Using a Vive Tracker with MixCast Capture
MixCast Capture relies on SteamVR's mixed-reality quadrant mode to capture mixed-reality footage. Enabling quadrant mode requires a third Vive tracked device, but unfortunately many titles don't recognize the Vive Track as a valid tracking device. This depends on the version of the SteamVR SDK used in the title.
Thankfully it is possible to convert your Vive Tracker into a controller by updating its firmware. This is a fast and simple process, but as with any firmware update there's some risk of failure resulting in an unusable device, so proceed at your own risk. That said, this method of changing the Vive Tracker firmware was created by an HTC Vive developer. This process is also reversible.
Once the Vive Tracker shows up as a controller in your SteamVR Status panel you're good to go! SteamVR titles supporting quadrant mode should now launch correctly with MixCast Capture!
Instructions from the original post by the creator:
Vive Tracker Role Changer (current version: 0.8)
VIVE Tracker Role Changer v0.8
This tool is for changing the role of the tracker to read in SteamVR as a controller. This is only required for applications that doesn't yet recognize the device correctly, e.g. mixed reality.
Note: While your tracker is reporting itself as a controller, while it shouldn't ask you to update, if it does, do not update the firmware until it's reporting itself as a tracker again.
Hopefully I didn't miss anything with the tool. Let us know how it works. Also, if you guys need this tool for another issue outside of the MR issue that we're aware of, please let us know.
If you don't have a Vive Tracker, you can 'fake' a third controller in SteamVR. Learn how here!