the still photo you just shot. It appears cropped. The video is designed to shoot in 16:9 format that is common to most modern televisions. It ‘masks’ the viewfinder to show you the new framing. This concept is referred to as letter boxing. The masked area in your viewfinder won’t appear in your video, so keep that in mind as you shoot. Frame Rate is almost like a shutter speed. The package that is the video file is essentially comprised of a whole bunch of still images recorded in fractions of seconds in rapid succession. The human brain is able to smooth rapid images into a continuous stream through a concept called ‘persistence of vision’. If you have ever watched an old black and white Charlie Chaplain film, you’ve seen a slow frame rate that makes the footage appear jumpy. Our brains can begin to make a smooth stream at about 8 frames per second (fps), but does a much better job starting around 24 fps. Movies in your local cinema are displayed at 24 fps and appear ‘dreamier’ than faster frame rates seen in modern television. Commonly we see 60 fps as the standard rate for 720p HD and 30 fps on broadcast television in North America and other countries that use the NTSC (National Television System Committee) set of video standards. In Europe, you’ll see 25 fps on broadcast TV, since they use the PAL (Phase Alternating Line) set of standards. More correctly, the frame rates are actually expressed with fractions of frames as 29.97 instead of 30 and 23.98 instead of 24 fps. These fractions arose from the distribution methods of modern television, when engineers were challenged with transmitting color television broadcast signals through the existing power grid. Engineers had to slow down the video frame by a fraction of a percent for compatibility reasons.
Bit Rate refers to how much data describes the video or audio portion of the file. This is measured in units per second as kilobytes (kb), megabytes (mb) or gigabytes (gb). The higher the bit rate, the better the quality of the material. Audio Sample Rate is an additional figure that tells us how often the actual audio is sampled when it is converted into digital information.
Reviewing Quality
With this information in mind, let’s revisit the popular GoPro camera. The 4k setting on the Hero Black+ is tempting to select, however, it is only able to record 15 fps at that size. You can use this for excellent time-lapse footage by speeding it up in the edit suite, but the frame rate is generally too low for smooth video display. That’s why the GoPro retail price is around $500 and a professional 4K Scarlet Dragon camera will set you back $15,000 for the body alone. HD is not all alike. Picking the middle of the road setting at 1080P (more about the P in a future column) on the GoPro is really its sweet spot. You can select from 3 aspect ratios and up to 60fps.
If you want to give your underwater footage that dreamy appearance of a motion picture or produce it on DVD, Blu-Ray or the Internet, then 24 fps is your best selection. If you plan on broadcasting on television, then you should record at 30 (29.97) fps in North America or the PAL standard 25 fps for Europe.
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