MACROMEDIA FLASH MX PROFESSIONAL 2004 - FLASH LITE Informations techniques télécharger pdf (Page 19)

by Forest Key and Chris Hock

medium. For Internet delivery most FLV files are downloaded progressively

to the client computer and then played back from the local hard disk. This

technique provides a wide gamut of bit rates for delivery. For streaming FLV

files, client connection speeds limit the bit rate that you can use.

Table 4 shows the approximate total download times for a one- and five-

minute video clip encoded at 500 kilobits and 2,000 kilobits. Both clips

assume no audio (MOS).

Table 4: Downlaod Times for Video Clips

500 Kbit Video 2,000 Kbit Video

Kbits 1 min 5 min 1 min 5 min

T3 1500 20 sec 2 min 80 sec 7 min

T1 768 39 sec 3 min 3 min 13 min

DSL 512 59 sec 5 min 4 min 20 min

DSL 384 1 min 7 min 5 min 26 min

Dialup 56 9 min 45 min 36 min 179 min

Table 5 lists the approximate data rates that you can use with Flash

Communication Server to reliably stream video to target users on various

connection speeds. These data rates include a 10-percent headroom to allow

for network traffic.

Table 5: Data Rates for Streaming Video

Connection

Connection Rate

(Kbps)

Recommended Maximum

Bit Rate

DSL 1024 800 kbps

DSL 512 450 kbps

DSL 384 350 kbps

DSL 256 225 kbps

Dialup 56.6 40 kbps

Keyframes

The Keyframes pop-up menu enables you to choose between automatic or

custom keyframing. The Keyframe value indicates to the encoder h ow often

to re-evaluate the video image and record a full frame, or keyframe, into the

FLV file. Between keyframes the encoder approximates the full frame by

estimating the full value of all pixels on the screen, principally by comparing

multiple frames an d eliminating information that is redundant.

The Keyframe value can be any number up to 100. When you select Auto,

Flash Video Exporter chooses a keyframe rate that is a multiple of the

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MACROMEDIA FLASH MX PROFESSIONAL 2004 - FLASH LITE Informations techniques Page 19