The video debuted on the LATAM LoL Facebook but is now up in several locations:
"Winter is coming. 冬来たる。@LeagueOfLegends @LoLJPOfficial Winter Summoner's Rift."
For your convenience, here is a youtube mirror of the Winter SR teaser circulating on social media:
The video maintains a clear WIP (work in progress) stamp throughout the video.
UPDATE: Assets included in the 10/31 PBE update but map is not enabled for testing.