Instead of black letterboxes put blurred video filter from gameplay

Instead of seeing black vertical letterboxes on (Ultrawide) monitors while playing a game that doesnt support wide aspect ratios, enable a filter that would put blurred version of real time gameplay on said letterboxes (in real time, ofc). Something like this exists on social media videos that are filmed vertically and being played back horizontally.
Examples:
stackoverflow.com/questions/30789367/ffm...-video-169-with-blur