Technical information

by Forest Key and Chris Hock
14
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:
n
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.
n
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).
n
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