У вашего броузера проблема в совместимости с HTML5
Unreal Engine 4.20 has made a few changes to the Sequencer system and we try and highlight a few of the more notable ones.
The Sequencer Curve Editor now supports weighted tangents, the underlying system for storing data uses integers for frame accuracy, and the way we sync the playback has changed. These are just a few of the changes we cover here.