Canon Rebel T2i Quick Start Manual page 19

About video image sizes and frame rates:
• 1920 x 1080 is the image size in horizontal by vertical pixels. This is
the size of HD video.
• 24 and 30 are the frame rates: 24 frames or 30 frames per second
(fps).
• In addition to "fps", frame rates can be expressed as "p", to indicate
progressive scanning common to all new cameras. "30p" means "30
fps".
• Choose 1920 x 1080 24 for talking head videos
• Choose 1920 x 1080 30 fps for videos with motion