This seems relevant: https://developer.valvesoftware.com/wiki/Source_Filmmaker https://developer.valvesoftware.com/wiki/Source_Filmmaker In short, Source Filmm

This seems relevant: https://developer.valvesoftware.com/wiki/Source_Filmmaker https://developer.valvesoftware.com/wiki/Source_Filmmaker In short, Source Filmmaker was a never officially released tool that was used as part of the production of the TF2 and L4D promotional videos. It provided tools for recording footage, basic editing, and advanced rendering that went beyond the engine's realtime capabilities.