1. Download ffmpeg
Link to download ffmpeg: https://github.com/BtbN/FFmpeg-Builds/releases
2. Create a *.bat file
Discussion about ffmpeg command line to use: Compress mp4 using FFMPEG · GitHub
3. Create a shortcut on Desktop and drag'n'drop
It will create a new file in same path than the video you want to compress with following name: "original_file_name.extension.compressed.mp4".
You can drag'n'drop several files.