MACROMEDIA FLASH MX PROFESSIONAL 2004 - FLASH LITE Technical Information download pdf (Page 17)

by Forest Key and Chris Hock

Encoding Method

The Encoding Method pop-up menu contains three items. Choosing the first

two encoding methods produces a H263 format video stream, which is best

suited for general -purpose video. The third encoding method consists of a

separate video codec that uses a Macromedia proprietary codec optimized

for screen recordings. You can choose from these three encoding methods:

Baseline (1 Pass) uses a consistent bit rate to encode the video stream.

The resulting file size is closely related to the value entered in the Limit

Data Rate To text field, because the data rate will not vary on a frame-

by -frame basis regardless of the complexity and changes in the video

stream.

Better (1 Pass VBR) allows the data rate to fluctuate based on the

content in the video sequence, allocating more bits to areas of greater

complexity. This setting produces better image quality, takes longer to

process, and does not produce easily predictable file sizes (because the

bit rate fluctuates depending on footage).

Screen Recording Codec enables you to record screen operations to a

lossless compression. When you select this option, all other video options

become inactive (are grayed out). Only choose this encoding method

when encoding footage that was created either in screen recording

applications or by compositing graphic elements together in an editing or

effects application. The codec records all pixel changes in the video

stream, which is ideal if there is very little variation in the video (such as

screen recordings of software application demonstrations), but will

produce very large files when used with true video source footage.

Frames Per Second

The Frames Per Second text field enables you to specify the frame rate for

the encoded FLV file. To maintain the temporal quality of the original source

clip, use the same frame rate. For full motion NTSC use 29.97 fps; for PAL

use 25 fps. If you lower the frame rate (which can significantly reduce the

video data that needs to be encoded), the Flash Video Exporter plug-in will

drop frames at a linear rate to achieve the new fps rate. Be sure to choose

an evenly divisible fraction of the original frame rate, or you may introduce

highly distracting “stepping” artifacts.

Table 3: Divisible Frame Rates by Video Standard

FPS Half Third Quarter

"Thirty" 30 15 10 7.5

NTSC 29.97 14.985 9.990 7.493

PAL 25 12.500 8.333 6.250

24p Progressive 24 12 8 6

Film 23.98 11.990 7.993 5.995

Note that 30 and 24 fps are not actually accurate frame rates in common

use. (See the section "Technical Discussion of Video Fundamentals" for

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