In the Export Settings dialog box, the options available in the Video tab depend on the format you’ve specified. Video settings include some or all of the following options:

Codec

Specifies the codec used to encode the video from those available on your system.

Quality

Specifies the encoding quality. Generally, higher values increase rendering time and file size.

Encode Alpha Channel

Enables encoding of an alpha channel into the exported file for formats, such as Adobe Flash Video, that support alpha channels.

TV Standard

Conforms the output to the NTSC or PAL standard.

Frame Width

Scales the output frame’s horizontal aspect to the specified width.

Frame Height

Scales the output frame’s vertical aspect to the specified height.

Frame Rate

The output frame rate for either NTSC or PAL formats.

Field Order

Specifies whether the output file’s frames are interlaced, and if so, whether the upper or lower field is first in the scanning order.

Pixel Aspect Ratio

Specifies the ratio of each pixel’s width to height, which determines the number of pixels required to achieve a given image aspect ratio. Some formats use square pixels, while others use nonsquare pixels.

Bitrate Encoding

Specifies whether the codec achieves a constant or variable bitrate in the exported file:

Constant Bit Rate (CBR)

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 Bit Rate (VBR)

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.

In general, an image is complex and more difficult to compress efficiently if it contains great detail or if it differs significantly from previous frames, as it would in a scene containing motion.

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.)

Target Bitrate

Specifies the number of megabits per second of playback for the encoded file.

Maximum Bitrate

Specifies the maximum number of megabits per second of playback 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.

M frames

Specifies the number of B frames (Bi‑directional frames) between consecutive I frames (Intra‑frames) and P frames (Predicted frames).

N frames

Specifies the number of frames between I frames (Intra‑frames). This value must be a multiple of the M frames value.

Closed GOP Every

Specifies the frequency of each Closed Group of Pictures (Closed GOP), which cannot reference 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

When selected, sets the placement of Group of Pictures (GOP) automatically. (This 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.