Adobe Premiere Pro CS4 - Manual (Page 450)

444 USING ADOBE PREMIERE PRO CS4
Exporting
Last updated 11/6/2011
Render At Maximum Depth Specifies whether Adobe Media Encoder renders sequences containing high bit-depth
assets at their full bit depth.
Bitrate Mode or Bitrate Encoding Specifies whether the codec achieves a constant bitrate (CBR) or variable bitrate
(VBR) in the exported file:
• Constant Compresses each frame in the source video to the fixed limit you specify, producing a file with a fixed
data rate. Therefore, frames containing more complex data are compressed more, while less complex frames are
compressed less.
• Variable Constrained Allows the exported file’s data rate to vary within a range you specify. Because a given
amount of compression degrades the quality of a complex image more than it degrades the quality of a simple image,
VBR encoding compresses complex frames less and compresses simple frames more.
• Variable Unconstrained Allows the exported file’s data rate to vary without limit.
• CBR Constant bitrate
• VBR, 1 Pass Variable bitrate, with the encoder making a single pass through the file from beginning to end. Single-
pass encoding takes less time than dual-pass encoding, but doesn’t achieve the same quality in the output.
• VBR, 2 Pass Variable bitrate, with the encoder making two passes through the file, from beginning to end, and then
from end to beginning. The second pass prolongs the process, but it ensures greater encoding efficiency, and often a
higher quality output.
Note: When comparing CBR and VBR files of the same content and file size, you can make the following generalizations:
A CBR file may play back more reliably over a wider range of systems, because a fixed data rate is less demanding on a
media player and computer processor. However, a VBR file tends to have a higher image quality, because VBR tailors the
amount of compression to the image content.
Bitrate Specifies the number of megabits per second of playback for the encoded file. (This setting is available only if
you select CBR as the Bitrate Encoding option.)
The following options appear only if you select VBR as the Bitrate Encoding option:
Encoding Passes Specifies the number of times the encoder will analyze the clip before encoding. Multiple passes
increase the time it takes to encode the file, but generally result in more efficient compression and higher image quality.
(Adobe After Effects doesn’t support multiple encoding passes.)
Set Bitrate Available only for the QuickTime format. Select to keep the bitrate of the output file constant.
Bitrate [kbps] Available only for the QuickTime format. Select if you want to determine the bitrate. Then, drag the
slider until the hot text displays the desired value.
Maximum Bitrate [Kbps] Specifies the maximum bitrate you want the encoder to allow.
Average Video Bitrate [Kbps] Specifies the average video bitrate you want the encoder to allow.
Target Bitrate [Mbps] Specifies the average video bitrate you want the encoder to allow when encoding video using the
H.264 video codec.
Peak Video Bitrate [Kbps] Specifies the top bitrate you want the encoder to allow.
Minimum Bitrate Specifies the minimum number of megabits per second of playback you want the encoder to allow.
The minimum bitrate differs according to the format. For MPEG-2-DVD, the minimum bitrate must be at least
1.5
Mbps.
Allow Interlaced Processing Select this option if the video content in the sequence is interlaced and you are exporting
to a noninterlaced medium, such as motion picture film or progressive scan video. Deinterlacing can also make it
easier to apply high-quality effects in another program, such as After Effects. If the sequence content does not have
fields, don’t select this option; instead select No Fields from the Fields option.