DSLR Camera Basics
“Frame size” refers to the horizontal and vertical dimensions of each frame, in pixels. The options available include 1920 × 1080, 1280 × 720, and 640 × 424; the larger the size, the higher the resolution of the movie when viewed on a TV, and the larger the image when displayed on a computer monitor. Note, however, that larger frame sizes produce larger files, reducing the footage that can be recorded to the memory card.
Movies recorded at frame sizes of 1920 × 1080 (Full HD) and 1280 × 720 (HD) have an aspect ratio of 16 : 9, while movies recorded at a frame size of 640 × 424 have an aspect ratio of 3 : 2.