tl;dr

''ffmpeg -i input.mp4 -vf scale=320:240,setsar=1:1 output.mp4''

variables

''ffmpeg -i input.jpg -vf scale=iw*2:ih input_double_width.png''

(works on images btw)

fit a rectangle, with padding

''ffmpeg -i input.jpg -vf "scale=320:240:force_original_aspect_ratio=decrease,pad=320:240:(ow-iw)/2:(oh-ih)/2" output_320_padding.png''

text over video, found in ancient text file (might not work)

''ffmpeg -i ordeal.mkv -ss 55 -t 5 -vf drawtext="textfile=slap.txt: fontcolor=white: fontsize=96: x=(w-text_w)/2: y=(h-text_h)/2" out1.mp4; ffmpeg -i out1.mp4 -vf scale=320:180 out2.gif''

strip audio

''ffmpeg -i footage_with_adamvoice.MOV -an footage.mp4''

rotate

''ffmepg -i footage.mp4 -vf "transpose=2,transpose=2" rotated180.mp4''

    0 = 90° counterclockwise and vertical flip (default)
    1 = 90° clockwise
    2 = 90° counterclockwise
    3 = 90° clockwise and vertical flip
   
crop

To crop a 80×60 section, starting from position (200, 100):

''ffmpeg -i in.mp4 -vf "crop=80:60:200:100" -c:a copy out.mp4''

you can use ''in_h'' and ''in_w'', and even things like ''in_h/2-100''