See the scale and unsharp filters in ffmpeg:
ffmpeg -i input -filter:v "scale=1280:-1,unsharp=5:5:1.0:5:5:0.0" output
-1 in the scale filter tells
ffmpeg to automatically choose the correct height to preserve aspect ratio. You can change the scaler with the
-sws_flags option, such as
-sws_flags lanczos. For upsampling
lanczos is worth trying. Default is
bicubic. See the full list at
ffmpeg -h full.
My example uses the default
5:5:1.0:5:5:0.0, which I included for demonstration purposes. These values allow you to sharpen or blur chroma and/or luma. See the documentation with
man ffmpeg for more examples.