Does the new Teams SlimCore client side magic work with MsRdpEx?

[CDSFounder]

Hello,

I am curious to know if you have tested MsRdpEx with the new Teams SlimCore optimization which is replacing the legacy WebRTC for multi media redirection in Teams?

https://learn.microsoft.com/en-us/microsoftteams/vdi-2

The legacy WebRTC worked on Remote Desktop Server and on-prem Windows 10/11, but I cannot get video or screen share feeds to work when using MsRdpEx (audio redirection works fine with SlimCore). I am curious if there is anything you can think of that may prevent the video / screen share logic from working when using MsRdpEx?

:)

[awakecoding]

I don't have an environment to test either the legacy WebRTC or the new Teams SlimCore, but from what I understand, legacy WebRTC works with MsRdpEx + msrdcex.exe, but not the new Teams SlimCore? Does the same copy of the MSRDC launched without MsRdpEx work with it? I'm assuming mstsc.exe doesn't have the required bits for Teams SlimCore.

Off the top of my head, I don't have a clue, so the best would be to capture MsRdpEx tracing logs for a session where you'd expect SlimCore to work but it doesn't. Maybe there's a hint in there about new internal properties, or maybe even new COM interfaces, who knows.

[janscloud]

Hi,

the WebRTC way with audio / video is working sometimes. I am not able to figure out when it will work (better) and when it won't work. I had best luck in one on one ad hoc meetings where video on both sides worked and also screenshare did work. Audio is working all the time perfectly fine.

If it helps and you need a test environment, I can give you access to mine. Will also try to do some logging and provide them.

(I'm not sure about the SlimCore way. I have one Azure Virtual Desktop and some Citrix Virtual Apps & Desktops environments and in none of them the SlimCore AppXPackage made it on my local device yet. But would be nice to have it working with MsRdpEx.)

Best,
Jan

[janscloud]

MsRdpEx-SlimCore.log

SlimCore engine will load and trigger the local "MsTeamsVdi.exe" but Camera does not work. The attached log file should have capture some tries to access local camera.

[GhostlyCrowd]

MsRdpEx-SlimCore.log

SlimCore engine will load and trigger the local "MsTeamsVdi.exe" but Camera does not work. The attached log file should have capture some tries to access local camera.

Same issue I'm experiencing.

Hope for a solution!

[GhostlyCrowd]

Is there any fix in in sight for this?

[Rataplan626]

Or until a solution is there, a way to disable Slimcore in favor of the old WebRTC? Some undocumented registry value maybe? I now have to disable updates and keep Teams to version 24180.205.2980.1757 which is the last one afaik before Slimcore came in. WebRTC works fine for us on our own RDS (2022) environments, both audio and video.

[y4i4vkadc3]

You can disable Slimcore via Cloud Policy
Set-CsTeamsVdiPolicy -VDI2Optimization "Disabled"

We made experience that you have to reset Teams Client to get back to old WebRTC ("avd media optimized") from Slimcore.

This works in our environment with newest Teams Client deployed by Teams bootstrapper.

In rare cases a user gets in slimcore mode even with this cloud policy. Reset of Teams Client helps in this situation.

[Rataplan626]

Thing is we use this on non-azure machines. MsRdpEx can be used to use the new RDP client with your own RDS. And for now we use that in our own environment.

[y4i4vkadc3]

Same here with Windows Server 2022 RDSH.

[Rataplan626]

Ah, great that works indeed. Now this might not be the place to discuss this, but would you know a way to disable VDI2 optimizations for people that just attent a Teams meeting as a guest? Ie. not all users might even be in a tenant.

[awakecoding]

I'm looking at the virtual channel plugins related to this that ship with MSRDC, there are 3:

"VDI Plugin 2.0", MsTeamsPluginAvd.dll, with an "EnableTeamsVdiPluginV2" registry key
"Multimedia Remoter", MsMmrDVCPlugin.dll, with an "EnableMsMmrDVCPlugin" registry key
"WebRTC Redirector", MsRdcWebRTCAddin.dll, with no obvious registry key that I could find

The VDI Plugin 2.0 is clearly the slimcore one which you are trying to use. Do you know if it depends on MMR to work?

