ADOBE AFTER EFFECTS 7.0
User Guide
96
HDV Developed jointly by several companies, HDV employs a form of MPEG-2 compression to enable high-
definition video to be encoded on standard miniDV cassette media.
H.264 Also known as MPEG-4 part 10 and AV C (Advanced Video Coding), H.264 can deliver video over a range of
bitrates more efficiently than previous standards. For example, H.264 can deliver the same quality as MPEG-2 at half
the data rate. H.264 is built into the Apple QuickTime 7 multimedia architecture, and will be supported by both of
the rival next-generation DVD formats, HD-DVD and Blu-ray Disc.
Uncompressed HD Refers to high-definition video in an uncompressed format. Without compression to reduce the
video’s data rate, uncompressed video requires relatively fast computer processors, hard disks, and a specialized
capture device.
WM9 HDTV Microsoft’s high-definition delivery format is among numerous formats included in the Windows
Media 9 (WM9) framework. By employing an aggressive compression scheme, WM9 HDTV permits high-
definition video encoding and playback at relatively low data rates.
To change the frame rate of video and film footage
When you import video or film into After Effects, the file’s frame rate does not change. If you output footage to a
different frame rate, After Effects compensates for the difference. The difference between the frame rates determines
how smoothly the layer plays.
Ideally, use source footage that matches the final output frame rate. This way, After Effects renders each frame, and
thefinaloutputdoesnotomitorduplicateframes.If,however,thesourcefootagehasaframerateslightlydifferent
from what you want to output to (for example, 30-fps footage and 29.97-fps final output), you can make the footage
frame rate match the composition frame rate by conforming it.
Conforming the frame rate does not alter the original footage, only the reference that After Effects uses. When
conforming, After Effects changes the internal duration of frames but not the frame content. Afterward, the footage
plays back at a different speed. For example, if you conform the frame rate from 15 fps to 30 fps, the footage plays
back twice as fast. In most cases, conform the frame rate only when the difference between the footage frame rate
and the output frame rate is small.
1 Select the footage file in the Project panel.
2 Choose File > Interpret Footage > Main.
3 Select Conform To Frame Rate, type a new frame rate for Frames Per Second, and then click OK.
Note: Conforming can change the synchronization of visual footage that has an audio track, because changing the frame
rate changes the duration of the video but leaves the audio unchanged. If you want to stretch both audio and video, use
the Time Stretch command. (See “Time-stretching” on page 231.) Keyframes applied to the source footage remain at their
original locations (which retains their synchronization within the composition but not the visual content of the layer).
Be sure to check your files and make any necessary adjustments.
About pixel aspect ratio
Pixel aspect ratio is the ratio of width to height of one pixel in an image. Frame aspect ratio is the ratio of width to
height of the frame dimensions of an image. For example, D1 NTSC has a pixel aspect ratio of 0.9 (or 0.9 width by
1.0 height). It also has a frame aspect ratio of 4:3 (or 4.0 width by 3.0 height).
To Next Page
Loading...