How to get ffmpeg configuration similar to that of youtube for 480p and 1080p video? I have got a function but the output quality is too low

Question

Hey guys I am learning to develop a website that converts videos to youtube quality (or close enough) 480p and 1080p, I am not much familiar with ffmpeg and struggling with its documentation.

I have these functions,

video_480p      = subprocess.call([FFMPEG_PATH, '-i', input_file, '-codec:v', 'libx264', '-crf', '20', '-preset', 'medium',
                '-b:v', '1000k', '-maxrate', '1000k', '-bufsize', '2000k','-vf', 'scale=-2:480', '-codec:a', 'aac', '-b:a',
                 '128k', '-strict', '-2', file_480p])

similarly I have another function,

new_video       = subprocess.call([FFMPEG_PATH, '-i', input_file, '-codec:v', 'libx264', '-crf', '20', '-preset', 'medium',
                '-b:v', '1000k', '-maxrate', '1000k', '-bufsize', '2000k','-vf', 'scale=-2:1080', '-codec:a', 'aac', '-b:a',
                 '128k', '-strict', '-2', output_file])

Both these functions, transcode the video, but returns low quality videos, Can anyone provide me with the right settings for 480p and 1080p which is similar or close to youtube quality?

Thanks