I tried the manual method, watching what the code/player was doing. It looks like Vimeo was sending them in pieces (a new piece every 5-10 seconds). Wether this was to try & prevent copying, for managing live, variable quality/resolution streaming, who knows (anyone?)
I found a decent plugin for Chrome (https://chrome.google.com/webstore/detail/download-vimeo-videos-pre/phpaiffimemgakmakpcehgbophkbllkf) and just gave up on trying to do it myself. The quality seems excellent. This plug-in is free for a day, then a subscription model. I grabbed the rest of the hangouts I didn't have and called it a day.