MACROMEDIA FLASH 8-USING FLASH VIDEO ENCODER, Use Manual, Page: 11 / 30

Understanding video standards and terminology 11
An important dependency of the keyframe interval is that it affects the ability of Flash Player
to seek (fast-forward or rewind) through an FLV file. Flash Player can only advance from
keyframe to keyframe, so if you want to skip to different places and pause the frames, you
must use a lower keyframe interval value. If you want to advance to every frame in an FLV
file, use a keyframe interval value of 1. When you reduce the keyframe interval value, you
must raise the data rate for the Flash video to maintain comparable image quality.
Aspect ratios (frame size)
As with the frame rate, the aspect ratio (or frame size) for your document is important for
producing high-quality video. At a specific data rate (connection speed), increasing the frame
size results in decreased video quality. When you select the frame size for your document,
consider the frame rate, the aspect ratio of the source video clip, and your personal preferences
to create a successful video presentation. Standard video display resolutions on the Internet
include 640 x 480, 512 x 384, 320 x 240, and 160 x 120 pixels.
The most common aspect ratio is 4:3 (standard television). Increasingly, 16:9 and 2:1 (wide
screen) aspect ratios are becoming more commonplace as well. Typically, you should encode
the video using the same aspect ratio at which it was originally captured. Altering a video clip’s
aspect ratio may result in a distorted video image. An exception to this practice is when
encoding digital video (DV) formats, whose aspect ratio is slightly different than the 4:3
aspect ratio because DV uses rectangular pixels. When encoding video content captured with
a digital video camera, you must manually specify the frame size of the DV format you are
using to preserve the video’s aspect ratio. For more information see,
“About encoding video
with non-square pixels” on page 12 .
The following list of standard frame sizes can be used as a guideline. You can experiment to
find the best setting for your project.
Frame sizes for 4:3 aspect ratio video:
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Modem (56k): 160 x 120
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DSL: 320 x 240
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Cable: 512 x 384
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Cable/corporate LAN: 640 x 480
Frame sizes for 19:16 aspect ratio video:
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Modem (56k): 192 x 108
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DSL: 384 x 216
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Cable: 448 x 252
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Cable/corporate LAN: 704 x 396
000_FLVEncoder.book Page 11 Friday, August 12, 2005 3:50 PM