The AOMedia Video Codec 1.0 (a.k.a. AV1) is an open, royalty-free codec optimized for UHD video and intended to compete with MPEG's HEVC.
Quoting the YouTube Developers' channel, "support for AV1 in MP4 within Media Source is available in Chrome 70, and Firefox 63 builds newer than September 13...
🔨 Hive's 3D Viewer has been updated! 🔨 It now supports MDX1100 which should fix a lot of issues when viewing HD models in our 3D Viewer. We encourage you to check it out for yourself and report any issues you find in the Site Discussion board.