Making 1920 x 1080 smaller and keeping the aspect ratio

Just a quick note, when you want to make 1920 x 1080 smaller but keep the same aspect ratio here are the most common sizes:

1080/1920 = 0.5625

For 1920 they're:

1920 x 1080
1440 x 810
  960 x 540 (this is half-size)
  480 x 270
  240 x 135

720/1280 = 0.5625

For 720 they're:

1280 x 720
  960 x 540
  640 x 360 (this is half-size)
  320 x 180
  160 x 90

424/640 = 0.6625

For 640 they're:

640 x 424
480 x 318
320 x 212 (this is half-size)
160 x 106
  80 x 53

If you like math I posted something about how to calculate your own aspect ratio sizes years ago here.