You can add '-movflags +faststart' as an output option if your videos are going to be viewed in a browser. This will move some information to the beginning of your file and allow the video to begin playing before it is completely downloaded by the viewer. It is not required if you are going to use a video service such as YouTube. YouTube ​recommends using faststart, so they can begin re-encoding before uploads complete.

$ ffmpeg -i input.mp4 -s 1920x1080 -c:v libx264 -crf 18 -acodec copy output.mp4

$ ffmpeg -i input.mp4 -vf scale=1920x1080 -sws_flags bicublin -tune film output.mp4

$ ffmpeg -i input.avi -vf scale=320:240 output.avi

$ ffmpeg -i input.mp4 -vf scale=320:-1 output.mp4

• Scaler documentation : https://ffmpeg.org/ffmpeg-scaler.html

#
# You can specify which algorithm is used for resizing with the -sws_flags option. For example, to use bilinear instead of the default bicubic scaling:
#
$ ffmpeg -i input.mp4 -vf scale=504:376 -sws_flags bilinear output.mp4
#
# To set multiple flags you can combine them with a + sign. For example:
#
-sws_flags lanczos+full_chroma_inp
#
# You can also specify the options directly in the scale filter, for example:
#
-vf scale=1920x1080:flags=lanczos