They separated out the video streams and audio streams, so now the only 1080p link you can get is video only (and it uses a different ID to the old 1080p videos, so support needs to be explicitly added for calculating the link).
I ended up writing a wrapper around youtube-dl and ffmpeg to download the MPEG-DASH video and audio streams and mux it because of this. It was a spur-of-the-moment hack, so don't expect error handling.
