That's not really how video codecs work. Below is a gross oversimplification to bootstrap the parent's knowledge.

Video is usually both temporally compressed (across frames), and over frequency domain (ala jpeg) in the frame itself.

Transcoding is essentially what you're asking for, it downscales the video. It's the cheapest currently or we'd be using something else.

If you just dropped data you'd get that blocky square thing that you get when watching tv or satellite and the signal goes lossy.