I have a video file that is a screen recording of some slides. The slides had a 4:3 aspect ratio (1440x1080), but the video file is 16:9 (1920x1080), meaning there are black bars to the left and right. I would like to take a narrow column of pixels from the leftmost edge of the slide (say, the 241st column of pixels) and stretch them to cover the left black bar (and do the same on the right side to cover the right black bar). Is this something that can be done entirely on the command line by ffmpeg?
FFmpeg has a fillborders filter that can be used here.
Assuming a 1440x1080 content area inside a 1920x1080 frame, use
ffmpeg -i in -vf fillborders=left=241:right=241:mode=smear -c:a copy out