Adobe After Effects CS3 Manual de usuario descargar pdf (Pagina 624)

AFTER EFFECTS CS3

User Guide

619

About data rate

With some video and audio codecs, you can specify the data rate,alsocalledthebit rate, which controls the amount

of video information that must be processed each second during playback. Specifying a data rate actually sets the

maximum data rate, because the actual data rate varies depending on the visual content of each frame.

To maximize the quality of encoded video, set the data rate as high as the target delivery medium can support. If you

plan to stream video to an audience using dial-up Internet access, this may be as low as 20 kilobits per second;

however, if you plan to distribute video on DVD, it may be as high as 7 megabits per second. The data rate you specify

depends on the purpose of the video. The following list describes data rate guidelines for some uses:

DVD production The data rate should maximize quality while fitting the entire program within the space available

on the DVD.

Non-DV videotape production The data rate should fall within the capabilities of the computer and hard disk that

perform the final playback to tape.

Hard-disk playback If the final video will be played back from hard disks, determine the typical data transfer rate of

your audience’s hard disks and set the data rate accordingly. If you’re exporting video to be used in another editing

system or to be imported into a compositing application, you’ll want to export at the maximum quality. Use a lossless

codec or the codec supported by your video capture card, and specify the data rate that the editing system supports

for video capture and editing.

CD-ROM playback The data rate for video played from a CD-ROM depends on the speed of the drive. For example,

if you’re preparing a final video file for a quad-speed CD-ROM drive (600 kilobytes per second), you might specify

between 300 and 500 kilobytes per second to account for both the data rate of the drive and for the system overhead

required to move the data.

Intranet playback The data rate can be 1 megabit per second or faster, depending on the speed of the intranet.

Streaming video over the web The data rate should account for real-world performance at the target data rate. For

example, the data rate for streaming video designed for a 56-kilobit-per-second connection is often set to 40 kilobits

per second. The difference accounts for factors such as data volume and line quality that often prevent telephone-

based Internet connections from consistently achieving their stated data rate. For broadband connections, set the

data rate for streaming video to 128 kilobits per second.

Downloading a video file over the web Thedatarateislessimportantthanthesizeofthevideofileondisk,because

themainconcernishowlongittakestodownloadthefile.However,itstillmaybedesirabletoreducethedatarate

for downloaded video because doing so reduces the size of the video file, making it download faster.

In Adobe Premiere Pro, use the File > Get Properties For command to analyze the data rate of files you export.

Specify QuickTime compression settings

1 In the Render Queue panel, click the underlined name of the output module.

2 For Format, choose QuickTime.

3 Click Format Options in the Video Output section.

4 In the Compression Settings dialog box, choose a compressor.

Note: Set the color depth in the Compression Settings dialog box instead of in the Output Module Settings dialog box.

This ensures that non-Adobe plug-ins receive color depth information from After Effects. See step 8.

5 Select a Quality level from Least to Best.

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Adobe After Effects CS3 Manual de usuario Pagina 624

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