Adobe Premiere Elements 12 - Manual (Page 278)

Compression and data-rate basics
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DVD production
Non-DV videotape production
Hard disk playback
CD-ROM playback
Intranet playback
About compression
About data rate
About compression keyframes
About compression
When exporting a movie, you choose a codec to compress the information for storage and transfer (such as on a DVD), and to decompress the
information so it can be viewed again. The name “codec” comes from an abbreviation of its function of compression and decompression. During
compression, repetitive and unnecessary information in the original file is discarded, causing the original file to lose information. For this reason,
most codecs are considered lossy. Some codecs, though lossy, still allow the file to retain a high level of quality. The DV and MPEG codecs are
especially good at maintaining excellent quality. Compressing video reduces its file size and data transfer rate, facilitating smooth playback and
reducing storage requirements. A variety of codecs are available; no single codec is the best for all situations. For example, the best codec for
compressing cartoon animation is generally not effective for compressing live-action video. When you export from Premiere Elements, you
generally only need to choose your medium of delivery and the application will select the optimal codec for you.
If you intend for your exported movie to be played back from a hard disk or CD, make sure that the codec you use to export your video is
available to the audience for your movie. Most codecs for digital video and the web are already available on a majority of systems. However, if you
are using a codec that’s native to a particular product, make sure that your target audience uses the same product, or can easily obtain the codec
that you used.
If you intend to create a DVD or record to tape, codec compatibility is irrelevant. Your audience only needs to have the hardware necessary to play
back the file.
About data rate
With some video codecs, you can specify the data rate, which controls the amount of video information that is processed each second during
playback. Specifying a data rate in Premiere Elements sets the maximum data rate because the actual data rate varies according to the visual
content of each frame.
The data rate you specify depends on the purpose of the video. The following list describes data rate guidelines for some uses:
The data rate should maximize quality while fitting the entire program within the space available on the DVD. By default,
Premiere Elements automatically adjusts the DVD data rate.
The data rate should be well within the data transfer rate of your hard disk because the video will be played back
from the hard disk to the recording device. Check your documentation for information on the data transfer rate of your hard disk.
Determine the typical data transfer rate of your audience’s hard disks and set the data rate accordingly. Generally, 7200 rpm
hard disks have sustained data rates of 20 to 35 MB per second, which is high. In comparison, the average data rate of digital video is 3.6 MB per
second. So, to achieve high-quality playback, you may not need to set the data rate as high as 20 to 35 MB per second. However, if you are
exporting video for use in another editing system or in a compositing application, such as Adobe After Effects, export at the maximum quality. Use
a lossless codec, which is one that compresses without discarding information, and specify the data rate that the editing system supports for video
capture and editing.
The data rate depends on the speed of the CD drive. For example, if you are preparing a final video file for a double-speed
CD-ROM drive (300 kilobytes per second) you might specify between 150 kilobytes and 200 kilobytes per second to account for both the data rate
of the drive and the system overhead required to move the data.
The data rate can be 100 kilobytes per second or faster, depending on the speed of your intranet. An intranet is an in-house
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