Input (VB-Audio Virtual Cable) [48000 Hz, 32-bit, 2 ch (Float)] : 0 active sessions
  ID: {0.0.0.00000000}.{65fbe74c-81c9-4c39-8a75-55033aa39f4c}
CABLE In 16ch (VB-Audio Virtual Cable) [48000 Hz, 32-bit, 2 ch (Float)] : 0 active sessions
  ID: {0.0.0.00000000}.{a2a0ed57-95c3-4689-b0ff-efabb8c3efe1}

For all other apps like Slack, Zoom, Chrome, etc., I only see one render session per process on the same device in this scenario. Even if I have multiple videos playing on YouTube or through a media player like VLC, I always see only one stream per process. Here's a sample of 2 VLC sessions playing audio running simultaneously, you can see that 2 different processes:

=== Render Devices ===
Headphones (OnePlus Buds 3) [48000 Hz, 32-bit, 2 ch (Float)] [Default: Console, Multimedia, Communications] : 2 active sessions
  ID: {0.0.0.00000000}.{19c0ada4-d680-46a9-919c-dca80bee9807}
  - vlc.exe PID: 7100
  - vlc.exe PID: 5984

Device loopback works for Microsoft teams

I have observed that the device loopback ( https://learn.microsoft.com/en-us/windows/win32/coreaudio/loopback-recording ) can successfully capture the output audio from the Microsoft teams app.

What I’ve checked

• Multiple machines (different manufacturers, different audio hardware): same behavior.
• Different Teams versions, including at least 25306.804.4102.7193 (and slightly earlier versions): same behavior.

Repro steps

• Start a Teams desktop meeting with remote audio playing.
• Run the ApplicationLoopback sample targeting ms-teams.exe (both include and exclude modes tested).
• Check the recorded wav file, the audio will be silent.
• Repeat with Slack/Zoom/Chrome → WAV has valid audio.