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