[awakecoding]

Ok, so here's what I did so far:

In a Windows 11 VM, I have installed Microsoft Teams and set the registry key to get Teams to try enabling the media optimization:

New-Item -Path "HKLM:\SOFTWARE\Microsoft\Teams" -Force
New-ItemProperty -Path "HKLM:\SOFTWARE\Microsoft\Teams" -Name IsWVDEnvironment -PropertyType DWORD -Value 1 -Force

The good news is that with this registry key, Microsoft Teams tries enabling the media optimization. The bad news is that no matter how many times I restart Teams or reboot the VM, it always tells me I need to restart Teams to enable it.

At this point I haven't been able to see it working with a "happy path" scenario separate from MsRdpEx where it is reported to fail. How have you been testing?

I tried launching msrdc.exe directly without MsRdpEx, but hit an issue where newer versions of MSRDC block all unsigned .RDP files by default, AVD or not. I bypass this check through API hooking in MsRdpEx, but I was trying to see it work without MsRdpEx interference.

Thankfully, I found a new undocumented /SkipAvdSignatureChecks command-line option for msrdc.exe which works around the problem with no API hooking, so I could connect with msrdc.exe, but the Teams media optimization will still not kick in properly.

[janscloud]

Hi Marc-André Moreau (@awakecoding) ,

thanks for your reply!

In my previous tests the MMR was not needed. I'll guess MMR will be needed for Teams useed in browser on AVD. Teams optimization is done with WebRTC Redirector Service. I'm setting up a fresh Windows Server 2025 and give it a shot with and without SlimCore / with MsRdpEx and with "/SkipAvdSignatureChecks" command line. My last tests with working optimization are documented here (in german): https://jans.cloud/2024/08/rdp-teams-optimierung-unter-windows-server-2025/

Best regards,
Jan

[awakecoding]

Thanks for the blog post Jan Mischo (@janscloud)

Ok, so I've tried a few things. If I uninstall Microsoft Teams in the RDP server, then use teamsbootstrapper.exe -p, on first launch, I get this:

When I click Restart Now, I notice that on the RDP client machine, the Microsoft.Teams.SlimCore MSIX package gets installed automatically, so I guess this is done using the RDP virtual channel. The Microsoft.Teams.SlimCore MSIX package, however, doesn't seem to get installed in the RDP server, and I wonder if that's the problem.

The test VM is running Windows 11 24H2 with a local admin user. I'm logged in to Microsoft Teams with an account for a test tenant different from the tenant used for my RDP client machine. I have no idea if Teams somehow expects both sides to have Teams installed and logged in with the exact same user or not.

Anyway, once restarted, I always get this:

I can't click on "Restart Teams to optimize", so all I can do is quit Teams and start it again, only to have the same problem. I have the WebRTC redirector service installed inside the test VM, and it is running.

Are there specific .RDP file options required for SlimCore redirection to be possible in the first place? Maybe I've got a feature disabled that shouldn't be.

Maybe you can confirm is the Microsoft.Teams.SlimCore MSIX package should be installed in the RDP server or not, and if there's a way to force its installation.

[Rataplan626]

I did not know about the /SkipAvdSignatureChecks parameter, that's a real nice one. I can confirm it works on Server 2022 with Teams and the WebRTC 'offloading':

For some reason I can't even get it to install the local Teams VDI (slimcore) component anymore, not even when I use an account from a tennant that doesn't have VDI2Optimization disabled through Powershell, or when I explicitely enable it again. For some reason it defaults to WebRTC now for ALL accounts. Which is for now what I want, but I don't know why it does that.

Also Marc-André Moreau (@awakecoding), you don't need Teams installed locally, I don't have that and until a few hours ago it automatically installed Slimcore locally.