Comment by cooper12

    ffmpeg -i foo.mp4 -c:v h264_videotoolbox -b:v 1600k foo_out.mp4

On macOS, this uses hardware acceleration to reencode a video at a lower bitrate. My macbook is from 2012, so this does make a notable difference. There's also "hevc_videotoolbox" for H.265 if your machine supports it.