As is often the case in life, once you break a psychological barrier, it becomes so much easier the next time around to replicate the progress. A few weeks ago, I finally broke into the 1:19's and wanted to try and do it again this weekend.
Armed with a few notes from the data system, I focused on replicating what I did last time and focusing on being more patient in the hairpins (minimizing distance vs. trying to take the "ideal" line). Much to my surprise, the second lap of the day was a 1:19.2! The next session, I got down to 1:18.3, which is the video you're seeing now.
Thanks to your feedback, I positioned the camera on the windshield and placed the mic in the rear engine tray. This seems to be a pretty good setup with minimal wind noise.