I made some fixes for FireWireSDK26 for Monterey (converted from 32-bit to 64-bit, etc.) so I can record from cable box via FireWire. AVCVideoCap produces a .m2t file that plays without problem in QuickTime Player.app. In VLC, you may need to select a different Video and Audio track in the Video and Audio menus depending on the channel that you are recording.
VLC can play the .m2t while it's recording, as long as it's a few seconds behind. If the playback gets too near to real-time then it may stop playing.
AVCBrowser.app has an option to view a video stream in VLC (using a udp
url) but it doesn't work. I don't know if it works with an older version of macOS and VLC which could indicate a problem with my updated code.
I don't know how to update the Interface Builder .nib files for modern Xcode so it would be difficult to update the UI elements.