Hello. The image quality is pretty good here, however I'm not able to identify the source of this white film. Can you remove a piece of it? It is possible that it's a fungi, though there would have to be a source of moisture for the fungi to survive. Is the wood still relatively wet? This could also be dried resin - if you scrape some off and smell it, does it have a sweet smell, or perhaps like turpentine?
It might be worth calling in a pest control company or perhaps a home inspector so that they could positively identify the material and tell you if there's cause for concern.