Frame rate – Apple Final Cut Pro 6 User Manual
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Appendix A
Video Formats
385
V
Some video formats use rectangular pixels to reduce the amount of information
stored on tape. For example, DVCPRO HD effectively records 1280 pixels per line (when
using the 720p format), but to save space on tape, the intensity of every 1.33 pixels is
averaged together (a process known as subsampling) and only 960 pixels are recorded.
These pixels are not representing a square area, but a wider, rectangular portion of
each video line. This results in a 4-to-3 reduction in the amount of information
recorded on tape.
Video and image editing programs like Final Cut Pro and Photoshop must compensate
for these rectangular pixels so they appear correctly on a computer display. However,
there are several different pixel aspect ratios in use, and there is unfortunately no single
accepted standard in the industry. The exact aspect ratio used may vary slightly from one
software application to another, as well as among different third-party video interfaces.
These days, the biggest challenge comes when exchanging graphics between
applications that use different pixel aspect ratios, or when using an application that
does not support rectangular pixels with one that does. The key to a simple workflow
is to use applications that can work at the native, non-square pixel image dimensions
and compensate on the computer display. Fortunately, major video and graphics
applications such as Photoshop, After Effects, Final Cut Pro, and DVD Studio Pro can
work with graphics and video at native resolutions. This way, you are always working
with the exact pixel dimensions that you will eventually output to videotape or DVD.
Frame Rate
The frame rate of any motion picture, whether film or video, defines how often pictures
are taken per second. The higher the frame rate, the more accurately you capture
moments in time and reduce flicker during playback. To achieve double the perceived
frame rate (flicker), film projectors actually double or triple the shutter speed, even
though the same frame is repeated two or three times, respectively. This is because
a faster flicker creates more convincing motion. Video uses a similar, although more
complicated, technique called interlacing. For more information about interlacing, see
the next section, “
.” For more details about frame rate, see