Adobe AFTER EFFECTS CS3 PROFESSIONAL User Manual page 615

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.
Specifies the number of megabits per second of playback for the encoded file. (This setting is available only
Bitrate
if you select CBR as the Bitrate Encoding option.)
The following options appear only if you select VBR as the Bitrate Encoding option:
Specifies the number of times the encoder will analyze the clip before encoding. Multiple passes
Encoding 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.)
Specifies the number of megabits per second of playback for the encoded file.
Target Bitrate
Specifies the maximum number of megabits per second of playback you want the encoder to
Maximum Bitrate
allow.
Specifies the minimum number of megabits per second of playback you want the encoder to allow.
Minimum Bitrate
The minimum bitrate differs according to the format. For MPEG-2-DVD, the minimum bitrate must be at least
1.5 Mbps.
Specifies the number of B frames (Bi-directional frames) between consecutive I frames (Intra-frames) and
M frames
P frames (Predicted frames).
Specifies the number of frames between I frames (Intra-frames). This value must be a multiple of the M
N frames
frames value.
Specifies the frequency of each Closed Group of Pictures (Closed GOP), which cannot reference
Closed GOP Every
frames outside of the closed GOP. A GOP consists of a sequence of I, B, and P frames. (This option is available if you
choose MPEG-1 or MPEG-2 as the format.)
Automatic GOP Placement
option is available if you choose MPEG-1 as the format.)
Note: MPEG-1 and MPEG-2 formats include numerous advanced options not listed here. In most cases, selecting a
format or preset designed for your target output sets the appropriate options automatically. For detailed information on
options not listed, consult the specifications for the MPEG-1 (ISO/IEC 11172) and MPEG-2 (ISO/IEC 13818) formats.
Audio options for encoding
In the Export Settings dialog box, the options available in the Audio tab depend on the format you've specified. Some
common audio options include the following:
Specifies the codec used to encode the audio:
Codec
•
AAC (Advanced Audio Coding)
the default for the H.264 format.
•
SurCode for Dolby Digital 5.1
most common encoder for DVD-video. (This codec is available only in Adobe Premiere Pro.)
•
MainConcept MPEG Audio
with Adobe Premiere Pro, After Effects, and Soundbooth.
•
PCM (pulse-code modulation) Audio
other formats.
When selected, sets the placement of Group of Pictures (GOP) automatically. (This
A high-quality encoding format supported by many mobile devices. This codec is
A high-quality encoding format developed for multichannel digital sound and the
A high-quality encoder developed by MainConcept media technologies, and included
A lossless audio format. Files of this format tend to be larger than files of the
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