when I say trim I don’t mean to time trim a file, like getting rid of the last 2 minutes of the mkv file, but to picture trim every frame of the mkv file to get rid of black margins to both left and right of the actual image.

Files were originally recorded on 4:3 aspect ratio (some are movies from the 1950’s) but the encoder somehow created / copied huge black margins to both left and right of the actual image. I want to get rid of these.

Some of my files are 30 minutes long but others 2 hours.

if ffmpeg is the application I need, could anyone knowledgeable enough write the actual command?

can it be done for several files automatically?