Adobe After Effects CS4 - Manual (Page 725)

719 USING AFTER EFFECTS CS4
Rendering and exporting
Last updated 12/21/2009
To play an animated GIF file, the web browser first loads the entire file into memory and then plays it from memory
(not from disk). To prevent excessive delays before playback begins, and to avoid using too much memory, an
animated GIF should have a short duration and a low frame rate. Frame rates of 5 frames per second (or less) are
recommended, unless the duration is very short (1 second or so).
When you render a movie to the animated GIF format, colors are dithered to an 8-bit palette (256 colors). Before
rendering your final movie, render a test composition so that you can adjust colors if the results are not what you
expect. You can create a color palette in Adobe Photoshop if the default Web Safe or System color palettes don’t give
the results that you want.
A pixel in an animated GIF file is either completely opaque or completely transparent. When rendering an animated
GIF movie, After Effects must convert the finely graded alpha channel of the composition to this much simpler kind
of transparency. The transition between transparent and opaque areas is abrupt, and may not be desired for more
subtle visual elements.
You render and export a movie as an animated GIF file using the render queue. Animated GIF is one of the formats
available in the Format menu in the Output Module Settings dialog box.
For additional information about the limitations of the animated GIF format and instructions for creating animated
GIF movies with After Effects, see the
Adobe Technical Support website .
Photoshop Extended offers more control for creating animated GIF movies. Create your animation in After Effects,
render and export to an intermediate format (such as a QuickTime movie), open the movie in Photoshop Extended,
and export to animated GIF using Save For Web & Devices.
More Help topics
“ Basics of rendering and exporting ” on page 688
Audio export settings
In the Export Settings dialog box, the options available in the Audio tab depend on the format you’ve specified. One
or more of these options appear on the Audio tab:
Audio Codec or Codec Specifies the codec used to encode the audio data. These options are some of the most
commonly used codecs available through Adobe Media Encoder:
• AAC (Advanced Audio Coding) A high-quality encoding format supported by many mobile devices. This codec is
the default for the H.264 format.
• AAC+ Version 1 Uses spectral band replication (SBR) to enhance the compression efficiency in the frequency
domain.
SBR is a technology that enhances audio codecs, especially at low bit rates and is based on harmonic redundancy in the
frequency domain. The audio codec itself transmits the lower and mid-frequencies of the spectrum, while SBR
replicates higher frequency content by transposing up harmonics from the lower and mid-frequencies at the decoder.
• AAC+ Version 2 This version of the AAC codec couples SBR with Parametric Stereo (PS) to enhance the
compression efficiency of stereo signals.
The AAC+ Version 2 bit stream is created by down-mixing the stereo audio signal to mono along with Parametric
Stereo information used to describe the spatial intensity stereo generation and ambience regeneration at the decoder.
By having the Parametric Stereo information coupled with the mono audio stream, the decoder can regenerate a
faithful spatial approximation of the original stereo panorama using very low bitrates.
• MainConcept MPEG Audio A high-quality encoding format developed by MainConcept, and included with Adobe
Premiere Pro, After Effects, and Soundbooth.