In mstsc.exe, under Local Resources > More.. there is an option for Video capture devices. Which lists my webcam and Devices that I plug in later. I have determined that this option the an RDP file is the string camerastoredirect:s:* So what I have done is ran the following command on my Connection Broker so that this line will be added to rdp file generated by the feed.
Set-RDSessionCollectionConfiguration -CollectionName $CollectionName -CustomRdpProperty "camerastoredirect:s:*"
When I run Get-RDSessionCollectionConfiguration I see the value has been added to CustomRdpProperty along with "use redirection server name:i:1" which seems to be a default on all collections.
What I am trying to solve is, why does my custom RDP property not apply to the RDP files that are downloaded.