decklink filename is hardcoded into Dockerfile

DECKLINK_DRIVER_DEB="./Blackmagic_Desktop_Video_Linux_$DECKLINK_DRIVER_VERSION/deb/x86_64/desktopvideo_12.4.1a15_amd64.deb" &&\

I don't think this is consistent across versions though - you may have to grep the file list for the one matching 'desktopvideo'.