Here you go

ffmpeg -i "myVideo.mp4" -vf scale=WIDTH:HEIGHT "new.mp4"

Just replace WIDTH and HEIGHT with your desired size and the input and output file names/paths. On Windows, you can drag and drop the filename onto the terminal with your cursor where you want the path to be, and it will add parentheses for you too. You only need parentheses if the file name has spaces. 🔣

Update from December 1st, 2022

You can choose the scaling algorithm by also adding the option -sws_flags <algorithm>. I think its a really bad name for it.

Example:

ffmpeg -i "myVideo.mp4" -vf scale=1920:1080 -sws_flags neighbor "out.mp4"

<algorithm> can be any of the following values:

• fast_bilinear
• bilinear
• neighbor (keeps pixels)
• bicubic (very common)
• experimental
• area
• bicublin
• gauss
• sinc
• lanczos
• spline