Investigate which command-line virtual camera options we have on Desktop Linux.

In a nutshell:

• It must be a command-line tool
• Resolution, output stream, pixel formats, fps should be customizable.
• Ideally, the option should be available on x86_64 and arm
• First of all, it should work on Ubuntu. But the more distributions it covers, the better.
• check licenses

More info is in epic https://bugreports.qt.io/browse/QTBUG-139771

The ticket includes:

• find suitable software
• make sure that it works locally
• create a proof-of-concept script that installs the software (downloading, [opt] configuring+compiling, installing)
• write investigation reports in the task comments.