From gog support
Cycu93 Aujourd’hui à 12:14
Please remove your current installation of ffdshow and install the latest 32-bit and 64-bit version of ffdshow, reboot/restart your computer and check if the problem still persists. http://ffdshow-tryout.sourceforge.net/download.php
Please also completely remove your current installation of Tex Murphy - Overseer and then install the game again on your computer.
GOG.com Support "