Scale the input video to a size of 200x100

scale=w=200:h=100

This is equivalent to:

scale=200:100

or:

scale=200x100

Specify a size abbreviation for the output size:

scale=qcif

which can also be written as:

scale=size=qcif

Scale the input to 2x:

scale=w=2*iw:h=2*ih

The above is the same as:

scale=2*in_w:2*in_h

Scale the input to 2x with forced interlaced scaling:

scale=2*iw:2*ih:interl=1

Scale the input to half size:

scale=w=iw/2:h=ih/2

Increase the width, and set the height to the same size:

scale=3/2*iw:ow

Seek Greek harmony:

scale=iw:1/PHI*iw
scale=ih*PHI:ih

Increase the height, and set the width to 3/2 of the height:

scale=w=3/2*oh:h=3/5*ih

Increase the size, making the size a multiple of the chroma subsample values:

scale="trunc(3/2*iw/hsub)*hsub:trunc(3/2*ih/vsub)*vsub"

Increase the width to a maximum of 500 pixels, keeping the same aspect ratio as the input:

scale=w='min(500\, iw*3/2):h=-1'

Make pixels square by combining scale and setsar:

scale='trunc(ih*dar):ih',setsar=1/1

Make pixels square by combining scale and setsar, making sure the resulting resolution is even (required by some codecs):

scale='trunc(ih*dar/2)*2:trunc(ih/2)*2',setsar=1/1