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About data rate
With some video and audio codecs, you can specify
the data rate, also called the bit rate,
which controls the amount of 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 medium
can support while keeping the file size within the capacity of the
target medium. If you plan to stream video to an audience using
dial-up Internet access, this may be as low as 20 Kbps; however,
if you plan to distribute video on DVD, it may be as high as 9.8
Mbps. Data rate guidelines for some media follow:
- DVD production
- The maximum data rate for both video and audio played in DVD-compliant
MPEG-2 format is 9.8 Mbps.
- Blu-ray Disc production
- The maximum data rate for both video and audio played in
Blu-ray Disc format is 48 Mbps.
- 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 for use
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 CD-ROM drive. For example, if you’re preparing a final
video file for a 20x CD-ROM drive (24 Mbps), you might specify around
9 Mbps to account for both the data rate of the CD-ROM drive and
for the system overhead required to move the data.
- Intranet playback
- The data rate can be 1 Mbps 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 Kbps connection is often set to 40 Kbps. The difference accounts
for factors such as data volume and line quality that often prevent
dial-up Internet connections from consistently achieving their stated
data rate. For broadband connections, set the data rate for streaming
video to 128 Kbps.
- Downloading a video file over the web
- The data rate is less important than the size of the video
file on disk, because the main concern is how long it takes to download
the file. However, it still may be desirable to reduce the data
rate 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.
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